jorj7

If I read this right, when I moved my fuel filter from in front of the fuel rails (right before the Y) to the back of the car, the distance that the pressure wave travelled was greatly increased. That could be why I don't have the oscillating fuel pressure any more. Interesting data point.

George
90 S4 Grand Prix White (Murf #5)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com

jorj7

Talked to Bill today about this idea, and he thinks it's not worth the hassle, we're already too rich at speed during the race. Why boost the pressure if it'll just make it richer (and heat the fuel more). So we'll skip this for now. If we get to a point where we're running lean, while running over 80% duty cycle, then we'll look a delivering more fuel.

At this point, we're trying to figure out how to get more air into the cylinders..., and fix the crank case breathers, and keep all the fluids cool.

Thanks,
George
90 S4 Grand Prix White (Murf #5)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com

ptuomov

I don't think I was specifically suggesting that you should increase the base pressure. If you go with two stock regulators, you should have 47 psi at idle, 55 psi at full throttle but before boost starts building, and 55 psi plus boost above that. I guess that would work out to about 70 psi with 15 psi boost. At high rpms and full load, that's more than you currently have.

I personally think it's easier to get the AFR right in all conditions, if the fuel rail pressure compensates for the manifold absolute pressure. I don't have a strong opinion on the base pressure, but I do think that one needs to get the fuel pressure regulator to compensate manifold pressure 1 for 1 to be able to take a full advantage of the benefits provided by hot-wire MAF. My preference is to do it that way.

Another thing that I don't like about aluminum "billet" fuel pressure regulators is that I suspect they are inconsistent because thermal expansion of aluminum is large. Another personal preference.

GregBBRD

I too would think that tuning with a regulator/regulators that allowed the pressure to rise would make tuning much easier.

However, since you have already tuned the car without this and you have reasonable fuel air mixtures, any change might be an exercise in futility. The change would also "expose" you (and Bill) to a whole bunch more tuning time.

I'd say that as long as you know that you are not running out of fuel over a long run and the pressures are fairly stable, to forget it.

Carl Fausett

Yes, that is correct. You increased the distance between the reflective points, increasing the system size, and negating the dampener and the pressure-wave knock at the same time.