Tuning: EGTs after adding water injection

[Andrew]

I have recently installed a WI system and am wondering what kinds of effects I should be seeing as far as exhaust temperatures.

This is a "stage 4" WRX, using 91 octane fuel and injecting pure water. Currently, water delivery is ~15% of fuel volume at maximum flow (measured), and is metered by the Aquamist FiA2. My tune is basically a 91 octane-only tune with the WI added on top of that.

Under boost, my EGTs peak close to 1500 F. As I understand it, I should be seeing significantly lower EGTs with water than without. But this is not what I am observing.

So, I have a couple of questions for those of you who have experience tuning WI successfully.

1. What EGTs should one see when adding water to a gasoline-only tune?

2. How much water (or water/alcohol mix) are you using? Details on how you calculated and/or measured this number would be great.

Andrew

[AKWRX]

Adding water, or a water/alcohol mix when tuned for pump gas may show little, or no, reduction in EGT. The reduction of EGT (near WOT) is mostly due to the much more agressive ignition advance allowed by the increased knock threshold when injecting. For example, for a similar UTEC controlled TXS Stage 4+, at up to 23psi boost, ignition advance in the range of 30-34 degrees dropped the EGT at WOT from 1550F down to no more than 1460F. That's knock free on 92 octane pump gas, injecting a rising rate of 85% methanol and 15% water mix.

[Andrew]

AKWRX, thanks for your reply. Can I ask what the ratio of alcohol/water injection to fuel is on the car that you mentioned?

I'm not really sure where to proceed from this point. My concern is that my EGTs approach 1600 F near redline with an AFR of 11.1-ish (on wideband), with water injection. I would like to lean the mixture out but my EGTs are high enough that I don't think I have any room to move. Can you suggest a method of safely moving to a leaner mixture?

[cmetzner]

The reduction of EGT (near WOT) is mostly due to the much more agressive ignition advance allowed by the increased knock threshold when injecting.

AKWRX

How much more timing would you expect to add because of WI?

I have the 2d system to intercool for an M62 sc on my miata running on 91 octane her in Calif. The boost is only 6.5psi.

I have a timing control box/computer that removes the stock timing advance under boost. I remove 20% of the mapped timing retard (4 clicks of the timing knob) when I run WI.

I have asked this question a number of different places and do not get an answer. Just wondered if you have any insight?

Thanks -- Chuck

[AKWRX]

AKWRX, thanks for your reply. Can I ask what the ratio of alcohol/water injection to fuel is on the car that you mentioned?

I'm not really sure where to proceed from this point. My concern is that my EGTs approach 1600 F near redline with an AFR of 11.1-ish (on wideband), with water injection. I would like to lean the mixture out but my EGTs are high enough that I don't think I have any room to move. Can you suggest a method of safely moving to a leaner mixture?

You asked the $64,000 question. Honestly don't know exactly what the ratio of injected alcohol/water to fuel is. My system starts injecting at about 6 psi boost, and ramps up to full injection line pressure (100 psi) at 16 psi boost. So, it varies, but the amount of injection is still relatively small.

Since you are running rich anyhow, it may be best to first focus on reducing your EGT, for safety purposes if nothing else. That can be best done by increasing ignition advance until some knock counts show up, and then backing off a bit. At that point, you may be able to start leaning out the fuel map for more power as long as everything remains knock free. My A/F near WOT is somewhere in the range of 11.8 to 12.5, so I think there is still room to pull some more fuel out. Scary stuff when the boost is bumping the UTEC default cut of 20.5psi.

[AKWRX]

AKWRX
How much more timing would you expect to add because of WI?

I have asked this question a number of different places and do not get an answer. Just wondered if you have any insight?

Thanks -- Chuck

Sorry, don't have any hard numbers for you either. No experience with a Miata (but it may be my next project car). See my post above...

[Andrew]

Hmm... Well I tried advancing my ignition curve 1-2 degrees in places, but I'm getting a little knock. EGTs have not reduced and I think I'll have to go back to my original ignition curve.

Should I try adding some methanol to the water?

[AKWRX]

Hmm... Well I tried advancing my ignition curve 1-2 degrees in places, but I'm getting a little knock. EGTs have not reduced and I think I'll have to go back to my original ignition curve.

Should I try adding some methanol to the water?

It is important to remain knock free. You may have all the ignition advance that the current setup will presently handle. Don't know if adding some methanol will help. It most likely is a "quantity", and "when" injection issue. There are others on these boards that have more experience with your WI hardware, and should have better input...maybe they will chime in.

[robbilau]

I know that Shiv Pathak has a dubious opinion of WI on WRXs based on his experience tuning them. I don't know if this is due to a lack of expertise or if it's a symptom of the WRX form some reason.

[cmetzner]

Doesn't Aquamist claim that many/most rally cars use water injection? That would include WRX's

[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]

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]

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

[Andrew]

Okay, here are some of the relevant parameters.

Engine: Stock WRX 2.0L
Turbo: SR30
Intercooler: Stock
Water injection point: ~5psi

Hotrod, your comment about the sweet spot got met thinking, so I went back and checked the compressor map that I have. Sure enough, at higher rpms, the turbo is running at a lower efficiency, so I lowered boost from ~17.5 to 16psi from 5500 and up. My max boost is about 18psi in the 4000-5000 rpm range.

I just made the change this morning, so I'll drive it a little and see how things have changed. I'll also post a log.

[Giles Gilbert]

Any update on this?

[SaabTuner]

This thread brings an interesting question to mind.

Why don't more upgrade packages include items to raise the effective EGT limit?

I constantly see upgraded engines designed to "flow more", or to be "stronger" ... but EGT is one of the hugest limitations to engine performance. Why not and engine that can "take higher temperatures"?

There are probably one or two upgraded engine packages sporting Inconel or Nimonic exhaust valves. (Or maybe Hastalloy, or Waspalloy, those are awesome.) But you just don't see that sort of thing happening much. The only changes I usually see are Inconel turbines, Inconel wastegate valves, and occasionally ceramic coated exhaust valves. Usually though, people market ceramic coatings as reducing under-hood temps. Oh well.

Sorry for the OT. I just see so many people fighting this "wall" so to speak. 1600 is NOT a finite limit. That barrier can be moved, and it might be cheaper to move it than to lower your EGT.

Adrian~