Changing compression ratio

[sergei_dekker85]

any ideas on how to change the compression ratio W/O changing pistons,crankshafts and valves??

[ZfrkS62]

thinner head gasket is the first thing that comes to mind. you could always try decking the head or swapping heads with a different year with a higher C.R.

[sergei_dekker85]

Well My Engine is a QR25DE....relatively new engine to the market(same one used in the B15 sentra SER spec-V) plan to change it to 11.3:1 currently running it at 8.9:1 what about grinding the block? heard of it?

[ZfrkS62]

if you're going to do that, you need to be royally carefull not to overheat. it won't take much to warp your block once you start decking. and if you're going to do that, you may as well change your crank since you'll have to disassemble the engine to send the block and head to the machine shop. (CNC machining locates the cylinder bores off the main journals)
you can't change compression as much as you want to with out changing either the crank or the pistons.

[T-Bird]

Well My Engine is a QR25DE....relatively new engine to the market(same one used in the B15 sentra SER spec-V) plan to change it to 11.3:1 currently running it at 8.9:1 what about grinding the block? heard of it?

well that's kind of what he meant by the decking the heads. You have to make sure if you do any of this that it wont cause the valves to hit the cylinders which can cause some major problems. so yes you could take some metal off the block and or heads and a thinner gasket but going up that high of compression without replacing any large components doesn't sound like a cheap or easy job.

[lev_p]

First, for greater compression ratio you grind off the head, not the block. Have it made by specialists, otherwise you may grind too much or not even. You may also need to reprogramm engine's ECU, or get another one. When you are at it, have also some porting done - doesn't cost much, but makes some improvements.
After you do that, use only the best fuel (highest octane ratio) you find - otherwise it'll detonate.
Me and a lot of my friends have done it on our cars - and now 12 year old French cars drive like mad :P

P.S. You might need to have a new head gasket custom-made from thin stainless steel...

[sergei_dekker85]

Hmm...ot bad eh...11.5:1 ratio SUV.... :lol: :lol: :lol: Best way in my country 2 gain power W/O getting into trouble with the law (TCing and SCing is illegal in my country FYI)

[ZfrkS62]

(TCing and SCing is illegal in my country FYI)


that's gotta be the dumbest thing i've heard since finding out norway gives out fines for modded mopeds :?

[T-Bird]

First, for greater compression ratio you grind off the head, not the block. Have it made by specialists, otherwise you may grind too much or not even. You may also need to reprogramm engine's ECU, or get another one. When you are at it, have also some porting done - doesn't cost much, but makes some improvements.
After you do that, use only the best fuel (highest octane ratio) you find - otherwise it'll detonate.
Me and a lot of my friends have done it on our cars - and now 12 year old French cars drive like mad :P

P.S. You might need to have a new head gasket custom-made from thin stainless steel...

Not always the case on some head designs you cannot take very much off of them or you will affect the width of the cylinder and the fact that some have such low clearance heads in order to save room it would be quicker and easier to deck the block. You rarely would have to change the computer for compression ratio changes since there are no sensors for compression ratio last time I checked. And last time I checked if you take your heads to a proper machine shop porting isn't cheap maybe in Israel but here it is expensive if you can't do it yourself. See personally if I couldn't SC or TC my car I would pull the heads and the oil pan and CAREFULLY change the crank and pistons, upgrade the fuel injectors and rails upgrade the ignition, possibly change all the valve train components and cams themselves. POrting is nice if you can do it yourself but I've only seen it really effective in a forced induction setting. Decking the heads and or block has some potential problems as listed above with over heating but I wouldn't worry too much about detonation because if you don't change the actual shape of the head there shouldn't be any new hot spots.

[ZfrkS62]

There are other ways to make power other than compression. Fuel is one of the better ways, thats where the injectors come in. RPM is the other way. If you balanced the engine and destroked it, you could spin a couple thousand more RPM.

My ex-boss has a civic that spins 13,000. Just by balancing :wink:

but by deboring/stroking a 327 to a 286, the guys in the shop next to us got a 67 Nova to launch at 12 grand, shift at 11 and redline at 13. and this is a V8 :wink:

so before you go running around to find out who will do the best job for the least amount of cash at shaving off a couple thousanths of metal...i'd look into stroke and bore changes.

[sergei_dekker85]

There are other ways to make power other than compression. Fuel is one of the better ways, thats where the injectors come in. RPM is the other way. If you balanced the engine and destroked it, you could spin a couple thousand more RPM.

My ex-boss has a civic that spins 13,000. Just by balancing :wink:

but by deboring/stroking a 327 to a 286, the guys in the shop next to us got a 67 Nova to launch at 12 grand, shift at 11 and redline at 13. and this is a V8 :wink:

so before you go running around to find out who will do the best job for the least amount of cash at shaving off a couple thousanths of metal...i'd look into stroke and bore changes.

well too bad thats illegal here and that'll fail inspection tests.... :( :(

[sergei_dekker85]

(TCing and SCing is illegal in my country FYI)


that's gotta be the dumbest thing i've heard since finding out norway gives out fines for modded mopeds :?

believe it or not yes...saying that "will compromise the structual integerity of the veh and will compromise on emissions"....wtf well if u'd want to u'd have to go thru alot of paperwork...getting the blueprint of the model of the TC or SC that u're fitting and a confirmation letter from the car manufacturer that this model is safe for fitting into this veh. and will not effect the veh in emission standards and safety...what a pile of CRAP

[sergei_dekker85]

heres the link to my country's yes and nos of mods :http://www.onemotoring.com.sg/publish/onemotoring/en/motoring/information/left/maintain___repair0/modification_guide.html

get this...NOS is not allowed too

[ZfrkS62]

well too bad thats illegal here and that'll fail inspection tests....


what do they do? disassemble the engine and measure everything :?: :!: :shock:


believe it or not yes...saying that "will compromise the structual integerity of the veh and will compromise on emissions"....wtf well if u'd want to u'd have to go thru alot of paperwork...getting the blueprint of the model of the TC or SC that u're fitting and a confirmation letter from the car manufacturer that this model is safe for fitting into this veh. and will not effect the veh in emission standards and safety...what a pile of CRAP


so i take it a twin turbo supra is non existant there? note to self: do not move to singapore :(

[sergei_dekker85]

well too bad thats illegal here and that'll fail inspection tests....


what do they do? disassemble the engine and measure everything :?: :!: :shock:


believe it or not yes...saying that "will compromise the structual integerity of the veh and will compromise on emissions"....wtf well if u'd want to u'd have to go thru alot of paperwork...getting the blueprint of the model of the TC or SC that u're fitting and a confirmation letter from the car manufacturer that this model is safe for fitting into this veh. and will not effect the veh in emission standards and safety...what a pile of CRAP


so i take it a twin turbo supra is non existant there? note to self: do not move to singapore :(

NONONO...what it means that If yr car is Naturally aspirated its illegal to be TCed or SCed....but if a car comes Stock with a TC or a SC then if u wanna change it to a better one its allowed

[lev_p]

NONONO...what it means that If yr car is Naturally aspirated its illegal to be TCed or SCed....but if a car comes Stock with a TC or a SC then if u wanna change it to a better one its allowed

Are you sure that they can see that as well? Over here you usually get away and yearly MOT with a TC or SC, since those assholes that check your car have no idea what it is :lol: And you can always sell them an idea that that huge intercooler pocking out from yuor front bumper is actually an enlarged AC cooling unit :lol:

[lev_p]

Not always the case on some head designs you cannot take very much off of them or you will affect the width of the cylinder and the fact that some have such low clearance heads in order to save room it would be quicker and easier to deck the block. You rarely would have to change the computer for compression ratio changes since there are no sensors for compression ratio last time I checked. And last time I checked if you take your heads to a proper machine shop porting isn't cheap maybe in Israel but here it is expensive if you can't do it yourself. See personally if I couldn't SC or TC my car I would pull the heads and the oil pan and CAREFULLY change the crank and pistons, upgrade the fuel injectors and rails upgrade the ignition, possibly change all the valve train components and cams themselves. POrting is nice if you can do it yourself but I've only seen it really effective in a forced induction setting. Decking the heads and or block has some potential problems as listed above with over heating but I wouldn't worry too much about detonation because if you don't change the actual shape of the head there shouldn't be any new hot spots.

Now, what you describe T-Bird, is actually a lot of work :? BTW, there is no single flow-bench in this country, but there are still a few ppl that learned how to do it properly over the years. Pug engineers where shocked when they heard this :lol:
You are right, there are no sensors for compression ratio (how the hell they can exists?), but still, when you enlarge compression ratio, some physics change inside the cylinder, so it's better to correct that.
For example, M-B has the same engine but with different compression ratios. So for a different compression ratio they fitted a different ECU.

[ZfrkS62]

well too bad thats illegal here and that'll fail inspection tests....


what do they do? disassemble the engine and measure everything :?: :!: :shock:


believe it or not yes...saying that "will compromise the structual integerity of the veh and will compromise on emissions"....wtf well if u'd want to u'd have to go thru alot of paperwork...getting the blueprint of the model of the TC or SC that u're fitting and a confirmation letter from the car manufacturer that this model is safe for fitting into this veh. and will not effect the veh in emission standards and safety...what a pile of CRAP


so i take it a twin turbo supra is non existant there? note to self: do not move to singapore :(

NONONO...what it means that If yr car is Naturally aspirated its illegal to be TCed or SCed....but if a car comes Stock with a TC or a SC then if u wanna change it to a better one its allowed

ok i see. But how would they find out that the engine displacement is different? it might increase the Nox a little due to the heat caused by higher compression. But if you change the cam timing 1 or 2 degrees, it should counter act the temp increase.

[FoxFour]

Another option to maximize the power of the vehicle that you have is a steeper drive axle ratio. Proper gearing can sometimes make a world of difference acceleration-wise. You are not increasing horsepower ot torque, just optimizing the power that you have.

[sergei_dekker85]

Another option to maximize the power of the vehicle that you have is a steeper drive axle ratio. Proper gearing can sometimes make a world of difference acceleration-wise. You are not increasing horsepower ot torque, just optimizing the power that you have.
I'm afraid its impossible cos I'm using an auto transmission as of right now.... :cry: :cry: :cry:

[T-Bird]

Another option to maximize the power of the vehicle that you have is a steeper drive axle ratio. Proper gearing can sometimes make a world of difference acceleration-wise. You are not increasing horsepower ot torque, just optimizing the power that you have.
I'm afraid its impossible cos I'm using an auto transmission as of right now.... :cry: :cry: :cry:

Um actually you can change drivetrain axle ratio in an automatic because that has nothing to do with the tranny itself unless it's a transaxle but it is still doable. you change the gearing in the differential I went from 3.25's to 3.73's and it makes a world of difference I thought about 4.10's but that was a little much for a daily driver.
And I don't understand how balancing an engine so that it will actually be stronger and last longer (while making it be able to rev the living hell out of it) can be illegal in your country since they would have to actually take the engine apart. I say use all lightweight internals and stroke the engine. Also since you have an Auto look at possibly changing out your torque converter to get way better delivery of torque and possibly better Torque multiplication.

[ZfrkS62]

alot of those laws don't sound enforceable sergei. i highly doubt they will tear down your engine to check if it's been bored and/or stroked. and a balanced engine is damn near impossible to check for.

[T-Bird]

see this is why I love Illinois, the only test they do is Emissions and that isn't every year so you can have a fucking turbo the size of a 747 engine in there and they can't say shit if it passes emissions. And for me to pass emissions I went to school hooked up the Genesis and tweaked a few things (after saving the original settings) so that it would have lower emissions, some things that weren't really allowed also such as turning off every warning light so if they came on they wouldn't see it. Then I went to the gas station and put in some nice ol' racing fuel 130 Octane and passed emissions with flying colors.

[ZfrkS62]

see this is why I love Illinois, the only test they do is Emissions and that isn't every year so you can have a fucking turbo the size of a 747 engine in there and they can't say shit if it passes emissions. And for me to pass emissions I went to school hooked up the Genesis and tweaked a few things (after saving the original settings) so that it would have lower emissions, some things that weren't really allowed also such as turning off every warning light so if they came on they wouldn't see it. Then I went to the gas station and put in some nice ol' racing fuel 130 Octane and passed emissions with flying colors.

:usa we may not get the best cars, but at least we can do whatever the hell we want to them :D

[T-Bird]

damn right if the engine isn't big enough get a bigger one if that isn't enough slap on a big ass Blower or Twin Turbo setup if still not enough throw in a mild 350 shot of Nitrous, then slap on a racing tranny then 4.10's in the rear gut the interior install some plexi glass windows and there you have it. And if the car is an older muscle car then you can do it without thinking about emissions even.

[sergei_dekker85]

alot of those laws don't sound enforceable sergei. i highly doubt they will tear down your engine to check if it's been bored and/or stroked. and a balanced engine is damn near impossible to check for.

well Engine balancing is definitely allowed but changing the Bore and stroke is not allowed....heard that when u send yr car 4 inspection they can tell if its been bored by the sound... :shock: :shock:

[ZfrkS62]

alot of those laws don't sound enforceable sergei. i highly doubt they will tear down your engine to check if it's been bored and/or stroked. and a balanced engine is damn near impossible to check for.

well Engine balancing is definitely allowed but changing the Bore and stroke is not allowed....heard that when u send yr car 4 inspection they can tell if its been bored by the sound... :shock: :shock:

not on a 4 banger! V8 then MAYBE. upping the compression is much more audible than boring/stroking. it sound ALOT tighter, more forceful.

on a 350 that's been taken out to a 383 (punched .030 over) you might get a slight lope to it, but you can compensate for that with fuel. Just run it slightly lean and bingo bango it sounds more like a 350 again :D if it sounds like its idling too low, richen the mixture to bring the idle up.

adding a camshaft you can definetly hear at idle, but on an overhead cam engine, it's not that difficult to swap the cams out for inspection shouldn't take much more than 2 hours.

hell, worst comes to worst you could always buy a second engine, build that one up and just take it out for the inspection. They would never know you have two engines for the car. FWD cars are simple to yank the motors out of. i've done civic's in about an hour and a half, out in and running. two of us did it in 45 minutes once. (this is when i was working in Phoenix). Baisicaly, there are so many ways around that crap that they're talking about it's not even funny. And if they want to try and match numbers on the new engine to the car, just tell them the original one blew up. not much they can do there :D :wink:

[sergei_dekker85]

alot of those laws don't sound enforceable sergei. i highly doubt they will tear down your engine to check if it's been bored and/or stroked. and a balanced engine is damn near impossible to check for.

well Engine balancing is definitely allowed but changing the Bore and stroke is not allowed....heard that when u send yr car 4 inspection they can tell if its been bored by the sound... :shock: :shock:

not on a 4 banger! V8 then MAYBE. upping the compression is much more audible than boring/stroking. it sound ALOT tighter, more forceful.

on a 350 that's been taken out to a 383 (punched .030 over) you might get a slight lope to it, but you can compensate for that with fuel. Just run it slightly lean and bingo bango it sounds more like a 350 again :D if it sounds like its idling too low, richen the mixture to bring the idle up.

adding a camshaft you can definetly hear at idle, but on an overhead cam engine, it's not that difficult to swap the cams out for inspection shouldn't take much more than 2 hours.

hell, worst comes to worst you could always buy a second engine, build that one up and just take it out for the inspection. They would never know you have two engines for the car. FWD cars are simple to yank the motors out of. i've done civic's in about an hour and a half, out in and running. two of us did it in 45 minutes once. (this is when i was working in Phoenix). Baisicaly, there are so many ways around that crap that they're talking about it's not even funny. And if they want to try and match numbers on the new engine to the car, just tell them the original one blew up. not much they can do there :D :wink:

Nope....u need 2 have paperwork that u swapped the engine and My car isn't Fwd...its 4WD...

[ZfrkS62]

Nope....u need 2 have paperwork that u swapped the engine and My car isn't Fwd...its 4WD...


even if you buy and install the engine yourself? damn dude, i think it's time to move :? I'd go bonkers if i couldn't fuck with my car.

Do you have to get the letter from a shop? or the engine supplier?

and 4wd isn't that much harder to do. just disconnect the drive shaft to the rear diff and drop the engine/trans assembley out the bottom :wink:

[sergei_dekker85]

oh course this place sucks.....we only have ONE go-kart track and its not even international standards...the current govt. discourages that...and get this...the traffic police have QUOTAS for traffic offences every month so u'll get caught even for making the slightest mistakes sometimes....wtf..How i wished i was back here in the 70s where my country had a F1 circuit..2 bad its now closed and only part of the track remains and thats where street racers gather... :roll:

[ZfrkS62]

oh course this place sucks.....we only have ONE go-kart track and its not even international standards...the current govt. discourages that...and get this...the traffic police have QUOTAS for traffic offences every month so u'll get caught even for making the slightest mistakes sometimes....wtf..How i wished i was back here in the 70s where my country had a F1 circuit..2 bad its now closed and only part of the track remains and thats where street racers gather... :roll:

dude, i feel for ya :(

cops here have quotas for tickets too. at the end of the month the speed tropas start showing up :wink: :wink: they'll write you a ticket for stuff sometimes even when they know it will get dropped

[T-Bird]

alot of those laws don't sound enforceable sergei. i highly doubt they will tear down your engine to check if it's been bored and/or stroked. and a balanced engine is damn near impossible to check for.

well Engine balancing is definitely allowed but changing the Bore and stroke is not allowed....heard that when u send yr car 4 inspection they can tell if its been bored by the sound... :shock: :shock:

not on a 4 banger! V8 then MAYBE. upping the compression is much more audible than boring/stroking. it sound ALOT tighter, more forceful.

on a 350 that's been taken out to a 383 (punched .030 over) you might get a slight lope to it, but you can compensate for that with fuel. Just run it slightly lean and bingo bango it sounds more like a 350 again :D if it sounds like its idling too low, richen the mixture to bring the idle up.

adding a camshaft you can definetly hear at idle, but on an overhead cam engine, it's not that difficult to swap the cams out for inspection shouldn't take much more than 2 hours.

hell, worst comes to worst you could always buy a second engine, build that one up and just take it out for the inspection. They would never know you have two engines for the car. FWD cars are simple to yank the motors out of. i've done civic's in about an hour and a half, out in and running. two of us did it in 45 minutes once. (this is when i was working in Phoenix). Baisicaly, there are so many ways around that crap that they're talking about it's not even funny. And if they want to try and match numbers on the new engine to the car, just tell them the original one blew up. not much they can do there :D :wink:

Nope....u need 2 have paperwork that u swapped the engine and My car isn't Fwd...its 4WD...

OK so you build up the new engine and use the original for inspections then they don't need any paperwork because to them you never swapped any motor. And zrfks62 is right it is easier to hear different compression ratios then it is to hear boring and stroking when it comes to smaller engines especially.

[basy]

Did you think that is better buying a car with turbo? I think it is more efficient if you can tune much easier a turbo? I think this is the best solution for your country.

[ZfrkS62]

dude, this is called a dead topic. Reviving dead topics is generally frowned upon.

And no, it is NOT easier to tune a turbo engine. It's actually much harder because you need to know what is going on in the combustion chamber. If the mixture leans out at any point, or if temps inside the chamber get to hot, you are going to need to replace your pistons because you just burned a hole in the tops of all of them.

[ZfrkS62]

dude, this is called a dead topic. Reviving dead topics is generally frowned upon.

And no, it is NOT easier to tune a turbo engine. It's actually much harder because you need to know what is going on in the combustion chamber. If the mixture leans out at any point, or if temps inside the chamber get to hot, you are going to need to replace your pistons because you just burned a hole in the tops of all of them.


Thx Z guy, you saved me from saying it.....

I wonder where these people come from who thinks tuning a turbo car are so much easier than anything else......fast and the furious anyone....Im surprised he didnt come up with a line like "put some NOOOOS on it and blow em away dawg".... :roll:

:lol:

It's just that misconception that you and i talked about awhile back. THe misnomer of instant power from FI.

Slowly, the ignorant become educated :wink: well...some of them :lol: