I've just installed a Pertronix III and a Flamethrower III coil into my 482 Stroker motor. The points conversion I removed was the single wire Breakerless SE conversion using the factory coil and resistive wire. A link to the complete install is below but, my question has to do with spark plug gap. My motor has the TA Stage 1 SE Aluminum heads with NGK FR5 plugs gapped at .035. The Pertronix coil delivers 45,000 volts to the plugs vs who-knows-what from the factory coil. https://www.v8buick.com/index.php?t...-your-buick-today.372567/page-98#post-3480927 So from those who use the Pertronix II or III with the hotter coil, is it wise to increase plug gap to say, .045 or more? The Pertronix engineer wasn't very clear on this question but he did say the mixture "might" burn cleaner. So, what are you guys using?
You never want to go above .045" even if you have Gods lighting from the heavens to fire your plugs Try each at a track test & tune one day since other then dyno time its the only way to answer your question.
.045 is a good safe gap with electronic ignition. If you had forced induction, or nitrous, that would require a lower gap, but for 10:1, .045. The FR-5 comes pre-gapped at .039. NGK says it is OK to open or close the gap no more than .008. https://ngksparkplugs.com/en/resources/5-things-you-should-know-about-spark-plugs
...and beware cheap-junk aftermarket coils sourced from low-wage countries, and marketed with fancy names and colorful labels.
A custom HEI,or something like what you have can go up to .045” and see some benefit. However,if you run an MSD box in the system,you need to keep it down around .032”-.035”.
Really? I'd have expected an MSD6 or higher number to produce more potential voltage than an HEI, leading to larger allowable gaps. (Somewhat depending on the ignition coils used, and the quality of the insulation in the ignition secondary circuit.)
Msd 6 and higher plug gap depends on static compression ratio. According to MSD, Ray's motor could go all the way to .060. I have pretty much run everything at .045, put dozens of motors of all descriptions at full load against the water brake at 3500-4000 rpm, and never had a spark plug gap related issue. Read the instructions: https://documents.holley.com/6520.pdf JW
I’ve seen it night and day where it was just the plug gap. A variety of compressions,engines,distributors,etc. Maybe you found some that weren’t affected,but just don’t ever rule it out. I should also note that regarding the Pertronix units, a lot of us have found issues show up on the engine dyno and chassis dyno that one might not ever notice just driving their car. They are a good unit and have their place in the market,but they aren’t perfect.
I have used larger gaps than that...on "daily driver" engines in particular that have manufacturer-specified gaps of .060-ish. I experimented with big gaps on performance-oriented engines in my youth, and got bit a couple of times which pretty-much took the bloom off of that rose. At the same time, I'm suspicious of any gap larger than about .045; and don't get me started on Oldsmobiles with factory-recommended .080 gaps. Aside from anything happening in-cylinder, I figure there's no real reason to torture the secondary insulation--ignition coil, cap, rotor, plug wires. I don't have concerns about the spark plugs IF (big IF) they've got some dielectric grease between the porcelain and the plug boot. It is worth checking the porcelains, though--sometimes there's dark streaks from the plug terminal down the porcelain to the plug shell, and that's a result of flash-over which is NOT good. '96-2000+ SBC "Vortec" engines and the related V6 "Vortec" are infamous for failing the distributor caps; in particular the cylinder attached to the conductor that bends around the center button inside the cap. The insulation fails, then the sparks go to #3 instead of the cylinder you're hoping will fire in it's sequence. Cheap distributor caps--including replacement ACDelco--have a high failure rate.
