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Discussion Starter #1
Not that plugs are the most interesting things in the world, but there's definitely more to them than just gap and go.

Explains what "colder" plugs mean, whether you should increase or decrease gap based on performance mods, etc...

And I came across this little gem as well.
Insufficient spark plug gap can cause pre-ignition, detonation, even engine damage. Too much gap can result in a higher rate of misfires, noticeable loss of power, plug fouling, and poor economy.

When you raise compression or add forced induction (a turbo system, nitrous, or supercharger kit), you must lower the gap (reduce gap about .004" for every 50 hp you add on an V-8 engine, for a Harley-Davidson V-2 engine every 12.5 hp you add). However, when you add a high power ignition system (such as those offered by MSD, Crane, Nology,) you can open the gap back up about .002"-.005".

As an example, let's use a hypothetical `96 350 Chevrolet LT1 engine build-up. The standard gap is .050" for an un-modified LT1. We'll add 150hp Nitrous, so we must lower the gap about .012" to .038". We then decide to add that killer MSD 6A/Crane Hi-6 box and, using our guidelines as outlined above, we can now open the gap up .002"-.005" to about .040"- .043". By following this basic guideline should get you very close.

Further experimentation may be necessary, but by always starting with a larger gap than it thought necessary to reduce the risk of detonation, you should be safe.
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I recently installed the Screamin Demon coil and wires, and am researching whether or not I want to open the gap up any more than stock. The car definitely seems to be running smoother already.

[ 01-27-2003, 06:11 PM: Message edited by: SlickShoes ]

Driver > Car
23,988 Posts
the first link doesn't work, but thanks.

is the 0.004" applicable to the smaller motors as well?

50hp on an LS1 with FI is much easier than 50hp with a zetec.
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