Unleash the MHP 139 Nightmare – Moonshine Horsepower’s 139 Cubic Inch M8 Engine Build, forged for riders who crave peak performance and thrive at 6,500+ RPMs. We redefine power with massive 4.500″ MHP Monster Cylinders and a lightning-fast 4.375″ stroke – an RPM-devouring beast that keeps the piston higher at bottom dead center, slashing flex and strain on the cylinder spigots. This monster demands precision-bored engine cases to cradle our oversized cylinders, featuring centrifugally cast ductile iron sleeves from Darton Sleeves and extended spigots for unshakable piston stability. The larger bore frees up the intake valves for massive airflow, while our MHP Monster Heads with oversized +2.5mm intake valves and square ports pump out relentless flow. Matched with our MHP Monster CNC intake manifold, the MHP 139 Nightmare delivers unrivaled power and superior ring seal thanks to the shorter stroke. With reduced piston speed and less rod angle compared to a 4.500″ stroke, this setup eats RPMs for breakfast.

Check out our dyno sheets below to dial in the camshaft and exhaust setup that suits your ride – because nightmares don’t just haunt, they dominate.