3 5/8" BIG BORE CYLINDERS AND PISTONS FOR EVOLUTION BIG TWINThese 3 5 8" pistons convert your Evolution Big Twin motor to 88CI (1475CC) and 9. 25: 1 compression ratio when used with a stock stroke crankshaft and with stock cylinder heads. Piston kits come include pistons, rings, wrist pins and circlips. You will have to order two 3 5 8" Big Bore cylinders and a piston kit separately. As with all 3 5 8" Big Bore cylinders for Evolution Big Twin the crankcases must be bored to accept these cylinders.