Re: Spark Plug Gap - 1972 Chevelle 350, Point Type Upgraded To HEI
I own an early Safari Van with 4.3 V6 and stock HEI, and that specification IS .035. But, with every other HEI I have, the gap is set to .045. The key is, if the compression ratio goes up, drop the gap down.
GM made a real mistake with HEI performance during their Oldsmobile years, they specified a spark plug gap of .060, and even later, .080. This was done to make sure the molecules of fuel could bet in between the plug gap, to get lit off, because the mixtures were so lean, those fuel molecules got further apart from the leanness. The gap had to be giant in order to get enough fuel molecules into it, to get the light off done. GM found that the giant gaps were killing many, many electronic components, namely coils and modules. So, the lesson learned is, stock compression ratios, .045, higher performance comp ratios, drop the gap, and don't gap your plugs larger than .045, no matter the coil, module, etc.