[jim_howard_pdx]

Eric makes a really good and significant contribution. He says that some of his high compression buddies run HOT plugs to keep them clean.

Eric caught my dis-information and he wins the first award for thinking this all the way through.

A racing plug is always a cold plug?

That is PATENTLY FALSE.

Racing plugs come in all different heat ranges. For a turbo application we tend to keep the electrodes short, because the rpms are so high that the ignition events are packed in very tightly every minute the engine runs. So without a short cold plug, the high heat being generated each minute would literally burn off the center and grounding electrodes all together.

Have you ever seen the picture of a melted grounding electrode? They can look very bizarre. It was the rpm and time that did that damage, not predetonation or detonation.

For an engine with excessive overlap like my 428 with 114 degrees of overlap, I had to run a plug three ranges hotter than stock just to keep the plugs clean.

Sooty plugs will not kill horsepower if the next spark still ignites the mixture. The danger is that every engine misfires, and when they do a sooty spark plug can actually get "fouled" to the point that it will not fire as often as it does fire and that costs you big time.

I had a bad spark plug wire on my 358. We found it when we pulled all 8 plugs to diagnose a detonation problem. One plug had a completely filled space of oil, fuel, and carbon between the center and grounding electrodes. Almost as if you took a spatula and shoved a yuchy mess into the space.

My son was horrified. Worried that a valve stem was leaking oil, or that the rings were damaged or improperly indexed.

I pulled the wire, tested its continuity and found it to be open. We cut off the end near the spark plug, re-crimped the connector and voila.....a perfectly firing engine.

Eric points out a very important point, and that is you need to play with different heat ranges at the track during test events, so you can find the one that best produces the quickest times while also keeping the plug clean.

What is really strange and bizarre to me, Is that a team can build 3 engines for a season, and each might need a different plug. One engine we might build for altitude tracks. One engine might be built for high track temperatures. One engine might be built for a slow track (one that has very poor stick at the starting line). Each of these three engine's might have different cam timing, initial timing, or advance curves. And each requires a different plug.

That is why I say ( AND THIS IS TOTALLY TRUE ) you must establish you ignition curve first, and then tune everything else around that starting point. Otherwise you have no baseline.

Conversely, any time you change any engine tune element, you need to go back to your plugs and see if the heat range needs to be altered to take advantage of your other change.

Man....I lied again....on my last response I said that was all I was going to say about spark plug heat ranges. Guess no one can trust me.......

Eric, thanks for making this thread more fun. I was worried that it would be dull and boring.