Newly Built BIG BLOCK Popping- Causes?

[blklblsk8tr13]

I just dropped a 462 in my 71.

~ .620 lift Hyd. roller cam,
~1.7'' roller rockers
~compression around 10:1 (I think....).
~850 CFM Holley double pumper
~2'' primary tube headers with 3.5'' collectors
~3'' bent exhaust with Spintech mufflers


For some reason this motor pops on one of the cylinders (I don't know which, but sounds like its the same one every time) when I put it under load. All header bolts are tight. I put 112 octane in it to rule out detonation. jets on carb are 80 front and back. Ignition, plugs, wires are new. It does have a Pertronics kit in distributor for a stronger spark. 25 Autolite plugs.

Dyno showed it is running slightly rich to 5400 RPM. I have no idle fuel mixture due to the machine not being able to pick up a signal at idle, I assume because of a lack of pressure through the tubes.

It also sneezes air and fuel back up through the carb every once in a while, I don't know if that is related.


ANY KNOWLEDGE IS APPRECIATED. I'm looking to put my 100 shot on soon, and I cant do that in good faith with something popping.

Thanks,
Eric