I would DEFINETLY run premium pump gas in it especially if your bumping the timing! Lots of variables (bore size, altitude, domes, timing , jetting , porting, etc.etc.) when it comes to compression and what gas to run. Normally if jetted correctly i can run prem. pump gas up to about 160-165 lbs of compression WITH a GOOD compression guage like a Snap on . Just my .02