S&S Cycle 4" big bore cylinder and piston kit boosts 88" Twin Cam engines to 100" Bolt-in kit does not require any machining, rebalancing or splitting the crankcases The biggest cylinder bore that can be installed in a stock crankcases without machining! Complete kit include cylinders, pistons, gaskets, and instructions Set up for 4" stroke 4.937" Cylinder length Forged pistons Compression ratio: 83cc CNC Ported Stock Heads 10.8:1, 85cc Stock Heads 10.5:1, 89cc S&S Heads 10.1:1 Matches stock silver finish