adamk24
11-23-2004, 11:57 AM
Welcome to my attempt to make a rather complete guide to turbo chargers. I was going to try and explain some basics about turbo charging and how to select the proper turbo in another topic about honda engines, but I got part way into it and it became obvious I was going to need alot more space to properly teach what I wanted to. So I figured I'd just start a new topic on the subject. I wont be able to write it all in one sitting, however I will try and make updates often to try and get it near completetion as quickly as possible.
If you are new to turbos I suggest you read on, or even if you think you know everything there is to know about them, I bet you'll be supprised with how complex finding the perfect matching turbo can be. However, sence there is so much to be said, I shall divide my prolonged rant into sections. I'll start off with the basics and go from there. I'll try and make large headers to let you know what section your in, to help vet's skip to the good stuff. Well if your ready to begin your turborific future, lets get going!
TURBO BASICS
If you think a turbocharger is something that fills your cell phone battery really fast, than this section is for you. First we are going to talk about the basic operation and function of a turbo, as well as some basic descriptions of how they are made up and why they are made the way they are. As always I am going to try and focus as much as possible on the most recent technology, rather than the most common or most avialable, simply because as time goes on this information will help you the most. Also, alot of people know what worked 10, 15 or 20 years ago, but very few stay up to date with the latest and greatest, so I find it best to stay current.
The first thing to know about turbochargers is this. They make power. :roll: Despite their many advantages, the most obvious one is that on any engine, in any condition they will increase your power. Basically what a turbo functions as is an Air Pump. In much the same way a water pump allows water to be taken from the water table 45 feet down, up to your sink, an air pump supplies more air than your engine could normally take in. Basically any naturally aspirated (N/A will be used as an abriviation. N/A means that the engine is not force inducted, and relies on engine vacuum created by the downward movement of the piston to pull in air) engine can only take in as much air as is allowed by how much vacuum force it can create. This is the main reason why bigger displacement engines make more power, because their swept area allows them to pull in more air for combustion. An air pump, such as a turbo compressor or a supercharger pushes air into the cylinder rather than making the engine have to pull it in. This alone makes power (example: try jogging for a while, then try jogging with an air mask on. The supply of air effortlessly flowwing into your lounges make it alot easier to keep jogging) however, as far as thermodynamics are conserned, it only retrieves the power that is otherwise lost by the engine having to work to pull in air. How a turbo really makes power is by compressing the air that enters the cylinder.
Compressed intake air is refered to as 'boost'. It is ushally rated in either BAR (a reading of a numerical value starting a 0 for atmospheric and increasing upwards. At 1 Bar the pressure is 14.7 psi, or 2 times atmosphereic pressure. Basically 1 Bar is one atmosphere of pressure.) or PSI (pounds per square inch). What this means is that the density of the air going into the engine is increased to add more power. What that means, is that the molecules of intake air are pressed closer together, so that for the same volume of air going into the engine, more air is contained in the cylinder, giving more oxygen for combustion. Add more fuel to burn with the extra air, and you get more power.
Now, that was rather basic information, only my lack of useable vocabulary probably made it sound like rocket science. But assuming that you now understand why a turbo makes power, its time to explain how a turbo goes about making it. You see there are not very many methods of which to add power to an engine. Sure there are alot of things you can do to make it more powerfull, but really you are only doing one of three things. The first is making it easier for the engine to operate, thereby freeing up previously lost horsepower. This would include fuel system modifications (that dont include adding more fuel to combustion), ignition system add ons, head work and cams, any form of porting, intake/exhaust mods or anything that makes power on a N/A engine. The next is forced induction which includes turbo chargers, superchargers, electric air pumps, adding more fuel via fuel modifications, or vacuum pumps (otherwise known as exaust pumps, they have not been in production for over 70 years, but their function is basically to create a vacuum force in the exhaust system to help pull the intake air in rather than push it). The third method is chemical forced induction, such as nitrous oxide, which changes the intake substance from air to... something other than air (a something ushally containing more oxygen, because it wouldnt really make sence to force your engine to take like hydrogen or something..... unless you like broken stuff....)
Ok, so that was a bit off topic, but basically what im getting at is that there are not many ways to increase the power of an engine, because this is not a perfect world and the law of conservation of energy states that energy has to come from somewhere, and often things cost more energy to run than they make it. So just how does a turbocharger make power?
A turbocharger is basically an exhaust driven air pump, meaning it has one large housing with a turbine wheel inside (like you would find in a hydro-electric generator or those big wind power thingies.... ) that is being pushed on by the exhaust gasses, and another large housing with a compressor wheel, which is a shaped circular blade that uses the clearance between it and the housing to catch, move and compress the air going into the engine. The two wheels are connected via a shaft that makes them spin at the same speed. The exhaust turbine drives the air compressor forcing air into the engine. This is the means by which a turbo gets its power, and why they are so kick ass (highly technical term). Because they reuse the heat energy lost in the exhaust system, they are recovering already lost energy to make power, unlike other systems like superchargers that use engine power to make power. Here is a good picture showing the two housings.
http://img.photobucket.com/albums/v517/Adamk2424/turbo-parts.gif
Hopefully now you understand how a turbocharger works, as far as the basics. But before we head to the next section just a few more things to know about turbos and how they work. First off the center section of the turbo. This section contains the shaft, bearings, oil and coolant passages, carbon, coolant, air and oil seals, and often the housing hold down assemblies.
The shaft is a hard metal rod that connects the two wheels together and transmitts power from the exaust to the intake wheel. It spins on a set of bearings, which we will talk more about later. Not all turbos are water cooled, but most modern turbos use coolant as a method of controlling heat transfer from the exaust side to the intake side (in other words minimizing it) as well as prolonging the life of your bearings and housings. The oil passages provide lubrication for the shaft and bearings as well as helping to keep them cool. The carbon seals are metallic scrappers that help prevent carbon build up in the exhaust housing as well as carbon from entering the center housing and clogging in the oil. Coolant and oil seals are pretty self explainitory, and air seals keep the air in the compressor housing and not in the coolant or oil passages where it doesnt belong.
Other basic things about turbo charger systems are Intercoolers and Compressor Bypass valves or Blow of valves (BOV for short). Intercoolers go by many names, here are some of the most common: Aftercooler, Intake Air Coolers, Charge Air Coolers, FMIC (front mount intercooler), Intake Charge Heat Exchangers, or big shiney thing at the front of your car to get the girls to notice you... Blow off valves can be used for the same purpose (getting the girls that is) as they can be modified to be very loud. The basic Function of a BOV is to redirect air back into the intake side of the compressor before it reaches the thottle body, to prevent compressor surge on throttle lift. (more on this later) Intercoolers do exactly what they sound like they do. They cool the air going into the engine, because as we all know, cooler intake air = :mrgreen: . Here is a nifty picture showing basic construction of an intercooler.
http://img.photobucket.com/albums/v517/Adamk2424/hmt60203e.jpg
http://img.photobucket.com/albums/v517/Adamk2424/hmt60203g.jpg
Basiscally the air goes into one side, is directed through anyone of a number of tubes inside the intercooler, which are incontact with cooling fins. The hot air goes in, is cooled by the cold aluminium and comes out cooler. The aluminium gets hot, which is cooled by the outside air flowing over the cooling fins. Later I will talk more about other types of intercoolers, including air to water and water injection, but for now here is a picture showing the layout of your basic turbo system.
http://img.photobucket.com/albums/v517/Adamk2424/turbo-plumbing.gif
Now that the basics are out of the way, its time to get to it! Im not sure what order I should go in, but I think I will try to save the most complicated stuff for later on. So pick a subject and read on!
MAKING POWER WITH A TURBO VEHICLE
If your reading this, Im sure your not interested in turbos because of their awsome fuel economy, so lets get right to the good stuff. How to properly make power with a turbocharged engine. Although it is easiest to start with a stock engine made for boost, I will cover how to build and prep an engine for turbocharging.
First off, if your car comes stock turbocharged, you are on easy street. More power is just a trip to the hardware store away. However, the biggest problem with having instantly adjustable power is that people dont know when to call it quits, and over boost their engines. Doing proper research into what works or doesnt work for your application is a must! Always know what your doing, and the limits of every part on your car. This cannot be over emphized. Know what the limiting factor in your system is and leave a 15% barrier at all times. Respecting this limit will keep your parts working properly, because boost is no fun when its broken.
A good example is a 2nd generation DSM (eclipse, lazer, talon) with the turbo 4G63 engine. Rated at 210 hp stock with a tiny t-25 turbo, there is only a fair amount of room for increased power before you will need to upgrade turbos. However, that doesn't mean run out and get a new turbo right away. Know the limits of the parts on the car, and start with the weakest link. No point in turning up the boost when the stock BOV leaks, limiting your boost to 12 psi, when its already set at 14.7 from the factory.... simply replacing this unit on 2nd gen. DSM's adds an effective 3 psi and about 15 whp.
So once you determine what your goals are, and what stock parts on your car will work, its time to look at upgrades. Here is a list of some of the most basic things any turbo owner should get.
The first is a full new exhaust system. Turbos get their energy from the exhaust coming out of the head. However, the gasses have to go somewhere when they leave the turbo, and its hard to push gass out if it has no where to go. Freeing up back pressure is the easiest and most reliable way to make power in a turbocharged vehicle. A first generation DSM can make over 65 hp with simple exhaust work, on a stock car! For bang per buck, its hard to beat a good 3" or larger exaust system. Heres what parts you need to look for.
1) O2 sensor housing. This unit mounts to the back of the Exhaust housing of the turbo. Not all cars will have this separted unit, as some will have a one piece downpipe that connects the turbo to the cat. However, if your vehicle does have this unit its most likely horribly restrictive (unless its an Lancer Evolution, whos o2 housings are beautifully designed), and should be the first unit to be replaced.
2) Downpipe. The most important unit to replace, is the downpipe, as it is the first piece of tubing in the system. What makes it so special is all of the important things that take place before the exhaust goes through the cat. First the wastegate gasses, which will be either divorced or integrated (which I will cover later) must rejoin the exhaust before the cat. The basic rule on internal wastegates is the smoother the transition back into the exhaust the better. Waiting to rejoin the tubing after the first bend is ideal, but most units simply dump it into a wall at the face of the downpipe. This is horribly restrictive as well as possibly damaging to the turbo if you run into a lean condition. Allowing the wastegate gasses their own passage is what you really want, however a simple wall a few inches long separating it from standard exhaust gas flow is ok. Then allowing it to smoothly flow into one pipe helps keep back pressure down. Another important feature of the downpipe is that it must bend alot to reach from the turbo outlet to the cat. This means that its design and smoothness will have a major impact on the efficiency of the exhaust system. Elliminating kinks and bends in the stock system is where your power will be made here.
3) Cat back. From the catalitic converter back is called the cat back portion of the exhaust system and seeing as its the longest part, it is very important. Resonators are good for keeping the engine quiet, but kill power. My rule is, turbos work as effective exhaust mufflers already, killing loud pulses from the exhaust valves. So Straight pipes into smooth mufflers is my favorite, keeping back pressure to a minimum. Although your choice of exhaust systems make a huge difference in the sound of your N/A vehicle, turbo cars are less likely to totaly change sound from one system to another, so Its hard to recommend any one brand, but Im a fan of Greddy turbo exhaust systems, just because they do a good job at alot of systems for alot of cars without hugely expensive prices.
4) Catalytic Converter. Now, at least in america, it is required that you do not make any modifications to the factory catalytic converter if you want to drive on the streets. However, no will will ever notice if you put an after market high flow cat on. But even that is to much trouble for most people, so damn the environment, I recommend just running a straight pipe in place of the factory cat on turbo cars. You make so much power by taking the cat out, its hard for me to justify spending all that money for a high flow cat. You can always swap the cat back on for emissions anyway.
I will get into more factors that make power in the exhaust system when talking about making custom turbo systems in the next section. The next area to look at improving on your turbo car is the intake tract. Basically using the same principles as a n/a intake system, the larger the piping the better, the shorter the piping the better, and the cooler the intake air the better. Also dont forget a filter. Some people will tell you that you dont have to run a filter on a turbo vehicle. This is monumentally stupid. The same dirt that goes into the turbo is going into the engine. The only thing that could possible happen diffferntly is the dirt clogging in the turbo rather than in the oil in the engine, which isnt any better really. Ok, well yes turbo cars can get away with a little more particulate matter in the air, because their higher combustion temperatures will burn some of the heavier stuff that might get sucked in, however it is not enough of a factor to risk your engine or your turbo. If you want, just buy a $5 foam filter off ebay that come pre-made to mount to the compressor inlet of the turbo. It flows great and filters.... well... not so great, but it will keep everything large enough of concern out. A friend of mine once ran his car with no filter and got a stick thrown up from the road lodged in his turbo, which basically shattered the compressor wheel, so dont risk it.
My favorite intake method on a turbo car is just a 2 or 3 inch long aluminium pipe with a filter on the end that reaches away from the hot exhaust area to a cooler part of the engine bay. It doesnt need to be completely sealed off, just in a cooler part will help out. If your car has an air metering system such a DSM, Skyline or 300zx, you will need to build your intake system around this unit, unless you plan on going after market engine management, but I would see no reason to do that. These systems work great in my opinion. As compared to stock N/A cars, that freak out when they see boost, or have no idea what to do once you start changing the stock airflow charicteristics, these systems actually go, "alright he's flowing 234 cfm of air, looks like its about 68 degrees outside, lets give him an extra 2 degrees of pulse width on that injector pulse." Its a very good system for quickly adjusting boost levels.
Another thing about the intake tract on a turbo vehicle, is the intercooler. Intercoolers are a gift from heaven when it comes to running boost. Back in the less than impressive technology of the 1970s and early 1980s, more and more cars were coming turbo charged from the factory. The problem was that the huge heat that they generated for a number of factors (one is that they used horribly in effecient turbos that made more heat than they did power, another is that they did not water cool their turbos, another yet is they did not yet understand that the flow charicteristics of the exhaust housing greatly determines the overall performance of a turbo on an engine, and using... well I have not gotten to this stuff yet, but its very complicated so I will get to it later), ment that they were only lasting around 60-70,000 miles before they would die. Now back then this wasnt to good, but it wasnt that bad either. Today this would be 100% unacceptable from a new car. So, they started thinking of ways to try and cut down on the intake temperatures.
Now dont get me wrong, Intercoolers are nothing new. The have been around for almost as long as the turbocharger, however its one of those things that makes you wonder, "why didnt they do that earlier...." like finding out that the lead in gas is collecting in the ground water, putting something to reduce the intake temp. on a turbo car falls under the catagory of 'duh'. Today you wont find a factory turbo car with no intercooler (at least I dont think you will, I just know someone will generate a picture from somewhere), but because of the improvements in turbocharger design and construction, it is again possible to make a low boost turbo system with no intercooler. Now I'm not going to recommend anyone do this, but their are benifits having no intercooler, such as increased throttle responce, higher compressor efficientcy (because there is no pressure drop like you would get in an intercooled system) reduced cost and complexity, and smaller overall packaging making it easier to fit in tight places. However, even a small intercooler does wonders for keeping down intake temps, as long as it has proper air flow.
There are basically two types of intercoolers. Air to Air and Air to Liquid. Air to Air intercoolers work like the basic intercooler I described in 'turbo basics'. They send air from the turbo through in the inside, while air from outside blows across the fins like a radiator, and cools the intake air down. This then goes into the throttle body cooler and happier. Now there are a few different types of air to air systems but they all basically work the same. Some intercoolers are fin rack style (most stock units are of this design), and most aftermarket units are bar and plate style. (Basically alternating possitioning of the plates to create passages on the inside for the air to travel in, then filling in the gaps with fins for cooling.) I prefer bar and plate, because of its smoother flow and lower pressure drop, however as far as actually cooling the air, the stock units will work better (dont argue it, its true). Air to Liquid or Air to Water intercoolers work by the air going through an intercooler that is surrounded with cooling water rather than air. Air to Liquid intercoolers however have alot of advantages compared to air to air, such as the ability to cool the air much faster, and to lower the air to temps below that of room temp. by running ice water or other cold liquids in the system. Also because you only need to keep the water cool by running a heat exchanger for the water in the system (similar to an external oil cooler) you can place the unit much closer to the throttle body, meaning less piping which means less air to compress to get on boost, which means faster spool up.
However, there are some major disadvatages to water cooling systems, such as complexity and cost. They are very expensive and extremely hard to properly route. As you will need a tank for the water, a fill area with a pressure holding cap, water lines, a heat exchanger, a pump to flow the water through the system, the cooler its self and a method of removing air from the system (often a sprayer nozzle). The other major downfall to this system is that, where an aluminium FMIC will never heat up to much as long as it has good airflow, a water system has a harder time keeping its self cool during prolonged driving. For drag racing this is not a problem and I highly recommend water intercoolers for their ability to make more power, colder air and to cause less pressure drop, but for daily driving or for track racing, an air to air unit is preferable.
Another important piece of the intake for a turbo system is the compressor bypass valve, or BOV. When it comes to stock units, the first generation DSM unit is about as good as it gets, setting the standard by which all valves are measured against even to this day. Skylines, Rx-7's, Evos and S-15 silvias all use units almost directly copied from the first gen. eclipse/talon/lazer. Strangely then, why Mitsubishi decided to replace this outstanding unit with a crappy piece of plastic crap on the second generation DSM, I have no idea. But basically, there are only 3 types of BOVs that you will see out there. The first type, such as the 1g dsm, is called a lift valve, which basically means it uses spring pressure on both sides, and uses vacuum pressure to open the valve. This is identical in its operation to the other most common type of valve, the poppet valve. Basically they both use a spring with a vacuum port at the top of the spring chamber, so that on throttle lift, the negative pressure (vacuum) that is caused by the throttle plate going shut, over comes spring pressure and opens the valve, which basically just opens a loop back to the start of the intake system. Where the lift valve is different is that their is a second spring on the bottom of the valve to help push it back up faster when you get back on the gas, as well as helping to hold the valve closed tighter when under boost. This is the main problem with poppet valves. They tend to leak under high boost conditions because they have no secondary support springs to help hold the valve shut. This is no problem on well built aluminium aftermarket units with heavy duty springs and well sealed pistons in the BOV cylinder, but on stock plastic units with wimpy springs, leaks are quiet frequent.
The only other style of valve that I am aware of, is the Sequential unit. Basically this is a Lift valve with a timed push rod in the center that actuates a secondary port in the air out side of the housing. In english, that means that when you let off the gas and the BOV activates, it starts with the spring letting just enough air out to keep the turbo from surging, but the main body of the valve is still closed, holding in as much boost pressure as possible. After about .5-2 seconds after vacuum was first detected, if the valve is still in vacuum the secondary spring actuates and opens the main piston. This is used to keep boost pressure from dropping during shifts. They work very well, however many of the valves in the market that claim to be 'sequential' are acutally just lift valves, such as the HKS SSQ BOV, which besides being a very long list of Letters, is just a standard poppet valve that lays sideways and sounds cool.
Before I continue, it has been pointed out that I need to explain the difference between a dump valve and a bypass valve, so here goes. Basically, a BOV (Blow Off Valve) will allow the compressed intake air to vent into the engine bay whereas a CBV (Compressor Bypass Valve) will return the air into the intake side of the compressor. As far as a performance stand point, there is very little reason to use a BOV over a CBV. A bypass style valve makes the turbo work alot less hard on re-spool because the air going in is already partially compressed, as well as being pre-cooled by the intercooler (ok not as cool as ambient air, but because its already compressed it will be cooler coming out the other side than ambient air). Also, on many systems that use a CBV in factory form coupled with a mass airflow meter, like a DSM or Skyline etc... the stock ecu will predict that the air being vented from the valve will be re-entering the intake system rather than being vented to atmosphere. Placing a BOV on this type of system will cause your car to run temporarily lean on throttle lift, so using an AFC (air fuel controller) to adjust this may be nessisary.
As for BOV's advantages, the only one I can think of is the sound. Where as a CBV is very quiet, and difficult to hear unless your really listening for it, a BOV makes alot of racket. This is the primary reason why people use BOV's over CBV's. One more thing to mention, is that on vent to atmosphere valves, make sure that A) the horn of the valve is not facing to the sky, which could cause water to be pooled in the opening and get inside the valve body, causing wear and failure, and B) If it is rather dusty in your area using a filter on the end of your BOV is a good idea, as it sucks a little air back into the intake before it has time to close.
Ok, after intake and exhaust on a turbo vehicle, the next thing you should look at is your fuel system. Obvioulsy, the fuel system is very important to any engine setup, but on a turbo vehicle things become alot more complicated. To start I will talk a little about how a stock turbo fuel system works, before moving on to aftermarket systems, upgrades and parts, and finally some advice about the fuel system and tunning.
Ok, so most stock fuel systems on turbo vehicles operate on this philosophy, 'turbo cars need a big safety margin.' That means that they need to run rich most of the time, to prevent from ever going lean. And just for the record, lean engine conditions + boost = expensive broken parts. This means that there is some power to be made by tweaking the system and leaning it out in places where its a little to rich for its own good. Im not going to get into that just yet, but some cars such as the Evo8 can make over 30 hp with no other mods, just from a good ecu tune. (for more info check out Vishnu performance at http://www.vishnutuning.com/ , normally I wouldnt plug a company, but they are one of my favorites).
The reason why I wont be talking about ECU tunning just yet is this section is about stock ecus, and no one is going to thin out a stock ecu on a turbo car, when they can just turn up the boost rahter than reducing the fuel. This obviuosly achieves the same result while making more power. Now, the ecu will of coarse compensate for the extra boost with more fuel, but as you start to push the limits of your stock fuel system, you will need to start upgrading parts. But anwyay, back to stock. Most turbo cars are going to use a honeycomb style mass air flow meter to read how much air is entering the engine (some use an air flow sensor before the throttle body to read boost as well, on top of air flow) and adjust fuel accordingly. This is good for us because this means we can pump the boost without having to tell the engine to add more fuel. Now, if you were paying attention, I said MOST turbo cars use this system. By that I ment that most modern cars have gone to less tunning friendly systems. A good example is the Dodge SRT-4. The car its self is possibly the best performance buy of all time, however because of its wierd exhaust manifold design (which uses the manifold and turbo exhaust housing as a single casting with an exhaust arm aka o2 sensor housing that is shaped so wierdly that almost no after market companies can make units that work better and dont leak) and crazy engine management system, the car is a tunning nightmare. Now dodge does offer factory perfomance stuff, but if I bought one, the first thing I would do is put in a completely new aftermarket computer. Heres why.
The SRT-4's method of controlling how much boost the engine is running is based on the known flow charicteristics of a stock SRT-4 engine. This means that if the engine reads the temp at 75 degrees and the rpm at 5100 and the turbo at full spool, it will open the wastegate (example only not actuall figures) 83% to keep it at the correct amount of boost, and inject 219 cc's of fuel for combustion. This is all well and good, untill you start wanting more power. Ok, so say you put an aftermarket exaust on it. "its just piping" you think, it shouldn't affect anything much with the engine. Normally you'd be right, but unfortunately because changing the backpressure by 3 psi completely changes the air flow charicteristics of the engine, and now when you give it 60% throttle the turbo spools up alot easier because it has to work less hard to push the exhaust gas. So now you have to much boost and a computer that is lost as to what is going on, making your engine run lean and knock. The Ecu see's the knock and puts you into dumbass mode, otherwise known as limp home or low power mode.
Now some people will ask "Why do they do it this way? If it only causes problems, why dont they stick with the what worked in the past?" Well the anwser is two fold. First, it doenst only cause problems. This method of engine management works better at reducing emissions, increasing fuel economy, and preventing damage to the engine. Also, the car industry does not want people to modify the cars they sell (at least, some of them dont.) When people start turning up the boost and making more power, things break, and because people lie, alot of parts get covered under warrentee, and the company loses money. By making it more difficult to tune, they save costs down the road. But dodge found an even better way to do it. They made a car that they knew everyone would want to tune, and gave it an impossibly difficult engine management system to crack. Then they offer us THEIR parts to make power. Its a brilliant idea, even if I think the parts they offer suck.
But personally I dont care If my exhaust is killing pengiuns and chipmonks, I want more boost. So if your looking at seriosly modifiying your car, either stick with the stuff a few years old, or look for aftermarket ecus. (the exception to this rule is subaru/mitsubishi, they seem to WANT us to blow up our cars, and still sell the good stuff).
Ok, aftermarket management. I wont be getting into this too deep, as it will be covered in great detail in the custom turbo car section later. But for now, just some basics about what to look for.
The most important thing to think about when looking at aftermarket controll units, is there tuneability. What do they let you change, and what options do they offer. Do they have dual stage boost controll settings? Do they offer multiple selectable fuel maps? And what are you going to have to do to get those maps? Does this company offer pre-tuned maps for download on line? Or will you have to take your car to a shop to get tunned? Things like this will be your biggest consern when picking an engine management. All systems should do their job of suppling enough fuel at the right time to prevent bad things happening, while still keeping your bumper from catching on fire and making you go through a gallon a mile of fuel. Other than that, its the options they offer that really make the difference. So let me explain what some of those options are.
First off, it is always a good idea to find an ecu that has pre-made maps avialable for your application. As I stated before, I like Vishnu tunning for evo's and wrx's, because they offer a huge range of pre-made maps for download on their web site, and I've seen alot of heavy hitters running their systems. Having to take your car down to a shop to get tunned not only takes alot of time, but is very costly as well. And speaking from experience, the extra expense is not worth the slight performance pay off. Dont get me wrong, a custom tune will almost always be better, but if your asking if its worth it, Id almost always say no, if pre-made maps are avialable.
Another feature to look for is dual stage boost settings. Although this option used to only be offered on the more expensive ECU systems, it has been becoming more and more common and when I checked just prior to this article, it seems that most of the companies out there today offer it as an option. However if you asked me of its usefullness, Id tell you not to bother unless you were having traction controll issues. Basically what a dual stage system does, is limits your boost in a certain gear to keep you from just spinning the wheels. This means you could set up your car to run 16 psi in first, 21 in second and max boost in all the following gears to help you get down the track faster. My problem with this is it doesnt offer me the flexibility I would want in track or street driving. For the drag strip, this can be an invaluable tool, but for my purposes, I prefer to use the throttle to controll wheel spin.
Also, a feature I just love is the ability to store a large selection of fuel maps, allowing me to adjust boost or add/remove parts at any time and just select the fuel map that I want for the given situation. Now most systems offer this as a standard feature, however I would like to point out that alot of them make it INSANELY difficult to change the maps, and as far as I can tell, they do this needlessly. I really dont understand why Hondata thinks its nessisary to stop short of giving me a full physical just to switch fuel maps, so this is another thing to look at before picking a system.
Finally compatibility is something to think about when choosing your ecu. The system may work great on your car, but it is always nice to have a system that works good on all or most cars. This is why I highly recommend major companies like Apexi, Hondata and such because you know that they made the unit with the intension of systems capatibility with a large range of vehicles.
::MOST RECENT UPDATE::
Alright, so now on to upgrading your fuel system. Although the components listed in this section are very important to the operation of your turbo engine, it is actually one of the least complicated systems to understand. In fact, I could just as well list specific parts to use, as most any application will be about the same. The only real differences would be between Carburated and Fuel Injected systems. Beyond that, the various fuel injected systems are all pretty similar. Even Direct Injection, Port Injection, and Throttle Body Injection all operate so similarly, at least in the parts they use, that they would almost be interchangable. However, I'm lazy, so I'll just let you know what to upgrade and what to leave alone.
Basically, the when upgrading your fuel system, it is easiest to do it all in one go. Just think about the fuel flow through your engine, and start adding up how much power you can make with those parts before they will need to be replaced, and you will get an idea of what you will have to do. Basically, your findings should be something like this. Fuel is drawn by the fuel pump, so if the fuel pump cant pump enough fuel, you need a stronger pump. Next the lines the fuel is drawn through must be big enough to flow the fuel you will need without creating to much resistance pressure. If you need bigger lines, its easiest to do that when you change out the pump (you wont ever find an application where the stock fuel lines will be to small to work with a stock pump). Next the fuel filter must be equally high flowing, simlply changing it more regularly is the best thing you can do to keep it from being restrictive. Next the fuel rail must be able to store enough fuel for the injectors without running low on pressure. Then the injectors must be large enough to spray enough fuel, and the pressure regulator (if your vehicle has one) must be able to accurately meter pressure.
As far as upgrades go, I will say that an aftermarket fuel pump should be put on ANY car that adds more than 50% power up from stock. That means if you turbo a non-turbo car, you will need an aftermarket pump. Walbro makes a 255 Lph unit that is cheap ($70) and will give most engines more fuel than they will ever need. It is also avialable for a huge range of applications. You will most likely want to either adjust the stock fuel pressure with an adjustable fuel pressure regulator, or add larger injectors with a retuned fuel map to flow more fuel. As far as injectors go, pretty much any factory or aftermarket unit out there uses the same electrical connector, making junkyard upgrades easy. The only things you will need to make most any injector work on your car, is a resistor built into the wiring harness to make sure they get the correct amount of volts, and the correct O-rings to make them seal properly. You may need to also port your injector port holes to allow them to fit the manifold (if that is where they are located).
Now you wont always need to upgrade injectors to get more fuel, as an adjustable fuel pressure regulator can just turn up your fuel pressure when it reads boost, which is actually a pretty good system for people running a low budget. Another method is to use an AFC (air/fuel controller) Such as the highly used and highly recommended Apexi S-AFC. This will allow you to tell your injectors to inject more fuel when you want them to. However, if it turns out your stock fuel injectors DO need to be replaced, than you will need to use this AFC to tell the injectors what to do. This style of fuel managment falls under the catagory of piggy-back tuning. This means that the stock ECU is doing its thing, totaly oblivious to any mods you have done, and the secondary tunning device is making the changes you need.
Another thing you should get to moniter your fuel system is an Air/Fuel ratio gauge, or a Stoichiometric gauge. This will read your O2 sensor and tell you if you are running rich, lean or just right. For almost all turbo applications, you will want to run slightly rich on full throttle to leave a safety barrier, unless you like living dangerously (and broke). That is basically it for the fuel system components, other than some tuning tips (which I will get to next) and some other advanced principles (which will be covered later on, with all the other really complicated stuff). Untill then just remember that as long as you can get enough fuel for your engine to be happy, that you are doing ok.
Well, I will cover alot of the advanced fuel system tuning aspects later, when I have more time to get into the specifics of how to map out a fuel system for boost and how to use wide band o2 sensors and such, but for now, here are a few things to know.
First, just because an engine is running boost, does not mean it suddenly forgo's the rules of basic engines. Running rich will still kill power. That means that, despite its safety advantages, a properly running fuel system will make more power. A good example is a car that runs just slightly rich at idle but sounds like junk and backfires when spooling the turbo. Im going to give this next statement its own line. Its that important, so remember it.
The Absolute most common mistake people make when building up an engine, is getting lazy with engine management. :!: A car does not always equal the sum of its parts :!: It is very easy for things to go wrong, if the parts do not work together in harmony. Every single time I see a tuner car get tested that has been constructed just days before and has not had time for fine tuning, it ends up either blowing up or running like crap. Spending some good quality time with an o2 sensor, a lap top and a tuning program may seem boring, but it is one of the most important steps, and sadly one of the most overlooked. Any backfires, black smoke, soot, smells or wierd sounds / vibrations that come from your engine that are caused by bad tuning is power that could be making your car go faster.
Later when I get into turbo exducer flow charicteristics and calculated wastegate flow pressure percentages vs actual, you will laugh at how much work some people put into a carefully thought out system, only to have a car that runs like shit because the cam was to lumpy, or the timing has to much duration, or they run overly rich at mid-range RPM :roll: . So just keep this in mind when tuning your car. Leave some room for safety, but dont just take a singular stab at it. Everytime you think your car might have an issue, spend some time checking it out. After a few months of driving and tweaking, you can work most of the bugs out to the point where the car will feel like factory (just alot faster, well, hopefully).
Alright, well the last thing I'm going to cover before I move onto the next section is turbo upgrades. Now there is alot more I could cover on factory turbo cars (such as cooling systems, which I just might add something on later) but for the most part anything else I said here would be repeated later on when I cover building a custom turbo sytem, and building an engine for a turbo application.
Seeing as this is still in the 'intro' into turbochargers, Im not going to get too specific, but I will talk about what you will need to look for when picking an upgrade turbo, how far you should push your stock unit, and when to know to upgrade.
The first thing to mention is that you need to establish your goals from the begining if you only want to buy one turbo. If you just want 300 hp for now, but later decide you want more thats fine, but just keep in mind that setting realistic goals on what you want to do is very important with turbo chargers. Keep in mind a 800 Hp VW is great for internet bragging and Magazine covers, but pretty much useless and boring in the real world. So before you pick your turbo, decide what you want to do. Do you want to run fast in the 1/4 mile, or do you want to do track driving? Do you want a set up that will be more fun to drive, or more for impressiveness and bragging rights.
Another thing that you must understand is that the way people experience speed is relative. In english, that means that going from your pontiac sunfire to a Corvette would most likely make you crap your pants. However, if you drive a tuned Supra everyday, it wont feel that quick. What I'm trying to get at is that when you first start throwing the boost at your car, it will feel fast. In fact it should feel very very fast, if you do it right. But over time you might think "is my car getting slower?" or "it doesn't feel as strong as it used to..." mean while your passenger is covering their eyes and wetting themselves. No matter how monstrously fast your car is, it will evently feel normal to you if you drive it everyday. Keep that in mind when you're selecting mods. Buying 660cc instead of 540cc injectors might cost you an extra $50 now, but could save you hundreds later if you want a little bigger turbo. On a side note, turbo lag has a similar effect. When you first start driving a turbo car even the slightest delay in throttle responce might discust you, but after a few years, you find yourself thinking "hmmm 5500-7000RPM of full boost isnt THAT bad...." and you'd be wrong, but thats not important.
Now, in the last 18 months or so, the automotive world has been blessed with the quality of stock turbos that have been put on cars such as the SRT-4, EVO, WRX/STI, and others. They have a little more headroom for expansion than some of the turbos of the past decade. Of mention amoung these would be any T-25 equiped car (2g DSM's, S-13/14 SR20DET's) and 1.8T audi/VW engines. SAAB turbo cars of late also carry the title of micro turbo. All of these cars and engines use turbos so small, there is not alot of performance left to squeeze out of them in stock form. Although you can get away with a little extra boost, and a little more with some higher octain gas, these tiny units are so small that pushing them (or any turbo) past its operating range will lead to turbo failure very very quickly.
Garrett units such as T28's, T3's and T4's or almost anything sporting a GT series name, will have some more headroom for power built into them. Just beware of turbos of T3 design that use microscopic impeller fins (the fins on the intake compressor) as they tend to peak out at 15 psi. Do some research and find out how far you can push your turbo before it turns dead, and just see what people are using for upgrades and why.
Now is as good a time as any to mention that being part of an online community of people with the same car as you is always a good idea before any project. Being able to talk to someone who has been where you havn't is an invaluable tool to have. I should have mentioned this earlier, but better late then never, no? (then again if you're reading this, chances are you're no stranger to the internet, so you most likely have already done this).
When picking a turbo to upgrade to, make sure its a unit that will hit your power goal with some room to spare. In other words, dont pick a turbo thats going to be pushing as much boost as it can all the time, thats not good for efficiency. Look for a turbo that will do what you want and still run cool and efficiently during street driving. I will get into how to match a turbo for your car later on, but for now, keep this in mind. A car with less displacement will want a Turbine wheel with less mass and size, and an exhaust housing with smaller passages for good spool. You can get away with running a larger compressor without a big lag penalty if you size your housings right. Basically, a stanard t3/t4 lay out is perfect for 4 cylinder engines because it allows you to push alot of air efficiently while still having decent spool up. Also, full race manifolds (tubular equal legnth manifolds) will drastically help smaller engines make power and spool faster (some applications I've seen have gone from around 260 to 320, with no changes other than manifolds), so spending the extra $150 can really be worth it. So dont be affraid of buying a turbo that wont mount right up to the stock manifold. Just look at it this way. The stock manifold probably sucks anyway, just like your stock turbo, so upgrade both! :mrgreen:
Other than that, try and find a turbo that wont require re-routing of oil and water lines for the center section, as well as units that use the same fittings for those lines, to keep down the cost and complexity of installation. Fitment in tight spaces, as well as the outlet neck for the compressor housing (where it will connect to your intercooler pipe) can also be an issue.
:: Working on a very large opening into custom turbo applications, so check back soon for more info!::
If you are new to turbos I suggest you read on, or even if you think you know everything there is to know about them, I bet you'll be supprised with how complex finding the perfect matching turbo can be. However, sence there is so much to be said, I shall divide my prolonged rant into sections. I'll start off with the basics and go from there. I'll try and make large headers to let you know what section your in, to help vet's skip to the good stuff. Well if your ready to begin your turborific future, lets get going!
TURBO BASICS
If you think a turbocharger is something that fills your cell phone battery really fast, than this section is for you. First we are going to talk about the basic operation and function of a turbo, as well as some basic descriptions of how they are made up and why they are made the way they are. As always I am going to try and focus as much as possible on the most recent technology, rather than the most common or most avialable, simply because as time goes on this information will help you the most. Also, alot of people know what worked 10, 15 or 20 years ago, but very few stay up to date with the latest and greatest, so I find it best to stay current.
The first thing to know about turbochargers is this. They make power. :roll: Despite their many advantages, the most obvious one is that on any engine, in any condition they will increase your power. Basically what a turbo functions as is an Air Pump. In much the same way a water pump allows water to be taken from the water table 45 feet down, up to your sink, an air pump supplies more air than your engine could normally take in. Basically any naturally aspirated (N/A will be used as an abriviation. N/A means that the engine is not force inducted, and relies on engine vacuum created by the downward movement of the piston to pull in air) engine can only take in as much air as is allowed by how much vacuum force it can create. This is the main reason why bigger displacement engines make more power, because their swept area allows them to pull in more air for combustion. An air pump, such as a turbo compressor or a supercharger pushes air into the cylinder rather than making the engine have to pull it in. This alone makes power (example: try jogging for a while, then try jogging with an air mask on. The supply of air effortlessly flowwing into your lounges make it alot easier to keep jogging) however, as far as thermodynamics are conserned, it only retrieves the power that is otherwise lost by the engine having to work to pull in air. How a turbo really makes power is by compressing the air that enters the cylinder.
Compressed intake air is refered to as 'boost'. It is ushally rated in either BAR (a reading of a numerical value starting a 0 for atmospheric and increasing upwards. At 1 Bar the pressure is 14.7 psi, or 2 times atmosphereic pressure. Basically 1 Bar is one atmosphere of pressure.) or PSI (pounds per square inch). What this means is that the density of the air going into the engine is increased to add more power. What that means, is that the molecules of intake air are pressed closer together, so that for the same volume of air going into the engine, more air is contained in the cylinder, giving more oxygen for combustion. Add more fuel to burn with the extra air, and you get more power.
Now, that was rather basic information, only my lack of useable vocabulary probably made it sound like rocket science. But assuming that you now understand why a turbo makes power, its time to explain how a turbo goes about making it. You see there are not very many methods of which to add power to an engine. Sure there are alot of things you can do to make it more powerfull, but really you are only doing one of three things. The first is making it easier for the engine to operate, thereby freeing up previously lost horsepower. This would include fuel system modifications (that dont include adding more fuel to combustion), ignition system add ons, head work and cams, any form of porting, intake/exhaust mods or anything that makes power on a N/A engine. The next is forced induction which includes turbo chargers, superchargers, electric air pumps, adding more fuel via fuel modifications, or vacuum pumps (otherwise known as exaust pumps, they have not been in production for over 70 years, but their function is basically to create a vacuum force in the exhaust system to help pull the intake air in rather than push it). The third method is chemical forced induction, such as nitrous oxide, which changes the intake substance from air to... something other than air (a something ushally containing more oxygen, because it wouldnt really make sence to force your engine to take like hydrogen or something..... unless you like broken stuff....)
Ok, so that was a bit off topic, but basically what im getting at is that there are not many ways to increase the power of an engine, because this is not a perfect world and the law of conservation of energy states that energy has to come from somewhere, and often things cost more energy to run than they make it. So just how does a turbocharger make power?
A turbocharger is basically an exhaust driven air pump, meaning it has one large housing with a turbine wheel inside (like you would find in a hydro-electric generator or those big wind power thingies.... ) that is being pushed on by the exhaust gasses, and another large housing with a compressor wheel, which is a shaped circular blade that uses the clearance between it and the housing to catch, move and compress the air going into the engine. The two wheels are connected via a shaft that makes them spin at the same speed. The exhaust turbine drives the air compressor forcing air into the engine. This is the means by which a turbo gets its power, and why they are so kick ass (highly technical term). Because they reuse the heat energy lost in the exhaust system, they are recovering already lost energy to make power, unlike other systems like superchargers that use engine power to make power. Here is a good picture showing the two housings.
http://img.photobucket.com/albums/v517/Adamk2424/turbo-parts.gif
Hopefully now you understand how a turbocharger works, as far as the basics. But before we head to the next section just a few more things to know about turbos and how they work. First off the center section of the turbo. This section contains the shaft, bearings, oil and coolant passages, carbon, coolant, air and oil seals, and often the housing hold down assemblies.
The shaft is a hard metal rod that connects the two wheels together and transmitts power from the exaust to the intake wheel. It spins on a set of bearings, which we will talk more about later. Not all turbos are water cooled, but most modern turbos use coolant as a method of controlling heat transfer from the exaust side to the intake side (in other words minimizing it) as well as prolonging the life of your bearings and housings. The oil passages provide lubrication for the shaft and bearings as well as helping to keep them cool. The carbon seals are metallic scrappers that help prevent carbon build up in the exhaust housing as well as carbon from entering the center housing and clogging in the oil. Coolant and oil seals are pretty self explainitory, and air seals keep the air in the compressor housing and not in the coolant or oil passages where it doesnt belong.
Other basic things about turbo charger systems are Intercoolers and Compressor Bypass valves or Blow of valves (BOV for short). Intercoolers go by many names, here are some of the most common: Aftercooler, Intake Air Coolers, Charge Air Coolers, FMIC (front mount intercooler), Intake Charge Heat Exchangers, or big shiney thing at the front of your car to get the girls to notice you... Blow off valves can be used for the same purpose (getting the girls that is) as they can be modified to be very loud. The basic Function of a BOV is to redirect air back into the intake side of the compressor before it reaches the thottle body, to prevent compressor surge on throttle lift. (more on this later) Intercoolers do exactly what they sound like they do. They cool the air going into the engine, because as we all know, cooler intake air = :mrgreen: . Here is a nifty picture showing basic construction of an intercooler.
http://img.photobucket.com/albums/v517/Adamk2424/hmt60203e.jpg
http://img.photobucket.com/albums/v517/Adamk2424/hmt60203g.jpg
Basiscally the air goes into one side, is directed through anyone of a number of tubes inside the intercooler, which are incontact with cooling fins. The hot air goes in, is cooled by the cold aluminium and comes out cooler. The aluminium gets hot, which is cooled by the outside air flowing over the cooling fins. Later I will talk more about other types of intercoolers, including air to water and water injection, but for now here is a picture showing the layout of your basic turbo system.
http://img.photobucket.com/albums/v517/Adamk2424/turbo-plumbing.gif
Now that the basics are out of the way, its time to get to it! Im not sure what order I should go in, but I think I will try to save the most complicated stuff for later on. So pick a subject and read on!
MAKING POWER WITH A TURBO VEHICLE
If your reading this, Im sure your not interested in turbos because of their awsome fuel economy, so lets get right to the good stuff. How to properly make power with a turbocharged engine. Although it is easiest to start with a stock engine made for boost, I will cover how to build and prep an engine for turbocharging.
First off, if your car comes stock turbocharged, you are on easy street. More power is just a trip to the hardware store away. However, the biggest problem with having instantly adjustable power is that people dont know when to call it quits, and over boost their engines. Doing proper research into what works or doesnt work for your application is a must! Always know what your doing, and the limits of every part on your car. This cannot be over emphized. Know what the limiting factor in your system is and leave a 15% barrier at all times. Respecting this limit will keep your parts working properly, because boost is no fun when its broken.
A good example is a 2nd generation DSM (eclipse, lazer, talon) with the turbo 4G63 engine. Rated at 210 hp stock with a tiny t-25 turbo, there is only a fair amount of room for increased power before you will need to upgrade turbos. However, that doesn't mean run out and get a new turbo right away. Know the limits of the parts on the car, and start with the weakest link. No point in turning up the boost when the stock BOV leaks, limiting your boost to 12 psi, when its already set at 14.7 from the factory.... simply replacing this unit on 2nd gen. DSM's adds an effective 3 psi and about 15 whp.
So once you determine what your goals are, and what stock parts on your car will work, its time to look at upgrades. Here is a list of some of the most basic things any turbo owner should get.
The first is a full new exhaust system. Turbos get their energy from the exhaust coming out of the head. However, the gasses have to go somewhere when they leave the turbo, and its hard to push gass out if it has no where to go. Freeing up back pressure is the easiest and most reliable way to make power in a turbocharged vehicle. A first generation DSM can make over 65 hp with simple exhaust work, on a stock car! For bang per buck, its hard to beat a good 3" or larger exaust system. Heres what parts you need to look for.
1) O2 sensor housing. This unit mounts to the back of the Exhaust housing of the turbo. Not all cars will have this separted unit, as some will have a one piece downpipe that connects the turbo to the cat. However, if your vehicle does have this unit its most likely horribly restrictive (unless its an Lancer Evolution, whos o2 housings are beautifully designed), and should be the first unit to be replaced.
2) Downpipe. The most important unit to replace, is the downpipe, as it is the first piece of tubing in the system. What makes it so special is all of the important things that take place before the exhaust goes through the cat. First the wastegate gasses, which will be either divorced or integrated (which I will cover later) must rejoin the exhaust before the cat. The basic rule on internal wastegates is the smoother the transition back into the exhaust the better. Waiting to rejoin the tubing after the first bend is ideal, but most units simply dump it into a wall at the face of the downpipe. This is horribly restrictive as well as possibly damaging to the turbo if you run into a lean condition. Allowing the wastegate gasses their own passage is what you really want, however a simple wall a few inches long separating it from standard exhaust gas flow is ok. Then allowing it to smoothly flow into one pipe helps keep back pressure down. Another important feature of the downpipe is that it must bend alot to reach from the turbo outlet to the cat. This means that its design and smoothness will have a major impact on the efficiency of the exhaust system. Elliminating kinks and bends in the stock system is where your power will be made here.
3) Cat back. From the catalitic converter back is called the cat back portion of the exhaust system and seeing as its the longest part, it is very important. Resonators are good for keeping the engine quiet, but kill power. My rule is, turbos work as effective exhaust mufflers already, killing loud pulses from the exhaust valves. So Straight pipes into smooth mufflers is my favorite, keeping back pressure to a minimum. Although your choice of exhaust systems make a huge difference in the sound of your N/A vehicle, turbo cars are less likely to totaly change sound from one system to another, so Its hard to recommend any one brand, but Im a fan of Greddy turbo exhaust systems, just because they do a good job at alot of systems for alot of cars without hugely expensive prices.
4) Catalytic Converter. Now, at least in america, it is required that you do not make any modifications to the factory catalytic converter if you want to drive on the streets. However, no will will ever notice if you put an after market high flow cat on. But even that is to much trouble for most people, so damn the environment, I recommend just running a straight pipe in place of the factory cat on turbo cars. You make so much power by taking the cat out, its hard for me to justify spending all that money for a high flow cat. You can always swap the cat back on for emissions anyway.
I will get into more factors that make power in the exhaust system when talking about making custom turbo systems in the next section. The next area to look at improving on your turbo car is the intake tract. Basically using the same principles as a n/a intake system, the larger the piping the better, the shorter the piping the better, and the cooler the intake air the better. Also dont forget a filter. Some people will tell you that you dont have to run a filter on a turbo vehicle. This is monumentally stupid. The same dirt that goes into the turbo is going into the engine. The only thing that could possible happen diffferntly is the dirt clogging in the turbo rather than in the oil in the engine, which isnt any better really. Ok, well yes turbo cars can get away with a little more particulate matter in the air, because their higher combustion temperatures will burn some of the heavier stuff that might get sucked in, however it is not enough of a factor to risk your engine or your turbo. If you want, just buy a $5 foam filter off ebay that come pre-made to mount to the compressor inlet of the turbo. It flows great and filters.... well... not so great, but it will keep everything large enough of concern out. A friend of mine once ran his car with no filter and got a stick thrown up from the road lodged in his turbo, which basically shattered the compressor wheel, so dont risk it.
My favorite intake method on a turbo car is just a 2 or 3 inch long aluminium pipe with a filter on the end that reaches away from the hot exhaust area to a cooler part of the engine bay. It doesnt need to be completely sealed off, just in a cooler part will help out. If your car has an air metering system such a DSM, Skyline or 300zx, you will need to build your intake system around this unit, unless you plan on going after market engine management, but I would see no reason to do that. These systems work great in my opinion. As compared to stock N/A cars, that freak out when they see boost, or have no idea what to do once you start changing the stock airflow charicteristics, these systems actually go, "alright he's flowing 234 cfm of air, looks like its about 68 degrees outside, lets give him an extra 2 degrees of pulse width on that injector pulse." Its a very good system for quickly adjusting boost levels.
Another thing about the intake tract on a turbo vehicle, is the intercooler. Intercoolers are a gift from heaven when it comes to running boost. Back in the less than impressive technology of the 1970s and early 1980s, more and more cars were coming turbo charged from the factory. The problem was that the huge heat that they generated for a number of factors (one is that they used horribly in effecient turbos that made more heat than they did power, another is that they did not water cool their turbos, another yet is they did not yet understand that the flow charicteristics of the exhaust housing greatly determines the overall performance of a turbo on an engine, and using... well I have not gotten to this stuff yet, but its very complicated so I will get to it later), ment that they were only lasting around 60-70,000 miles before they would die. Now back then this wasnt to good, but it wasnt that bad either. Today this would be 100% unacceptable from a new car. So, they started thinking of ways to try and cut down on the intake temperatures.
Now dont get me wrong, Intercoolers are nothing new. The have been around for almost as long as the turbocharger, however its one of those things that makes you wonder, "why didnt they do that earlier...." like finding out that the lead in gas is collecting in the ground water, putting something to reduce the intake temp. on a turbo car falls under the catagory of 'duh'. Today you wont find a factory turbo car with no intercooler (at least I dont think you will, I just know someone will generate a picture from somewhere), but because of the improvements in turbocharger design and construction, it is again possible to make a low boost turbo system with no intercooler. Now I'm not going to recommend anyone do this, but their are benifits having no intercooler, such as increased throttle responce, higher compressor efficientcy (because there is no pressure drop like you would get in an intercooled system) reduced cost and complexity, and smaller overall packaging making it easier to fit in tight places. However, even a small intercooler does wonders for keeping down intake temps, as long as it has proper air flow.
There are basically two types of intercoolers. Air to Air and Air to Liquid. Air to Air intercoolers work like the basic intercooler I described in 'turbo basics'. They send air from the turbo through in the inside, while air from outside blows across the fins like a radiator, and cools the intake air down. This then goes into the throttle body cooler and happier. Now there are a few different types of air to air systems but they all basically work the same. Some intercoolers are fin rack style (most stock units are of this design), and most aftermarket units are bar and plate style. (Basically alternating possitioning of the plates to create passages on the inside for the air to travel in, then filling in the gaps with fins for cooling.) I prefer bar and plate, because of its smoother flow and lower pressure drop, however as far as actually cooling the air, the stock units will work better (dont argue it, its true). Air to Liquid or Air to Water intercoolers work by the air going through an intercooler that is surrounded with cooling water rather than air. Air to Liquid intercoolers however have alot of advantages compared to air to air, such as the ability to cool the air much faster, and to lower the air to temps below that of room temp. by running ice water or other cold liquids in the system. Also because you only need to keep the water cool by running a heat exchanger for the water in the system (similar to an external oil cooler) you can place the unit much closer to the throttle body, meaning less piping which means less air to compress to get on boost, which means faster spool up.
However, there are some major disadvatages to water cooling systems, such as complexity and cost. They are very expensive and extremely hard to properly route. As you will need a tank for the water, a fill area with a pressure holding cap, water lines, a heat exchanger, a pump to flow the water through the system, the cooler its self and a method of removing air from the system (often a sprayer nozzle). The other major downfall to this system is that, where an aluminium FMIC will never heat up to much as long as it has good airflow, a water system has a harder time keeping its self cool during prolonged driving. For drag racing this is not a problem and I highly recommend water intercoolers for their ability to make more power, colder air and to cause less pressure drop, but for daily driving or for track racing, an air to air unit is preferable.
Another important piece of the intake for a turbo system is the compressor bypass valve, or BOV. When it comes to stock units, the first generation DSM unit is about as good as it gets, setting the standard by which all valves are measured against even to this day. Skylines, Rx-7's, Evos and S-15 silvias all use units almost directly copied from the first gen. eclipse/talon/lazer. Strangely then, why Mitsubishi decided to replace this outstanding unit with a crappy piece of plastic crap on the second generation DSM, I have no idea. But basically, there are only 3 types of BOVs that you will see out there. The first type, such as the 1g dsm, is called a lift valve, which basically means it uses spring pressure on both sides, and uses vacuum pressure to open the valve. This is identical in its operation to the other most common type of valve, the poppet valve. Basically they both use a spring with a vacuum port at the top of the spring chamber, so that on throttle lift, the negative pressure (vacuum) that is caused by the throttle plate going shut, over comes spring pressure and opens the valve, which basically just opens a loop back to the start of the intake system. Where the lift valve is different is that their is a second spring on the bottom of the valve to help push it back up faster when you get back on the gas, as well as helping to hold the valve closed tighter when under boost. This is the main problem with poppet valves. They tend to leak under high boost conditions because they have no secondary support springs to help hold the valve shut. This is no problem on well built aluminium aftermarket units with heavy duty springs and well sealed pistons in the BOV cylinder, but on stock plastic units with wimpy springs, leaks are quiet frequent.
The only other style of valve that I am aware of, is the Sequential unit. Basically this is a Lift valve with a timed push rod in the center that actuates a secondary port in the air out side of the housing. In english, that means that when you let off the gas and the BOV activates, it starts with the spring letting just enough air out to keep the turbo from surging, but the main body of the valve is still closed, holding in as much boost pressure as possible. After about .5-2 seconds after vacuum was first detected, if the valve is still in vacuum the secondary spring actuates and opens the main piston. This is used to keep boost pressure from dropping during shifts. They work very well, however many of the valves in the market that claim to be 'sequential' are acutally just lift valves, such as the HKS SSQ BOV, which besides being a very long list of Letters, is just a standard poppet valve that lays sideways and sounds cool.
Before I continue, it has been pointed out that I need to explain the difference between a dump valve and a bypass valve, so here goes. Basically, a BOV (Blow Off Valve) will allow the compressed intake air to vent into the engine bay whereas a CBV (Compressor Bypass Valve) will return the air into the intake side of the compressor. As far as a performance stand point, there is very little reason to use a BOV over a CBV. A bypass style valve makes the turbo work alot less hard on re-spool because the air going in is already partially compressed, as well as being pre-cooled by the intercooler (ok not as cool as ambient air, but because its already compressed it will be cooler coming out the other side than ambient air). Also, on many systems that use a CBV in factory form coupled with a mass airflow meter, like a DSM or Skyline etc... the stock ecu will predict that the air being vented from the valve will be re-entering the intake system rather than being vented to atmosphere. Placing a BOV on this type of system will cause your car to run temporarily lean on throttle lift, so using an AFC (air fuel controller) to adjust this may be nessisary.
As for BOV's advantages, the only one I can think of is the sound. Where as a CBV is very quiet, and difficult to hear unless your really listening for it, a BOV makes alot of racket. This is the primary reason why people use BOV's over CBV's. One more thing to mention, is that on vent to atmosphere valves, make sure that A) the horn of the valve is not facing to the sky, which could cause water to be pooled in the opening and get inside the valve body, causing wear and failure, and B) If it is rather dusty in your area using a filter on the end of your BOV is a good idea, as it sucks a little air back into the intake before it has time to close.
Ok, after intake and exhaust on a turbo vehicle, the next thing you should look at is your fuel system. Obvioulsy, the fuel system is very important to any engine setup, but on a turbo vehicle things become alot more complicated. To start I will talk a little about how a stock turbo fuel system works, before moving on to aftermarket systems, upgrades and parts, and finally some advice about the fuel system and tunning.
Ok, so most stock fuel systems on turbo vehicles operate on this philosophy, 'turbo cars need a big safety margin.' That means that they need to run rich most of the time, to prevent from ever going lean. And just for the record, lean engine conditions + boost = expensive broken parts. This means that there is some power to be made by tweaking the system and leaning it out in places where its a little to rich for its own good. Im not going to get into that just yet, but some cars such as the Evo8 can make over 30 hp with no other mods, just from a good ecu tune. (for more info check out Vishnu performance at http://www.vishnutuning.com/ , normally I wouldnt plug a company, but they are one of my favorites).
The reason why I wont be talking about ECU tunning just yet is this section is about stock ecus, and no one is going to thin out a stock ecu on a turbo car, when they can just turn up the boost rahter than reducing the fuel. This obviuosly achieves the same result while making more power. Now, the ecu will of coarse compensate for the extra boost with more fuel, but as you start to push the limits of your stock fuel system, you will need to start upgrading parts. But anwyay, back to stock. Most turbo cars are going to use a honeycomb style mass air flow meter to read how much air is entering the engine (some use an air flow sensor before the throttle body to read boost as well, on top of air flow) and adjust fuel accordingly. This is good for us because this means we can pump the boost without having to tell the engine to add more fuel. Now, if you were paying attention, I said MOST turbo cars use this system. By that I ment that most modern cars have gone to less tunning friendly systems. A good example is the Dodge SRT-4. The car its self is possibly the best performance buy of all time, however because of its wierd exhaust manifold design (which uses the manifold and turbo exhaust housing as a single casting with an exhaust arm aka o2 sensor housing that is shaped so wierdly that almost no after market companies can make units that work better and dont leak) and crazy engine management system, the car is a tunning nightmare. Now dodge does offer factory perfomance stuff, but if I bought one, the first thing I would do is put in a completely new aftermarket computer. Heres why.
The SRT-4's method of controlling how much boost the engine is running is based on the known flow charicteristics of a stock SRT-4 engine. This means that if the engine reads the temp at 75 degrees and the rpm at 5100 and the turbo at full spool, it will open the wastegate (example only not actuall figures) 83% to keep it at the correct amount of boost, and inject 219 cc's of fuel for combustion. This is all well and good, untill you start wanting more power. Ok, so say you put an aftermarket exaust on it. "its just piping" you think, it shouldn't affect anything much with the engine. Normally you'd be right, but unfortunately because changing the backpressure by 3 psi completely changes the air flow charicteristics of the engine, and now when you give it 60% throttle the turbo spools up alot easier because it has to work less hard to push the exhaust gas. So now you have to much boost and a computer that is lost as to what is going on, making your engine run lean and knock. The Ecu see's the knock and puts you into dumbass mode, otherwise known as limp home or low power mode.
Now some people will ask "Why do they do it this way? If it only causes problems, why dont they stick with the what worked in the past?" Well the anwser is two fold. First, it doenst only cause problems. This method of engine management works better at reducing emissions, increasing fuel economy, and preventing damage to the engine. Also, the car industry does not want people to modify the cars they sell (at least, some of them dont.) When people start turning up the boost and making more power, things break, and because people lie, alot of parts get covered under warrentee, and the company loses money. By making it more difficult to tune, they save costs down the road. But dodge found an even better way to do it. They made a car that they knew everyone would want to tune, and gave it an impossibly difficult engine management system to crack. Then they offer us THEIR parts to make power. Its a brilliant idea, even if I think the parts they offer suck.
But personally I dont care If my exhaust is killing pengiuns and chipmonks, I want more boost. So if your looking at seriosly modifiying your car, either stick with the stuff a few years old, or look for aftermarket ecus. (the exception to this rule is subaru/mitsubishi, they seem to WANT us to blow up our cars, and still sell the good stuff).
Ok, aftermarket management. I wont be getting into this too deep, as it will be covered in great detail in the custom turbo car section later. But for now, just some basics about what to look for.
The most important thing to think about when looking at aftermarket controll units, is there tuneability. What do they let you change, and what options do they offer. Do they have dual stage boost controll settings? Do they offer multiple selectable fuel maps? And what are you going to have to do to get those maps? Does this company offer pre-tuned maps for download on line? Or will you have to take your car to a shop to get tunned? Things like this will be your biggest consern when picking an engine management. All systems should do their job of suppling enough fuel at the right time to prevent bad things happening, while still keeping your bumper from catching on fire and making you go through a gallon a mile of fuel. Other than that, its the options they offer that really make the difference. So let me explain what some of those options are.
First off, it is always a good idea to find an ecu that has pre-made maps avialable for your application. As I stated before, I like Vishnu tunning for evo's and wrx's, because they offer a huge range of pre-made maps for download on their web site, and I've seen alot of heavy hitters running their systems. Having to take your car down to a shop to get tunned not only takes alot of time, but is very costly as well. And speaking from experience, the extra expense is not worth the slight performance pay off. Dont get me wrong, a custom tune will almost always be better, but if your asking if its worth it, Id almost always say no, if pre-made maps are avialable.
Another feature to look for is dual stage boost settings. Although this option used to only be offered on the more expensive ECU systems, it has been becoming more and more common and when I checked just prior to this article, it seems that most of the companies out there today offer it as an option. However if you asked me of its usefullness, Id tell you not to bother unless you were having traction controll issues. Basically what a dual stage system does, is limits your boost in a certain gear to keep you from just spinning the wheels. This means you could set up your car to run 16 psi in first, 21 in second and max boost in all the following gears to help you get down the track faster. My problem with this is it doesnt offer me the flexibility I would want in track or street driving. For the drag strip, this can be an invaluable tool, but for my purposes, I prefer to use the throttle to controll wheel spin.
Also, a feature I just love is the ability to store a large selection of fuel maps, allowing me to adjust boost or add/remove parts at any time and just select the fuel map that I want for the given situation. Now most systems offer this as a standard feature, however I would like to point out that alot of them make it INSANELY difficult to change the maps, and as far as I can tell, they do this needlessly. I really dont understand why Hondata thinks its nessisary to stop short of giving me a full physical just to switch fuel maps, so this is another thing to look at before picking a system.
Finally compatibility is something to think about when choosing your ecu. The system may work great on your car, but it is always nice to have a system that works good on all or most cars. This is why I highly recommend major companies like Apexi, Hondata and such because you know that they made the unit with the intension of systems capatibility with a large range of vehicles.
::MOST RECENT UPDATE::
Alright, so now on to upgrading your fuel system. Although the components listed in this section are very important to the operation of your turbo engine, it is actually one of the least complicated systems to understand. In fact, I could just as well list specific parts to use, as most any application will be about the same. The only real differences would be between Carburated and Fuel Injected systems. Beyond that, the various fuel injected systems are all pretty similar. Even Direct Injection, Port Injection, and Throttle Body Injection all operate so similarly, at least in the parts they use, that they would almost be interchangable. However, I'm lazy, so I'll just let you know what to upgrade and what to leave alone.
Basically, the when upgrading your fuel system, it is easiest to do it all in one go. Just think about the fuel flow through your engine, and start adding up how much power you can make with those parts before they will need to be replaced, and you will get an idea of what you will have to do. Basically, your findings should be something like this. Fuel is drawn by the fuel pump, so if the fuel pump cant pump enough fuel, you need a stronger pump. Next the lines the fuel is drawn through must be big enough to flow the fuel you will need without creating to much resistance pressure. If you need bigger lines, its easiest to do that when you change out the pump (you wont ever find an application where the stock fuel lines will be to small to work with a stock pump). Next the fuel filter must be equally high flowing, simlply changing it more regularly is the best thing you can do to keep it from being restrictive. Next the fuel rail must be able to store enough fuel for the injectors without running low on pressure. Then the injectors must be large enough to spray enough fuel, and the pressure regulator (if your vehicle has one) must be able to accurately meter pressure.
As far as upgrades go, I will say that an aftermarket fuel pump should be put on ANY car that adds more than 50% power up from stock. That means if you turbo a non-turbo car, you will need an aftermarket pump. Walbro makes a 255 Lph unit that is cheap ($70) and will give most engines more fuel than they will ever need. It is also avialable for a huge range of applications. You will most likely want to either adjust the stock fuel pressure with an adjustable fuel pressure regulator, or add larger injectors with a retuned fuel map to flow more fuel. As far as injectors go, pretty much any factory or aftermarket unit out there uses the same electrical connector, making junkyard upgrades easy. The only things you will need to make most any injector work on your car, is a resistor built into the wiring harness to make sure they get the correct amount of volts, and the correct O-rings to make them seal properly. You may need to also port your injector port holes to allow them to fit the manifold (if that is where they are located).
Now you wont always need to upgrade injectors to get more fuel, as an adjustable fuel pressure regulator can just turn up your fuel pressure when it reads boost, which is actually a pretty good system for people running a low budget. Another method is to use an AFC (air/fuel controller) Such as the highly used and highly recommended Apexi S-AFC. This will allow you to tell your injectors to inject more fuel when you want them to. However, if it turns out your stock fuel injectors DO need to be replaced, than you will need to use this AFC to tell the injectors what to do. This style of fuel managment falls under the catagory of piggy-back tuning. This means that the stock ECU is doing its thing, totaly oblivious to any mods you have done, and the secondary tunning device is making the changes you need.
Another thing you should get to moniter your fuel system is an Air/Fuel ratio gauge, or a Stoichiometric gauge. This will read your O2 sensor and tell you if you are running rich, lean or just right. For almost all turbo applications, you will want to run slightly rich on full throttle to leave a safety barrier, unless you like living dangerously (and broke). That is basically it for the fuel system components, other than some tuning tips (which I will get to next) and some other advanced principles (which will be covered later on, with all the other really complicated stuff). Untill then just remember that as long as you can get enough fuel for your engine to be happy, that you are doing ok.
Well, I will cover alot of the advanced fuel system tuning aspects later, when I have more time to get into the specifics of how to map out a fuel system for boost and how to use wide band o2 sensors and such, but for now, here are a few things to know.
First, just because an engine is running boost, does not mean it suddenly forgo's the rules of basic engines. Running rich will still kill power. That means that, despite its safety advantages, a properly running fuel system will make more power. A good example is a car that runs just slightly rich at idle but sounds like junk and backfires when spooling the turbo. Im going to give this next statement its own line. Its that important, so remember it.
The Absolute most common mistake people make when building up an engine, is getting lazy with engine management. :!: A car does not always equal the sum of its parts :!: It is very easy for things to go wrong, if the parts do not work together in harmony. Every single time I see a tuner car get tested that has been constructed just days before and has not had time for fine tuning, it ends up either blowing up or running like crap. Spending some good quality time with an o2 sensor, a lap top and a tuning program may seem boring, but it is one of the most important steps, and sadly one of the most overlooked. Any backfires, black smoke, soot, smells or wierd sounds / vibrations that come from your engine that are caused by bad tuning is power that could be making your car go faster.
Later when I get into turbo exducer flow charicteristics and calculated wastegate flow pressure percentages vs actual, you will laugh at how much work some people put into a carefully thought out system, only to have a car that runs like shit because the cam was to lumpy, or the timing has to much duration, or they run overly rich at mid-range RPM :roll: . So just keep this in mind when tuning your car. Leave some room for safety, but dont just take a singular stab at it. Everytime you think your car might have an issue, spend some time checking it out. After a few months of driving and tweaking, you can work most of the bugs out to the point where the car will feel like factory (just alot faster, well, hopefully).
Alright, well the last thing I'm going to cover before I move onto the next section is turbo upgrades. Now there is alot more I could cover on factory turbo cars (such as cooling systems, which I just might add something on later) but for the most part anything else I said here would be repeated later on when I cover building a custom turbo sytem, and building an engine for a turbo application.
Seeing as this is still in the 'intro' into turbochargers, Im not going to get too specific, but I will talk about what you will need to look for when picking an upgrade turbo, how far you should push your stock unit, and when to know to upgrade.
The first thing to mention is that you need to establish your goals from the begining if you only want to buy one turbo. If you just want 300 hp for now, but later decide you want more thats fine, but just keep in mind that setting realistic goals on what you want to do is very important with turbo chargers. Keep in mind a 800 Hp VW is great for internet bragging and Magazine covers, but pretty much useless and boring in the real world. So before you pick your turbo, decide what you want to do. Do you want to run fast in the 1/4 mile, or do you want to do track driving? Do you want a set up that will be more fun to drive, or more for impressiveness and bragging rights.
Another thing that you must understand is that the way people experience speed is relative. In english, that means that going from your pontiac sunfire to a Corvette would most likely make you crap your pants. However, if you drive a tuned Supra everyday, it wont feel that quick. What I'm trying to get at is that when you first start throwing the boost at your car, it will feel fast. In fact it should feel very very fast, if you do it right. But over time you might think "is my car getting slower?" or "it doesn't feel as strong as it used to..." mean while your passenger is covering their eyes and wetting themselves. No matter how monstrously fast your car is, it will evently feel normal to you if you drive it everyday. Keep that in mind when you're selecting mods. Buying 660cc instead of 540cc injectors might cost you an extra $50 now, but could save you hundreds later if you want a little bigger turbo. On a side note, turbo lag has a similar effect. When you first start driving a turbo car even the slightest delay in throttle responce might discust you, but after a few years, you find yourself thinking "hmmm 5500-7000RPM of full boost isnt THAT bad...." and you'd be wrong, but thats not important.
Now, in the last 18 months or so, the automotive world has been blessed with the quality of stock turbos that have been put on cars such as the SRT-4, EVO, WRX/STI, and others. They have a little more headroom for expansion than some of the turbos of the past decade. Of mention amoung these would be any T-25 equiped car (2g DSM's, S-13/14 SR20DET's) and 1.8T audi/VW engines. SAAB turbo cars of late also carry the title of micro turbo. All of these cars and engines use turbos so small, there is not alot of performance left to squeeze out of them in stock form. Although you can get away with a little extra boost, and a little more with some higher octain gas, these tiny units are so small that pushing them (or any turbo) past its operating range will lead to turbo failure very very quickly.
Garrett units such as T28's, T3's and T4's or almost anything sporting a GT series name, will have some more headroom for power built into them. Just beware of turbos of T3 design that use microscopic impeller fins (the fins on the intake compressor) as they tend to peak out at 15 psi. Do some research and find out how far you can push your turbo before it turns dead, and just see what people are using for upgrades and why.
Now is as good a time as any to mention that being part of an online community of people with the same car as you is always a good idea before any project. Being able to talk to someone who has been where you havn't is an invaluable tool to have. I should have mentioned this earlier, but better late then never, no? (then again if you're reading this, chances are you're no stranger to the internet, so you most likely have already done this).
When picking a turbo to upgrade to, make sure its a unit that will hit your power goal with some room to spare. In other words, dont pick a turbo thats going to be pushing as much boost as it can all the time, thats not good for efficiency. Look for a turbo that will do what you want and still run cool and efficiently during street driving. I will get into how to match a turbo for your car later on, but for now, keep this in mind. A car with less displacement will want a Turbine wheel with less mass and size, and an exhaust housing with smaller passages for good spool. You can get away with running a larger compressor without a big lag penalty if you size your housings right. Basically, a stanard t3/t4 lay out is perfect for 4 cylinder engines because it allows you to push alot of air efficiently while still having decent spool up. Also, full race manifolds (tubular equal legnth manifolds) will drastically help smaller engines make power and spool faster (some applications I've seen have gone from around 260 to 320, with no changes other than manifolds), so spending the extra $150 can really be worth it. So dont be affraid of buying a turbo that wont mount right up to the stock manifold. Just look at it this way. The stock manifold probably sucks anyway, just like your stock turbo, so upgrade both! :mrgreen:
Other than that, try and find a turbo that wont require re-routing of oil and water lines for the center section, as well as units that use the same fittings for those lines, to keep down the cost and complexity of installation. Fitment in tight spaces, as well as the outlet neck for the compressor housing (where it will connect to your intercooler pipe) can also be an issue.
:: Working on a very large opening into custom turbo applications, so check back soon for more info!::