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Thread: Low side drop while Rail & Injectors on point

  1. #1
    Potential Tuner
    Join Date
    Jun 2019
    Posts
    1

    Low side drop while Rail & Injectors on point

    I've always been lurking in these forums and decided to finally create a thread and would love some input from you guys. So here's the current situation that I'm trying to wrap my head around... With my LT4 swapped blower/fuel on my 1LE the logs show I decrease of Low side from 70 all the way to low 50's even high 40's by redline. However, my Inj MS is still at around 4.8-4.9 and mi rail press never drops under 2800psi... This is with E65%!! by the way... everything looks like we can maybe reach E70.... but never seen that before on any stock LT4 fuel system...

    1) What explanation of such a low low fuel pump psi but still being able to have the high side more than sufficient?
    My common sense says less low side = less high side. But maybe I'm seeing it wrong.
    2) Would a BAP put the low side up there in the 70psi and keep it there or Is this an "about to go bad" pump? Keep In mind I have a 1LE which comes with the LT4 intank and I have about 40K miles running full E85 from my N/A Days
    The majority of ZL1 intank pump cars that I've seen keep there pressure in the high 60s and 70s no matter what rpm they are at...

    Thoughts?

    2017 Camaro SS 1LE
    MODS:
    Ported TB/Intake/Headers/Exhaust & the LT4 Blower/fueling @ 8PSI
    Flex Fuel @ E65%
    Attached Files Attached Files

  2. #2
    Advanced Tuner
    Join Date
    Aug 2014
    Location
    Central, LA
    Posts
    737
    The simple answer is that the high side pump doesn't necessarily require as much as is commanded from the lowside to retain high side pressure, but in an ideal world you would supply more lowside to give it an easier time.