Hey guys. I have discussed this problem on here before, but I still haven't figured it out. In my pace car, I installed a fresh 331 stroker. Aluminum heads. Right around 11:1 compression ratio. Carbed. A local machinist, who has always done good work for me, did the machine work, balanced everything, and assembled the short block. I finished the top end and did everything else. When I first fired it up (a couple years ago) it had a backfire whenever you get in the throttle and let off of it. It would happen while driving or parked and revving in neutral. The car wouldn't hardly run without advancing the timing further than normal. About 30 degrees initial timing (distributor not locked out...this happens with oem and MSD distributors, as I've tried both). I've installed 2 different MSD 6AL boxes, a duraspark 2, and currently, a Pertronix Digital HP.

Yes, plugs are wired properly according to the Comp Cams spec sheet. After exhausting all avenues, I decided to pull the timing cover today and check that the cam is clocked properly. It is. At one point, I thought I had it figured out. I fixed a couple header leaks and it seemed to not be as bad, but never went away. I've had 3 or 4 different carbs on it, including pulling them from other good-running cars. It currently has a new Quick Fuel Brawler 650 on it. I've adjusted the idle mix and rejetted to where it's running correctly. I even installed a wideband to confirm and fine-tune.

I'm pretty much at my wits end here. I guess it's possible that I still have a small exhaust leak somewhere, but this isn't an annoying "pop" on deceleration. This is like a shotgun going off. A buddy suggested that the compression ration may be higher than what my machinist figured up, and that the 93 I've been running might not be enough. But it doesn't seem to be a pre-detonation problem. If my cr is too high, could it cause a bad backfire like this?

Other things I've tried are a compression test, new/different plugs, plug wires, and several other things I'm probably forgetting. What am I overlooking here?