These big bore pistons work with the stock 4-3/8" stroke flywheels to convert any 2007-'16 HD® big twin engine from 96" or 103" to 107" displacement with 10.4:1 compression with stock heads. Stock cylinders may be bored to accomodate larger pistons, but we recommend S&S 3.927" bore cylinders which feature high strength alloyed cast iron liners. Pistons are compatible with stock rods with tapered wristpin ends. S&S® 3.927" bore pistons are machined to such close tolerances that it is not necessary to measure the piston. Just bore cylinders to nominal diameter +/- 0.0005" for correct clearance. Additionally, the low friction coating on the piston skirt makes taking measurements very difficult. 3.937" standard bore.