On a stock car it wouldn't do much. On a modded car with the right coldness(lack of the right terminology) and the right gap alot of hp can be had.
IE turbo civic on stock plugs, 240hp, turbo civic on coppers gapped to .40, 280hp...
Diff between copper and platinum is price... copper needs to be replaced more often than the platinums.
Colder plugs makes it harder for the car to start but a 7 shouldn't do much.
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Learn how to use the feedback system! When people don't fallow through with a deal, fucking make it known! of course everyone has all positive points, no one fucking gives negatives for flakers, if you start giving negative feedbacks for flaking maybe people on tr will stop making stupid ass posts about wanting to buy shit then not showing up for the shit.