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    1. #1
      Join Date
      Oct 2004
      Location
      Delaware, OH
      Posts
      1,379

      GM 572 crate motor problems - need help/suggestions/opinions

      I'll try to keep this brief, but need to list all the things I've tried.....

      I have a brand new GM 572 (620hp model) installed in my '70 Nova. I'm running a Centerforce DF flywheel/clutch/pressure plate, a Tremec TKO 5-speed and 3.42 gear. Running 110 leaded race fuel.

      The engine idles great and when accelerating ANY amount it runs out smooth and STRONG all the way to redline. The problem is when trying to hold a constant mph. When doing this, the engine surges and stumbles, NO popping/backfiring, more of a back-n-forth surge. The mph, rpm or gear doesn't matter, if I'm holding the throttle still it's the same surge/stumble. When stumbling/surging you can hear the change in engine tone through the exhaust which makes it sound like a miss or carb loading up, but it's not.

      I initially thought it was a carb problem when I posted my previous thread (https://www.pro-touring.com/forum/showthread.php?t=20887), but have since ruled that out as a cause. Here are the things I've changed/tried to try and resolve the surge/stumble:
      • Changed the primary jets in the 850 Demon both up and down from baseline - no change
      • Plugged the power valve in the 850 Demon - no change
      • Swapped out the 850 Demon with a BRAND NEW 950 Holley - no change
      • Changed the initial timing from 20 degrees (44 advanced) to 12 degrees (36 advanced) - no change
      • Swapped out the MSD HEI distributor and GM wires with a new electronic distributor and wires - no change
      • Changed the ACDelco plugs for Bosch Platinum plugs - no change
      I've called Barry Grant, my GM Performance Parts dealer, and anyone else that would listen to me whine. I've tried all their recomendations - nothing has helped. PLEASE HELP, I'm open to ANY opinions/suggestions. I'm at a total loss.



      Thanks!






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