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Cars falls on its face at 5k RPM

This is a discussion on Cars falls on its face at 5k RPM within the Forced Induction forums, part of the LSx Technical Help Section category; I'll keep it simple: Procharged C5, ran fine on 4lbs 480/420. Broke a timing chain, replaced U/D pulley with stock ...

  1. #1
    Join Date
    Aug 2005
    2000 Corvette

    Cars falls on its face at 5k RPM

    I'll keep it simple:

    Procharged C5, ran fine on 4lbs 480/420. Broke a timing chain, replaced U/D pulley with stock balancer for more boost. RETUNED. Car made 523/480 on the dyno but does not run right now. Hesitates and makes a noise when it goes over 5k. Under 5k rpm drives fine, decent gas mileage still, no driveability issues. Just got my boost gauge and fuel pressure gauge. Boost shows about 6 lbs at 5k so no leak that I know of. Waiting on an adaptor for the fuel sender. So am I running out of fuel? I hope it is that simple.

    This is what I have been told could be my issues:

    Boost leak, probably not since 6 lbs at 5k
    Fuel- pressure by incorrectly installed BAP, dirty filter, old fuel pump
    piston slap- this by my tuner, don't think this is my issue
    blowby- broke timing chain trashed valves and marked up the pistons, may have damaged skirts.
    tuning in general

    Once I get the fuel pressure gauge on I will know better and post up the results. Really want to go forged but just no money for that now....

  2. #2 Tuner Frost's Avatar
    Join Date
    Jul 2007
    Richmond VA
    2,415 Sponsor
    GM Tuner

    You are almost certainly maxing out your MAF at that HP level, and prolly right around 5K. If your tuner kept your AFR to 11.5 across the board in maxed-MAF territory on the dyno, there will be times when it will be too lean up top, since there is no airflow measurement available. Post a prinout of the pull with AFR. Really need a wideband at that level to keep an eye on things. Are you using methanol? My money says the fueling is off up top personally, though it's just a feeling.

    Blowby comes from bad ring seal, which is usually from knock/high cyl temps at your HP level, and usually signals the beginning of the end. Start the car and let it idle, pull a breather/PCV out of the valve cover and see if it "puffs" a lot at idle. Outside of that, obviously compression test and leakdown check are in order.

    I would be unsettled by being told piston slap is the cause by my tuner; that's a new one on me. Never even heard slap much north of idle before.

  3. #3
    used and abused at wot ibanez7's Avatar
    Join Date
    Aug 2005
    Crystal Lake IL

    2001 Camaro Z28 M6

    agreed with above..

    does sound like a fuel delivery issue.

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