Why do/can WRX's run so rich?

[gobs3z]

I was coming home a few nights ago on the highway, and an STi passes me going about 90-100mph and then hits some traffic. I catch up to it just to check it since it was loud as $hit. Well he was give it some boost and let off the gas and a 2 foot flame would blast out of its tailpipe. I know that WRX's run rich from the factory running 400+ cc injectors (thats a substantial modification for my car). Why do they run so rich from the factory, if those injectors were in my car i'de be pushing 300hp and those injectors are in the Impreza not the STi. Does it have to do with the engine being a boxer, then does that mean Porsches run that rich as well?

[sentra_dude]

Most likely its a safety feature, especially since the car is turbo-charged. Running lean makes the engine run hotter and gives you a better chance of causing engine damage, so they are probably just playing it safe by staying on the rich side, which helps engine cooling and reduces the chance of not getting enough fuel in the combustion chamber (on the tuned car).

I'd say it has very little, if anything, to do with the engine configuration. It's a little surprising that they would run the car that rich from the factory, since that would hurt fuel consumption a bit, but I guess they are more worried about the engine staying cool.

[espen]

They do not run particularly rich. If it blew flame then the cats are all gone, meaning there are probably more mods. Catless and given a good whipping, any Impreza running an athmospheric dump valve will shoot flames.

I've seen WRX'es that run just fine but i max the injectors at a modest 1.05 bar (this particular one made 265 hp). Likewise, the injectors on a stock STI will only support a little over 300hp (if you run them properly) - negating the possibility of running it overly rich at rpm. After all, its the mapping that dictate AF - not injector size

[nthfinity]

all gasoline engines run rich... often to cool the heads, and in turbocharged aplications, it can be an anti-lag system... although, im not sure if that is how, or if its an injector for the turbo.

its widely known that many STi components are on the 'tame' side of thier tuned potential.

[dingo]

Are you sure he wasn't just running anti-lag? There are a few guys in the WRX club here that have it, and when going through the tunnel (best place to see/hear it) they shoot flames when getting off the throttle....

[gobs3z]

I could be possible he was running anti-lag. It just seems like for the injector size they run they should be pumping out more horsepower. The only other car that runs even richer than that are RX-7's, 700cc injectors. But the RX-7 is a rare case and a 12mpg car. Thanks for the info!

[espen]

Injector size isnt like carb jets, you know. Injector size has nothing to do with power or fuel comsumption as long as they are big enough and the ecu is mapped right. It's not uncommon to run pink STI (565ccm) injectors on WRX engines and still consume exactly the same amount of fuel. Just adds capacity so you don't have to run them over 85% duty.

And you are aware that RX7s don't have four injectors like on a four cylinder engine, right? 700ccm is no more than adequate

[Wutputt]

I would also doubt a 100% standard runs rich. Though, the tuned ones, that's another story

Originally Posted by sentra_dude It's a little surprising that they would run the car that rich from the factory, since that would hurt fuel consumption a bit

... and would also hurt the catalytic converter after a while.

Originally Posted by nthfinity all gasoline engines run rich...

All standard gasoline engines with a catalytic converter (i.e. almost every current gasoline engine) runs stoechiometric and allows only a slight deviation from this theoretical air/fuel mixture. The exceptions are some engines with direct injection; under certain conditions they are running on a stratified mixture, and some small scale performance oriented engines.


The fact you see flames coming out of the exhaust of a WRX, has most often to do with an open exhaust and a vent-to-atmosphere BOV which results in unburned fuel escaping the cylinder and getting burned in the hot exhaust. If the flames are really big, an anti-lag system may be the cause of it, but certain owners also put injectors in the exhaust just to show off...



EDIT: sorry Espen, I overlooked your post. You already said it all

[coombsie66]

The actual fuel that the injector passes is also entirely dependant on the fuel rail opperating pressure, injectors can cope with anything from 3-5 bar, which substancially alters your duty cycle %'s.

[gobs3z]

I guess my only issue in questioning WRX's is if you were to put a WRX next to my car with the same modifications. Turboback exhaust (no muffler), intake, chip, and DV, and revved them both up next to each other the WRX would shoot flames while my car would pop a lot but no flames. (I'm not saying i want flames shooting out of my car, i was just curious why WRX's are flame throwers) I have actually never seen a 1.8T dispense flames before. Even fairly tuned 1.8T's don't seem too. What it seems to me is that since the WRX needed 3 cats to pass emissions, instead of detuning the engine they just gave it a very restrictive exhaust so once you put on an aftermarket exhaust it just lets out the full potential of the stock engine which is actually highly tuned from the factory (compared to most cars).

[espen]

Golf 1.8T is no match for a BPU Impreza. Fit your 1.8T with an open dump, up the boost and remove your cats and it will spit flames - seen it many times at track meets. it's a mapping issue, not an engine issue.

[gobs3z]

I've done that and it'll make very loud backfires but deffinately no flame.

[Tyrone]

I love the sound of the WRX however the car looks cheap inside and out. The dashboard is so ugly and so japanesio. The thought and sight of bogans and nerds driving the WRX has put me off even thinking about it for good.