Were you experiencing pinging? If so, you could back off the timing, as in not run it too advanced. Start backing it off and the pinging might/should go away.....depending on what engine mods you have done. You will lose some power, but the pinging generally will stop. I try to run my Ford as advanced as I can. When it starts to ping, I either have to put higher octane in it or back off the timing. The "pepiness" of the motor goes away too though. Your better off just running the premium if it has been happy all along.