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MHP +6.4cc Pistons for S&S 4.250" Bore Cylinders 128/131 cubic inch setups MHP-P4250

Original price $595.95 - Original price $595.95
Original price
$595.95 - $595.95
Current price $595.95

Moonshine Horsepower +6.4cc Pistons are designed to be a direct replacement for 4.250" S&S 128 and 131 setups when running a high horsepower camshafts with larger intake duration on your M8. Need to run with correct camshaft, high flowing ported heads and intake manifold.

Designed to run on pump gas equivalent to 91 octane or greater. 


  • CP Carrillo X-Forgings
  • +6.4cc dome
  • .043 top ring
  • .043 second ring
  • 3.0 oil control ring
  • V-Shaped Accumulator Groove
  • Underhead CNC Milled, Lighten 
  • Shelf Mill, Lighten
  • Double Oilers Per Pin Side


  • 128 cubic inch, 4.250" cylinders and 4.500" stroke flywheel
  • 131 cubic inch, 4.250" cylinders with 4.625" S&S stroker flywheel (works with the stroker setup since the rod is .0625" shorter than a factory H-D rod). 
  • .043, .043. 3.00 S&S ring sets supplied in most S&S Cylinder And Piston Kits and S&S Power Packages


  1. Moonshine Horsepower 588 
  2. Star Racing 3/4
  3. Ward Performance 550

These pistons and cam setups require high lowing ported heads and intake manifolds. We recommend pairing them with our Moonshine Horsepower Street Fighter Heads, MHP-F15H93-NEW and 66mm Intake Manifold MHP-F064


Milwaukee Eight 17 - Current, M8 Engines with S&S 4.250" bore cylinders. Only compatible with 4.500" stoke 128 setup and 4.625" S&S stroker flywheel 131 setups.

Disclaimer: NOT LEGAL FOR SALE OR USE IN CALIFORNIA ON ANY POLLUTION CONTROLLED MOTOR VEHICLE. Not legal for sale or use on any EPA pollution controlled motor vehicle.