Much confusion about octane. Measures ability to compress fuel mixture without premature detonation. Does NOT measure "burnability" or any other characteristic. Stock PRV is 8.8:1 compression ratio. Certainly higher than some cars produced today, but not high enough to require premium grade. I shoot my spark a little closer to TDC than factory spec (high energy ignition), so burn 89 octane to avoid ocassional valve clatter. For comparison, have a 1969 Lincoln with 11:1 compression. Will not run on less than 97 octane (added by the bottle). Bill Robertson #5939