Be honest>

[turbomangt]

If I change my spark plugs at say 30,000 miles, to one of those so called high performance ones, will I really notice a difference? Gary

[Mike Radowski]

Just changing your plugs at 30,000 you will probably notice a difference. They won't even have to be the performance plugs. If you have that many miles, it might be a good idea to put on a set of performance plug wires, also.

Mike

[98 Neon Driver]

You gotta be careful as mopars can be fussy w/ their plugs. I tried using Bosch Plats in my neon and the thing ran worse, tossed in the cheapy champs and the car ran like a champ

AC

[MX-5]

The Champion copper plug will ignite 100% of the fuel. There isn't any unburnt fuel to find hidden horsepower.
New plugs will certainly be better, but only because they don't have 30K worth of wear on them.

If unburnt fuel was getting expelled through the exhaust, you would get several trouble codes and a check engine light.