These Big Bore cylinder and piston kits in combination with the stock 4 5/8" crankshaft in 2023 to present 121CI VVT engines or separate available 4 5/8" stroker crankshafts for other 2017 to present models 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. 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 and all Softail 2018 to present.