Tuning: EGTs after adding water injection
 

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

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.

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?

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

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.

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...

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.

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.

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