When running out to the upper midwest, sometimes I can only find 91 octane. I tend to make that my target pump gas. I also like to run the Direct Connection vacuum advance distributor. I'd rather run a quick curve and advance the timing where the engine wants with a lower compression ratio than run too high a ratio and have to knock the timing back. The 66 has TRW forged 10.5 pistons, since I wanted to build it as close as I could to the way they came from the factory. It sounds so good with racing gas and the timing at 10* BTDC, but mostly I knock it back to 0* TDC to run 93 octane. My heads were milled .040 and .038 on the intake side. The chambers are @ 57.4 cc + or - 1 cc and are polished like yours, mainly to get all the chambers the same volume. So I tend to shoot for 9.0:1 for pistons on my other cars. On a 273 that means 2 barrel pistons at about zero deck hight.
