What is best spark plug gap ?

[grasshopper]

Hi all. Wondering what the consensus is for best spark plug gap for electronic ignition ?
Should it be different for hot street performance engine ? eg, dual Weber set up, warm cams, high comp pistons ?
Also, what is best spark plug for this type set up ?
Thanks.

[SteinOnkel]

I haven't gapped spark plugs in more than ten years. The manufacturing specs on those things is so tight, you are not going to get it any better with those crappy, cheaply made in china discs they sell at the auto parts store.

Run the correct heat range for you engine/application. In order to determine that I would look at a car with similar compression ratio (what is "high" on a Fiat twincam anyways, 10.5:1?). How the mixture is formed is practically irrelevant. In the case of dual carbs, those always run rich. Richer mixture means a colder temp in the cylinder. Electronic or points is also irrelevant, the spark plug does not care how the electricity for the spark is delivered to it. A different coil would maybe affect the choice of plug, but I'd expect the wires to be more critical in that regard. As for the cams...that's not going to get you into a hotter burn. Not with pig rich dual webers anyways.

Buy quality plugs from a renowned manufacturer and don't worry about them for 100k miles.

And stay away from those multi electrode plugs, it's all marketing non-sense.

[grasshopper]

Thanks for your reply ! That all makes sense. Just to clarify about the dual Weber's typically running rich ? I've tried adjusting the fuel mixture on both my Fiat's (both with Idf's). Im finding my spark plugs are turning sooty black at just about any setting. On one of the cars, the engine sounds best at aprox one quarter turn out from lightly seated. Is this normal ? Both cars have typical mods with hot cams,high comp pistons,dual carbs. Ive just read somewhere on the net that the plug gaps should be at 0.30 to 0.35. I've always gapped my plugs at like 0.25. Been having some ignition problems lately. That is why im asking all kinds of questions,,lol

[AndyVAS]

It's always wise to gap the standard style plugs. Platinum plugs and other "fancy" types should be carefully checked but never adjusted.

Points ignition tend to like 0.025-0.028 gap. Electronic ignition tends to like 0.030-0.035 gap. If you want to maximize power you'll need to do some extensive testing while watching AFR and reading the plugs.

[SteinOnkel]

Thanks for your reply ! That all makes sense. Just to clarify about the dual Weber's typically running rich ? I've tried adjusting the fuel mixture on both my Fiat's (both with Idf's). Im finding my spark plugs are turning sooty black at just about any setting. On one of the cars, the engine sounds best at aprox one quarter turn out from lightly seated. Is this normal ? Both cars have typical mods with hot cams,high comp pistons,dual carbs. Ive just read somewhere on the net that the plug gaps should be at 0.30 to 0.35. I've always gapped my plugs at like 0.25. Been having some ignition problems lately. That is why im asking all kinds of questions,,lol

Yes, because they are outdated junk.

As for one quarter turn out from lightly seated, that means your idle jetting is too large. Ideal would be 1.5 turns out. But nothing is ever ideal on these things, see above...otherwise we might still be using them.

Your spark will either ignite the mixture or it won't - your issue is not related to plug gap.