I am running about .003 deck and .040 off the head with 307 flat tops. I get a some knock with reg. unleaded at low rpm under load. Anything after 2000 rpm is ok. With prem. fuel everything is ok. Still using stock radiator (50 Chevy) and have had no heating issues in this Texas heat even with AC on. These little 250s like compression so,squeeze it down,add a little more gas and pony up for some of that hi-test and have some fun...SCRAP
