Interesting, these sparkplugs claims up to 12% increase in HP

These were not for horsepower, but reliability---and is the overwhelming reason on aircraft, NOT HP

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You'r CORRECT, HOWEVER, if you have ever been in the air, and switched from mag to mag.......... You will notice the RPM drop..............

Dads 0470 will drop about 50RPM per mag, and 150 under full power, sure you could back off the pitch some at cruise and retain the RPM, but the full power is with a flat prop..... Thats HP.

The magic spark plugs aren't worth discussing, splitfires have been detonating for years...............