Pretty burnt out on this one but ill try and put as much effort into the explanation as i can stand to.
Basics: 02 Camaro, Thompson built short block (forged 5.3) with 241 ported heads, BTR cam, On3 single 78mm, pump E85, dual squash in tank with 120# injectors. backed by an 80E.
So this car went back together after the new thompson built bottom end, worked fine thru some base dyno pulls up to about 10 psi, sent it with the owner for a couple weeks to put miles on it. Ran fine until it had a tank of not so good e85 put in it, got that ran out all back to normal. Randomly it developed a break up around 3500rpm, traced it back to the msd 2-step. eliminated that and a new problem was un-masked.
So in short what it does now is right at or around 5300 RPM on a dyno or any high load situation it develops a really bad misfire with very loud cracking out the exhaust side. It will not pull thru it and acts as if it shuts off for a split second in between cracks. During this time frame its taking about 15 degrees of timing, about 15 psi of boost and holding steady 11.3 afr +/- a point. It doesn't show up real well in a log (see attached). On the street when it can spin, goes clean to rev limiter , no problem! Hook it up ona big tire and now its back to popping.
We have tried all sort of things with plugs like .020" gap, as big as .035" tried tr6, br7ef's, more dwell, more timing, less timing, had spring install double checked and actually shimmed a bit thinking it was a valve train issue. 3 diff sets of coils were tried, both car and truck versions, all grounds on engine cleaned and tested (.2 voltage drop) incl making sure pcm ground is separate on back of DS head. Crank relearn with tech 2 was also completed.
I cant find anything obvious as a rev limiter issue causing this or anything major in the calibration that would contribute but its not consistent enough to seem like one. It runs super nice otherwise and is making 600hp already right before it breaks up.
To me it seems like something to do with the crank reluctor or air gap between the ckp and wheel? with how nasty the pops sound it's very much like one i had years ago right before crank wheel ultimately broke.
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