Ah. Well I was talking about lowering the fuel pressure, not increasing it.

 

Jake, when you lower the pressure like that to squeeze more out of the pumps, do you change the IFR in the tune? I've always wondered if that will fix fueling or do you have to retune the MAF/VE?

 

The only reason to lower the fuel pressure would be to get the pumps into a range where they don't drop off at the high end (say 58 base + 20 boost, 78 lbs). The Walbros drop off a lot over 75 lbs because of the relief valve. Disabling the valves makes them not drop off as much so you can still run higher pressures.

 

Reducing the IFR for the new fuel pressure seems to take care of everything as long as your injector data is good. I always check VE to make sure everything is good though.

The pumps flow less at higher pressures, but not because of that valve. Liquid is relatively incompressible, so the more pressure you run the less volume the pumps will actually move. You may have issues trying to squeeze 700hp out of 255s at 58psi base on e85. Just a little forewarning. Aromic did a writeup on it if you'd like to reference that.

 

The pressure mod is not a cure all, the Walbros still lose a lot of volume at higher pressures. But not allowing the pressure relief valve to open at 75 psi helps a lot.

Look at the following picture, notice how the slope changes drastically @ 75psi. A modded pump will not fall off as fast.

http://autoperformanceengineering.com/pics/255lph.jpg

So far I've got enough fuel, we will see how far it can take me. I run the GTO around 45lbs base so 65lbs under boost and it has plenty of fuel for over 1000hp at the flywheel.

I'll try to get some videos this week.