These Big Bore cylinder and piston kits in combination with the separate available 4 5/8" stroker crankshafts enlarge the displacement of your M-8 engine to a massive 131CI (2151CC) for the 4.250" kits or 136CI (2229CC) for the 4.320" bore kits. A huge displacement increase means huge power increase. Cylinder kits and crankshaft work with the stock crankcases and retain the stock engine height. The powder coat finish matches perfectly with the OEM engine finish. Cylinder kit includes two cylinders, two pistons, two pins, four clips, two ring sets and head-, base-, and exhaust port gaskets. Also included is an exclusive S&S 131CI or 136CI cam cover badge. The 4 5/8" stroke crankshaft must be ordered separately for all applications. Pistons work with both OEM style tapered wrist pin ends or High Performance full width piston wrist pin ends. As the stock cylinder head bolts are a single-use design you will also need eight stock style head bolts or a set of re-usable S&S High Performance head bolts. Fits all Touring & Trike 2017 to present (except 121CI VVT) and all Softail 2018 to present.