[MartinLe]

Originally Posted by Joshinator99

Higher pressure equals less flow through the HPFP (or any pump for that matter). So, it depends on your fueling needs. You’ll have to datalog and adjust as needed. If your IPW is getting much over 6.0ms, then try tweaking up the HPFP pressure but you’ll have to keep a close eye on it…when rail drops off it can be fast. LPE recommends 2175 because that is max flow, but you can run higher pressure if needed.

Originally Posted by KingLT1

I have run them both at 2900psi, but it's right on the edge of misfire and a stock low side pump with JMS won't keep up. LPE has never said their pump will support 2900psi to me and I have spoken with a couple guys there (I live 30 minutes away). Perhaps they been reading these forums and have read my posts stating it will Lol. They told me it would pop the O ring but it never has. I have had FIC +30 hold 2900psi and some misfire. The XDI +30 will hold 2900 psi but the +65 are 2600 max.


On a SS LT1 P1x pushing 10 psi peak I found 2500 psi worked best and provided the most fuel headroom with this fuel system. It was stable to E70 @ .82 lambda. This setup hits much softer so it doesn't tax the system on the hit.

On a FBO ZL1 with Kong port and 2.17, I needed the high side set low as possible because it wants to bleed the rails on the hit. I actually have to start with a leaner AFR(.87) and blend down .84. It holds E62 fine @ 14psi.

On my SS LT1 Whipple 2.9 setup I started at 2900psi and the high or low side wouldn't keep up. Dropped to 2500 psi, low side was fine high side was still dropping some. Went down to 2175 and both hold steady on E60 @ 10 psi .82 lambda.

Injectors are in the 5.5-5.7ms range on all the above. Commanding more pressure attempts to lower Injector ms down to 5.0-5.2 but soon as the high side starts dropping, they open up to 5.8-5.9

So, it all comes down to finding what works best on a particular combo. A stronger low side would likely help hold higher pressure.

OK, in a perfect world, we have 75# low side and 2900# at the rail and IPW's in the mid 5's. Of the three numbers, the IPW's are the most important in keeping the motor in one piece. Now we have some fluctuation in the fuel pressure, but the IPW's stay in the happy zone. During a run, the low side hangs in there at 70#+ and IPW's are in the low 5's. At the shift into second at 7K, in that little window of rpm drop at the disengagement of the clutch, the rail pressure drops to 2000# (low side 70#) and the IPW's raise to 5.8 - 5.9 for a split second, and then rail goes up to 2800# and IPW's back to mid 5's. The motor is happy. This is my understanding.

When I installed the blower/cam package, I was discouraged from the LPE BB pump because it ran at 2175#. "We want to have the 2900# at the rail at all times." You are running a steady 2175# at the rail and the IPW's are in the 5's. How can that be argued as anything less than safe and acceptable? Some tuners will argue the 2175#. But the IPW's are in the happy zone.

As Josh stated, the higher the pressure the lower the volume. The LPE pump will run under some conditions at 2900#, but it is designed for 2175#. Why wouldn't the OEM pump push more fuel at a lower PSI?

I apologize if this is a little derail of the OP's intent, but it is about pressures.