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Message: <blockquote data-quote="96blak54" data-source="post: 1587493" data-attributes="member: 14727"><p>Premium gas vs E85 is a night and day difference when used in an an engine built for E85. Long story short about the 18.1 compression engine I built (intended for E85) I first started the engine on premium gas just to see where the point of intolerance was. Hoping some operation rpm was possible. The engine would idle and rev, but once to temperature the idle would run off erratic to high idle and temps would keep climbing. I drained the tank, dumped fresh E85 in and got the engine running again.....no other changes. The idle was perfect, rev was super snappy, engine sounded link something of a nitro dragster and now engine temps stayed cold and struggled to get to a normal operating temp of 190-200. Im sure a simple thermostat swap would have helped, but I was eager to get the car tuned. Got it tuned, drove great, engine was not tame and sort of scary touchy. If i remember correctly, the forged pistons I used to achieve that compression ratio were made for a propane drag car that I purchased used from Shelby America. I was having oil consumption because I modified the 2nd oil ring groove to accept a standard modular ring with the dimensions for standard groove from standard pistons. In short the piston crown wouldnt grow enough to push the ring against the cylinder walls due to very low in cylinder temps. So I ditched the 18.1 pistons in favor of stock flat tops that brought the compression down to 13.1.</p></blockquote><p></p>