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Guys I have a 1968 429 ( thunderbird engine ) in my 65 f100. runs great. I have HEI distributor and good wires. new autolite 45 copper plugs. I have them set to .045 gap. is that too much. i also have dual 2.5 exhaust with glasspacks. 3.5 gears in 9" rear. c6 trans. I am curious if thats too much gap in the plugs and if anyone has a similar engine and has experimented with plug gaps. Also running premium gas. Thoughts?
Don't have one right now but I have had several in the past. If that engine is stock you should be around 10.5-1 compression and should be OK with .045 gap as long as the rotor and cap aren't showing signs of arcing. The stock gap was .032-.036. Just keep in mind that as the compression ratio goes up it takes more voltage to jump that gap. We used to pressure test aircraft plugs in a Champion spark plug tester that applied a constant 8KV and a new plug that would fire just fine at 120psi would start to become intermittent at 140psi and would stop firing at all around 160psi. I run .036 gap in my Cleveland and it is 10.2-1 compression ratio and my cranking compression is 162-165 PSI. That is with a Duraspark distributor a Pertronix coil and FBO ignition box.
If you look at engines thru the 70's you will notice that as the compression ratios went down the recommend plug gaps went up. Also there is no real performance gain in an electronic ignition over a well maintained and properly calibrated points ignition up to around 6000rpm.
