Tuning: EGTs after adding water injection

[robbilau]

That's true. But I have to wonder how much a street WRX has in common with a rally car, though, let alone a WRC car. And this is also just one tuner - a well known one, but just one nonetheless. I was surprised to hear his low opinion myself.

[Richard L]

Andrew,

Not sure if I am correct in saying about your EGT reading is due to a combination of water and rich air/fuel mixture.

Rich mixture tends to slow down burn speed more than water. A retarded burnt will produce high EGT. Water will take some heat away but will also slowdown the burnt further so the cooling effect could cancel each other out.

Try leaning your fuel first and injecting water and see what the effect is.

[Andrew]

Richard,

Your statement is very interesting. You seem to be suggesting that by leaning out my mixture, it will burn faster. By speeding up the burn rate, a retarded ignition curve becomes closer to an optimal curve. Which results in a cooler EGT.

So in this case, leaner mixtures=lower egt? Counterintuitive, but it makes sense....

I'll give it a shot.

[mx5]

Originally Posted by Andrew

Richard,

Your statement is very interesting. You seem to be suggesting that by leaning out my mixture, it will burn faster. By speeding up the burn rate, a retarded ignition curve becomes closer to an optimal curve. Which results in a cooler EGT.

So in this case, leaner mixtures=lower egt? Counterintuitive, but it makes sense....

I'll give it a shot.

In general the right mixture = lower egt. Too rich or too lean can both lead to high egt

[SaabTuner]

I like WRX's along with most turbo cars, but I kind of chuckle at the 1600 degree EGT limit ... most of the Saab tuners out there tune for a "conservative" 1700 for a street car. Suprisingly I've not heard of many turbo meltdowns. I believe Brad from KC Saab has seen some immensely high EGT's for his Viggen, which like mine has Nimonic exhaust valves standard.

The Saabs almost all also have oil squirters for the pistons to keep them cool, forged pistons, and the Viggens, Aeros, and all the newer 9-5 4 cyllinders have Nimonic alloy exhaust valves. Trick stuff! If only every turbo engine came that way from the factory ... :roll:

Adrian~

[Charged Performance]

The WRX has a few things against it - cast pistons, open decks, etc. Though the EGTs may be able to be a bit higher with water injection controlling the flame front even with these shortcomings - there really is no reason to push it. The pressure and torque being generated with 1600 EGTs while using water injection is quite a bit and the cylinders have enough issues with ovalling without increasing the cylinder pressures further.

It will be interesting to see as people start pushing the STi's with their cast (but better) pistons, treated valves and semi-closed decks whether the EGTs and cylinder pressures can be increased. Though some are spinning bearings (probably oil starvation) and cracking ring lands already on the flat-4 2.5's.

[max legroom]

Originally Posted by SaabTuner

I like WRX's along with most turbo cars, but I kind of chuckle at the 1600 degree EGT limit ... most of the Saab tuners out there tune for a "conservative" 1700 for a street car. Suprisingly I've not heard of many turbo meltdowns...Adrian~

The Rex has a "pre-cat" before the turbo. That's the main reason you need to keep EGTs down, or you can end up with abrasive ceramic chunks in the turbine blades. If you replace the up-pipe with a catless one you have more leeway with temperatures. It's illegal to replace it, of course. My guess is, Saab hasn't introduced that sort of self-destructive idiocy into their engines yet. Oh, sorry, it's not idiocy, it's just 20 more seconds of cat exhaust scrubbing before the main cat heats up enough to work efficiently. I suppose if you live in Banff (no offense to the inhabitants of that exquisite land, it's just in general pretty cold...) or tend to drive 30 seconds to the corner store and back this is a good idea. For everybody else it's just a reliability issue that sooner or later needs to be addressed. Aargh.

[Richard L]

Andrew,

Have to managed to control your EGT by altering your a/f ratio?
Just a matter of interest, what afr are you running?

[Andrew]

Richard,

No, I haven't gotten the egts controlled yet. But to be honest, I haven't had much time to devote to tuning lately.

I'm currently running 12.x with WI on my wideband, which is calibrated for gasoline. EGTs are actually poking a little over 1600F near redline now. I'm a little frustrated beacause I can't seem to find the right combination of parameters to make everything come together.

Does anybody have any suggestions?

[hotrod]

It might be helpful if you could give us a bit more information on the engine.

How much boost are you running, confirm which turbo, and intercooler your using, and where your injection point is?

The suggestion I was going to throw out was that you may be running too much boost, and that will not let you get to the sweet spot. Try backing off the boost a couple psi, that should move your knock point and that may allow you to get your ignition timing in a good place.

If you have logging ability it might be useful to some of the folks if you could post your logs. Maybe someone will notice something that will help figure it out.

You may also be running too much boost too early. Most knock prone rpm's should be the mid range rpms. You may also want to try turning on the spray just a bit earlier. If your turbo comes into boost very quickly you may get to high manifold pressures before the spray can really get primed and at full flow. Better to start the spray a bit early and then move up the trigger point slowly. 8 - 10 psi seems to be a common starting point for a lot of engines.

Personally 1500 max EGT is not a big deal in my book, NA engines tuned for max power will frequently run 1460 or so. I'd be a lot more concerned about getting rid of the knock than I would lowering an already moderate peak EGT number. Brief trips up to 1600 -1650 should not be a problem so a peak of 1500 is pretty conservative. Even in one of Subaru's tech pages they mention that the valves are engineered to operate in the neighborhood of 1600 degrees.

http://www.subaru-global.com/about/parts/11.html

Just shooting in the dark here, but hope that helps?

Larry