Here's a thought, and it would take some logic to implement and tune correctly, but why not spray E85? It's compatible with high-pressure EFI pumps and injectors, and the ethanol provides an evaporative cooling effect.
Disclaimer: I have consumed a few alcoholic beverages this evening.
Because all you just did was implement a second EFI set-up.
I'll try to keep it short by letting you guys do your own verification of some of my numbers ...
Stoichiometric for gasoline is 14.7:1 .
The best power is around 12:1
Most turbo application run up to 9:1
Why the differences? Cooling. Anything above stoichiometric is used to cool the intake charge. So what I did was replace the cooling gasoline and replaced it with cooling water. Water and not a mix of 50/50 alcohol because alcohol is a fuel and if I wanted more fuel, I add more fuel via the EFI. I was running a fully programmable EMS that was also controlling the water injection solenoids based on RPM and boost. The interesting part here is the 12:1 number. It seems to be universal - in boost or in vacuum. It's above stoich, so I imagine that it's that high because there isn't 100% homogenization and evaporation of the charge and you are not burning the charge completely. The fact that engines soot and soot is a result of incomplete burning is proof in my mind of this theory.
So, what I did was calculate the latent heat of evaporation of gasoline of the extra fuel being injected (9:1 vs. 12:1). I then figured out how much water I needed to replace that at certain boost levels and RPM. You can basically ignore the temperature changes of your water injection as 95% of your cooling is via evaporation (people who throw ice in their water injection tanks amuse me). So with water injection, you can run a more powerful air-fuel ratio safely. There are also calculations that need to happen for air volume, post turbo temperature, pre- and post- intercooler temperatures and actual pressures throughout the intake tract.
OK, so we know how much to inject - The where to inject it was via experimentation. I started post IC then went to pre-IC. My thought process was that the water would have more time to evaporate and cool the charge. I was right. I believe that I had close to 100% evaporation by the time the charge got to the butterfly. My temps were down. A sidenote here is that you will reduce the "efficiency" of your intercooler. They work by taking heat out of the system based on the differences in temperature of the intake and ambient air. So if you reduce the intake charge temp before the IC, you are not going to get as large a temperature difference and therefore a lower efficiency. However, your IC will not heatsoak as quickly. Also, your turbo will spin different. This is because you are reducing the pressure on the pressure side of the turbo via cooling the charge there before it hits the actual physical obstruction of the intercooler. So instead of pressing against 20psi of air, you would be pressing against 17psi for example. This is important since your turbo will spin faster to create the same pressure in the plenum. So depending on where you are on your efficiency islands, this could be bad.
So why didn't that work better?
I did end up going back to the post IC and as close to the butterfly as I could. The highlights are: The intake charge temp ended up being a few degrees higher. But I was able to inject more water before losing power/getting a stumble. Overall I was able to get more power this way. What I think was happening was that I was getting droplets of water into the cylinders. This was creating a steam engine effect. IE the droplets expanded to 1000x their size upon ignition of the charge and that created additional pressure and upping my "brake mean effective pressure." So I had a higher pressure at a lower temperature in the cylinder - exactly what you are looking for in an engine. Again, I can't prove anything but I think the droplets of water also helped homogenize the intake fuel charge whereas water injection pre-IC created a higher density air-charge that didn't disperse the fuel as well.
Anyway, that's my experience.
--Rob Leone Schumacher Taxi Service We won the IOE
at Southern Discomfort.We got screwed at The Real Hoopties of New Jersey
and we took cars down with us.We got the curse at Capitol Offense
but they wouldn't let us destroy the car.