S&S Cycle 4" big bore cylinder and piston kits boost 88" Twin Cam engines to 100" These bolt-in kits don't require any machining, rebalancing or engine removal, and include just about everything you'll need to complete the installation The biggest cylinder bore that can be installed in a stock crankcase without machining! Bolts in No machining, balancing, or splitting the crankcases Complete kits include cylinders, pistons, gaskets, and instructions Matches stock finish Set up for 4" stroke 4.937" Cylinder length Forged piston Compression ratio: 79cc S&S Cycle heads will be 11.3:1, 83cc heads will be 10.8:1, 85cc heads will be 10.5:, and 89cc S&S Cycle heads will be 10.1:1 Match with S&S Cycle 585 cams, Power tune Headers, MK45 mufflers and a S&S Cycle Stealth air cleaner for the best possible performance