Inliners International Forums General Discussion Hi Performance 261 compression ratio

You are at that cross roads of towing vs racing and it is of course going to be a giant size compromise no matter what. Stock 261 motors were spec'd at like 7 to 7.5 for a compression ratio depending on the casting head that was used. One head had a 86.1 cc combustion chamber the other had a 95 cc combustion chamber. The 261 piston sat like .110 or better in the hole, a good bit lower than the 235. The low compression was specifically designed for big truck use, dump trucks, oil delivery trucks, at low rpm. So to get the compression up a bit, lots of people over the years used a 59-62 848 passenger car head that has a 79.1 cc combustion chamber which might get you to 8.0 with stock pistons, maybe. To get the compression higher, you need flat top pistons that are at near 0 deck height, or pistons with a big lump on the top and near 0 deck height or at lease in the hole at the same level as a 235. Ross sells these kinds of pistons, mine are from venolia but I think Ross has a better pattern. I am probably at 10:1 maybe 10.5 compression ratio and use premium gas, no pinging, but also no load other then the car itself (57 chevy). So this is a hard call but I would think that 9:1 would be safe for the dual duty you want to engage in. Just my own personal opinion and thoughts.