Anyone here ever have their pistons machined?

I can't say for certain as atmospheric concerns may've been the big problem, but a friend of mine a few years back had his Mustang tuned in San Antonio for 91 octane fuel...it ran 12.50s all day in the Texas heat with no detonation whatsoever. He PCSd to SoCal and 91 octane there pinged like crazy. He said the only way to keep it from pinging above 50% throttle was to pour in additives at every fill up or pedal it out like a butler everywhere he drove