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Thread: Weird issue on fresh build

  1. #1
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    Default Weird issue on fresh build

    Here is the issue
    2009 Pontiac G8 with stock L76
    Installed Texas Speed Bald Eagle cam NA
    Beefed internals with head studs, ZL1 Head Gaskets, ZL1 Lifters, Double Spring Valve Springs, Titanium Pushrods. To get it ready for 10 psi of boost from a centrifugal supercharger.

    First start up working with a tuner it was running at 1.2 lamda and would not accelerate under no load. I added some fuel just to circulate the cooling system out then send him a log. He said something does not look right so I checked vacuum and we have 5 in/hg.

    I proceed to smoke test for vacuum leaks, pull the intake and inspect, remove supercharger belt and intake hose and pull from ambient air, hose the vehicle down with flammable brake cleaner watching pids for a spike in fuel trims, pull rocker arms and measure pushrods and they are .025 too long so I order correct length pushrods, I check Overlap on TDC of Exhaust stroke and the cam degree seems to be good and no timing chain issues (Not sure how anyone could mess up an ls timing chain but hey I am human).

    The right length pushrods was the only thing that made a difference and that got me to 7 in/hg of vacuum.
    So my tuner said lets just see if we can tune it to make a couple runs and we got it running pretty well around .8 lamda but still terrible vacuum assist for the brakes and it lopes like a sun of a gun.

    I find out from my tuner it is common for Texas Speed and BTR both to misbox cams and I could have gotten a stage 4 or some humongous cam so I researched and their is virtually no ls cam that would make less than 15 in/hg of vacuum. Then I get the thumbs up from my tuner to push it into boost and see what happens.

    We got 1/2 a pound of boost at 5500 rpms. I should have been around 7 psi at that rpms. The supercharger peaks at 10 psi at 6800 rpms with the pulley I have. Something is wrong, here is a couple things I noticed none of which tell me anything but maybe someone can shed some light.

    When I replace the pushrods all the valves opened instead of the lifters bleeding down, however I have 150 psi of compression at 5k above sea level and a leak down test proved it must just be very stout lifters.
    If the valves where staying open that seems like boost would not be affected as compression would be going back into the intake and honestly the car should not even run.

    The vehicle runs awesome, still only about 400 hp based on some simple math and this combo should be 600+ at the crank and be capable of 10 psi and we got 1/2 a psi.
    I am stumped, my techs with 30 years combined are stumped, my Dad with 30 years is stumped, the tuner with 20 years is stumped. What could possibly be going on? It seems like a massive vacuum leak, how and where if so. I followed instructions and ran a T from the Vacuum booster to the blow off valve. The PCV system is intact and the vent on the passenger side is vented directly back to the air cleaner. It has the EVAP system intact but the purge valve is closed and operating correctly.
    Any Ideas?

    The car runs amazing, pulls just like a healthy cammed engine should but the no boost from the vacuum booster for the brakes and virtually no boost from the supercharger at the rpm levels I have tells me I got a serious problem, but I cannot explain what the heck.

  2. #2
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    Did you measure the pushrod length to get withing preload of the lifters? Is the timing chain indexed correctly?

    BTW, I recall ZL1 lifter are generic ls3. They will not survive with a cam much over stock, Johnson is the preferred lifter for higher lifts.
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  3. #3
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    Quote Originally Posted by jcmGT View Post
    Did you measure the pushrod length to get withing preload of the lifters? Is the timing chain indexed correctly?

    BTW, I recall ZL1 lifter are generic ls3. They will not survive with a cam much over stock, Johnson is the preferred lifter for higher lifts.
    I measured the pushrods with a length checker and a mic so I am confident they are the right length. As for the timing chain I measured overlap and came up right in the middle of LSA on TDC of the Exhaust stroke so unless something has changed there it was dead on. I did spend like 30 min checking and double checking when I assembled the motor to verify timing was on but something just seemed off. I remember one of the valves seeming to opening way too early but I did not have the heads on and when I got the heads on it all seemed to be decent.

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