467-Ratman

Was wondering if a larger spark plug gap would increase the heat range of a plug. I have mine gaped at .040 now and my MSD instruction manual said to gap the plugs between .050 and .060. Will that produce a hotter spark or just a larger one?

comp

no, opening the gap exposes the spark to more of the air fuel mix

467-Ratman

Dumb question, but does that make for a more complete combustion cycle?

lars

467 -
Westech Peformance in LA (the outfit that does all the dyno testing for Hot Rod/Car Craft/ Hi PerfChev, etc.) has a really neat distributor machine with a spark plug tester. I got to play a bit with this machine last time I was out there doing dyno runs with Hot Rod, and I found out the same thing that Westech has known for years:

This machine allows you to pressurize the spark plugs to simulate cylinder pressure while the distributor fires the plugs. Little "windows" allow you to observe the plug sparks at elevated cylinder pressure. What I found is that gaps in excess of .040, even with an MSD system, will cause the plugs to begin misfiring at peak cylinder pressures and elevated rpm (or the arc will jump the plug wires). Big gaps work well on low performance engines that do not produce high power levels (high cylinder pressure). But high compression, high power engines do not perform reliably at elevated rpm with big plug gaps. For this reason, Westech and Dougan's Engine Service run all their engines at .035 - .040 gaps. This produces reliable spark and ignition throughout the rpm range with low possibility of misfire. Larger gaps will either not fire the plugs at all, or the spark will arc across the plug wires at elevated cylinder pressures.

...just the facts as I have personally observed them with some good testing equipment...

Sharky Guam

That's cool lars....I have beleived the same to be true for years. When I was in college, we studied the effects of plug gaps to varying engine designs. And what we found back then with 1980 technology seems to still apply in this modern era. I was recently working on a newer Mustang with modern electronics to control engine spark duties and experienced a mid to high rpm misfire. After regapping the plugs a little closer, the misfire went away. Performance was not negatively affected in any way by the closer gap. So that proves that theory to be right on the money.

Solid LT1

Big gaps also KILL plug wires and increase chances of crossfire on parallel plug wires. I run 0.040" on my Accel 300+ ignition.

467-Ratman

Lars, as usual thank you for the very interesting info about the plug gaps. Very nice to know that bigger gaps are not going to produce more power...

big632

028 to 030 gap on anything making any kind of power,oterwise the volume of fuel and air,cylinder pressure will shut down the spark.

Desertdawg

Thanks Lars.

I ran into this with my non stock fuel injected 460 a few years ago, It ran the best with stock plug gaps, I found this out after pulling and regapping them 4 different times. :banghead: