These 3-7/16" .020" bore, low compression stroker pistons are part of an S&S stock bore stroker kit for 1936-'84 HD big twins, and are designed to be used in conjunction with S&S stroker flywheels. Flywheels of the following strokes may be used for the following displacements: 4-1/2" stroke - 84" @ 7.3:1 compression 4-5/8" stroke - 86" @ 8.0:1 compression 4-3/4" stroke - 88" @ 9.0:1 compression These pistons are normally used in stock HD cylinders, and must be purchased separately, based on the required piston oversize. The modern alloys used in these pistons, coupled with the advanced skirt profiles, allow them to be fit tighter resulting in low engine noise and long engine life. In the past, this could only be achieved with weaker cast pistons. Cylinders are available from S&S for 1941-'47 and 1966-'84 models. S&S offers machine shop services through the S&S Service and Speed Center. New pistons can be fit to your existing cylinders for a reasonable charge.