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The heads will get new guides, +1mm intake and +1mm exhaust valves and a performance valve job. These kits feature our 4.280 bore cylinder kits with our custom liners, made from 110,000 PSI ductile iron. These are made longer to support the piston at the bottom of the stroke.
The Stage IV kit consists of: All-new Screamin' Eagle ® Extreme CNC-ported cylinder heads, 68mm throttle body and new cast 68mm intake manifold, new SE8-550 high-lift cam and 6.8 g/sec fuel injectors work together to feed the engine large volumes of air and fuel to help maximize power.
136" & 131" Big Bore Stroker Cylinder & Piston Kits for 2017-Up M8 models. Huge displacement increase (4.320" Bore) means a huge power increase. Works with stock crankcases. Original engine serial numbers are retained. Powder coat finish matches factory finish.
This performance kit increases your Harley-Davidson M8 engine’s torque and horsepower by over 60 percent. It runs on pump gas at 11:1 compression making it a big-inch motor upgrade that provides both consistent and dependable naturally-aspirated horsepower as well as massive amounts of torque.
CSR 128″ High Compression Big Bore Kit for Harley M8 Models (114/117″ to 128″)
The latest kits combine our biggest big bore cylinders (4.32") with matched cam/cam plate/oil pump and everything else a high performance cam chest needs to make big, reliable horsepower. Transform your 107" to 129" and your 114/117" to a 132" monster.
2017-2023 Harley-Davidson® M8 touring models (oil-cooled) Features & Benefits. Cylinder Heads. High-flow cylinder heads with premium seats, guides, valves, springs, and seals +1mm oversized intake and exhaust valves; Valves are .030” longer than stock for improved valve-train geometry.605” max lift valve springs
