Original answer "Unless it's 14-1 or running boost .045 is a good compromise for spark duration and gap geometry." Just be glad he didn't ask what time it is, would have opened that whole space-time can of worms Simple questions have simple answers, this one had no "right" answer, so we run amok with perturbations !!!
So my starting point is .045", for the following motor ? 302 GMC Jimmy out to 324 CI, 5,500 RPM, 13.1 compression at "Bonneville", race gas, head has been ported, HEI ignition with seperate coil... Again, thanks for all the conversation !
From the paper work that I got on my ZZ383 crate motor from chevrolet says .040 It is rated @425 braking HP as I just gaped them today
GM used the .060 gap when they first came out with HEI with the coil in the cap and they were hard on plug wires, distributor caps and rotors. A guy I knew had a 74 pickup and his co-worker decided to mess with him by pulling 2 plug wires off. It wouldn't start, they couldn't get any spark and they ended up putting a distributor in it. I looked at the one they took out and there was a hole burned through the rotor. You couldn't pull a plug wire to check a misfire, even with plug wire pliers it would really nail you or it would burn the rotor.
The Jalopy Journal
