My KCR 427W has 612 hp, & a pretty snotty cam in it. I always run premium (91 octane in Cali) but occasionally have problems with dieseling (run-on). I dump a bottle of the cheapest octane boost I can find (typically Gumout octane boost at Walmart) with each fillup... seems to help. I don't expect any performance enhancement, but it does seem to help with the dieseling in hot weather. I realize it may be purely psychological, which is why I don't invest a whole lost of money in it.
