What FP do are cars usually run at.I'm running mid 40's right now.Should I go up or down with it.What kind of change does the FP make at WOT.

 

If you lower the fuel pressure with an AFPR, you will lean out the A/F ratio. But the PCM sees that during closed loop operation (low/part load) and alters the pulse widths to make up for the missing fuel, and develops long term fuel corrections (BLM's) to keep that fuel supplied. When you go WOT, since the PCM was adding fuel in closed loop, it will use the BLM's from Cell 15, and put the A/F ratio at WOT right back where it was before you changed the fuel pressure.

Leaning out the LT1 can net you 15HP, because the 11.7:1 A/F ratio the PCM typically uses at WOT is too rich. But you need to correct it with PCM programming (PE tables) or with something like the MAF-translator.

If you are pushing your injectors to the limit (400HP for the 24# stockers) increasing the fuel pressure can lower the duty cycle and give you a little cushion before you max them out.

 

So what FP would be considerd lean in an LT1.

 

The stock fuel pressure (43.5psi +/-2.5psi with the vacuum line off) yields the 24.9#/HR injector flow constant programmed in the PCM. So every calculation the PCM makes assumes you have 43.5psi. If you alter the pressure, the PCM can't tell directly, but it sees the mixture richen or lean in response to the fuel pressure change, then sets the BLM's to correct the calcualtion.

At part load, the PCM runs in closed loop, and tries to maintain an A/F ratio of 14.7:1. At WOT, it calculates a "target" A/F based on a few variables, but in general will target 11.7:1. You would probably get better results in the range of 12.8-13.2:1 (some people have got best results at 13.5:1).

But, unless you keep it in open loop, lowering the fuel pressure won't lean out the A/F at WOT. If you raise the pressure, it will richen the mixture, but its already too rich, so that would serve no purpose.

 

How can I tell what A//F ratio is? I look in Freescan and PCMComm, but don't find it.

So are you saying I need to see BLM at WOT under load, then adjust it?

From what I can find, the BLM should be at 128. Its there without load in the driveway at 2000-3000 RPM. I'm going to try to get to a drag strip to test it today under load.

How do I adjust the PE if I see BLM less than or greater than 128?

thanks for any info

BobC