These high compression 3-1/2" bore forged stroker pistons for 1984-'99 HD^® big twins are a high compression option for 89" stroker kits for 1984-'99 with 4-5/8" stroke flywheels and S&S^® Super Stock heads. 12:1 compression . These pistons may also be used in stock stroke 1200cc HD^® Sportster^® models with S&S^® Super Stock heads.10:1 compression. +.010" oversize.