Spark plug gap? .035 or .060??? Help
- Thread starter 87gbodydanny
- Start date
I see .060" as the 3.8 gap. They used a very wide gap with low compression engines and HEI ignitions.
Low compression engines like wider gaps to generate more heat since heat of compression is lower. Basically you want the smallest gap to accomplish clean running.
Make sure your ignition system is up to the task. It SHOULD be if in good shape, but the wider gaps also put more strain on the distributor components. I'm for running 0.045" all day long on Olds 307s and seems to have no ill effect on performance or modules. This is smog dog stock so if you've done mods, you need to make any necessary accomodations.
I believe around .035 for point distributors and 0.60 for hei. Pretty sure a HEI distributor throws a hotter spark so a wider gap can be used.
Just not too wide. Or you'll toast the module sooner than expected. 85 and older 307 with AC R46SX plugs were gapped to .080 from the factory. Along with other engines and makes/models. Module replacement was rampant and the decision was made to come out with the R46SZ plug pre-gapped to 0.060" to "fix" that issue.
The GM HEI is one of the strongest stock ignition systems ever made. The coil is able to produce up to 25k volts and the average in-tune smogger engine only needs between 10k and 20k to perform perfectly. The spark will jump any gap you choose. The bigger the gap, the more energy it takes to jump, the hotter the spark. So a big gap is actually producing a much more powerful spark. That ignites more air/fuel mixture for more complete burning, as well as keeps the gap cleaner. On bench testing I have gotten the HEI to jump a one foot gap. You read that right. As I spun the shaft I slowly pulled the ground away from the carbon button on the inside of the cap. The spark jumped one foot, looked and sounded like a little lightning bolt. If you have ever been bitten by an HEI spark you know what I mean.
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