Silver finished cylinders. Bigger is usually better when it comes to performance. This bolt-on big bore Sidewinder kit is as big as possible; without requiring additional work. No need for engine removal; splitting and boring the cases or even re-balancing the flywheels. Just swap the stock cylinders and pistons for these S&S 4" big bore parts and you''re ready to rock with 100HP! (note). 4" bore for stock 4-3/8" stroke. 10.5:1CR with stock heads. Forged .75" pop-up piston. Fits stock 96/103" models with stock 4-3/8" stroke. Note: S&S measured 101.39 HP and 118.92 torque. They additionally used S&S 585 cams; Power Tune headers; slip-on mufflers; the stock EFI throttle body and a S&S Stealth air cleaner. Note: Not for use with S&S 79cc cylinder heads.