Quote:
Originally Posted by MartinLe
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.
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Alot of tuners don't understand the LPE pump. LPE pump is a modified LT1 pump designed to run @ LT1 pressure which is 2175psi. It flows 10% more @ 2175 vs the LT4 @ 2900psi. I assume LPE chose to use the LT1 pump as the foundation to make a higher volume pump because the LT4 pump is limited on the size of cam lobe to drive it. The LT4 can only run up to a 38% fuel lobe. The LPE can handle a 43% lobe. So, the 10 % flow increase on the LPE is comparing the same fuel lobe. Move up to a 43% lobe then it flow significantly more than the +10% volume vs a LT4 with a 38.
Lowering the pressure on any pump will lower fuel delivery. The difference here is one is designed to operate at a lower pressure vs the other. You can crank the pressure up on the LT4. I have seen guys run 32-3400 psi. The problem is most aftermarket injectors are not stable at that high of pressure. Only the OEM LT4 injectors can tolerate that high of pressure and it's only going to squeak a little more headroom out.