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MHP 4.250" bore High HP Complete Upgrade Kit - Oil Cooled Heads - MHP-5050

Original price $3,389.75 - Original price $3,389.75
Original price
$3,389.75 - $3,389.75
Current price $3,389.75

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. We have paired these pistons with our MHP Street Fighter +1.5mm Valved heads, MHP-588 camshaft and 4.250" bore 0.040" thick Cometic Head Gaskets for a complete upgrade kit to your S&S 4.250 cylinders (128 &131 setups) or upgrade your 128/131 S&S power packs.  

Dyno sheet shown is a 128 4.250" and 4.500" with this complete setup. For more information please call the shop at 615-274-4170 and ask for Nick Zinola, Aaron Staudinger or Jamie Lima ONLY. 

PISTON FEATURES; 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

These pistons and heads work best with a high flowing ported  intake manifold. We recommend pairing them with our Moonshine Horsepower 66mm Intake Manifold MHP-F064

HEAD FEATURES; Moonshine Horsepower New +1.5mm Oversized Valved CNC Ported M8 Heads 93cc Combustion Chamber by Frankenstein Engine Dynamics - These are the heads we run on our MHP Ass Eater 131 setups.

  • No cores needed for this head option
  • Heads are fully assembled and ready to bolt on your build
  • Stainless Steel Intake valves size 1.630"
  • Stainless Steel Exhaust valve size 1.285"
  • High- lift springs good to .625" of lift
  • Titanium Retainers
  • CNC steel triple groove locks
  • Intake flow 413cfm @ .600" lift
  • Exhaust flow 260cfm @ .600" lift
  • 160 plus horsepower potential 
  • Heads do not come with exhaust studs

Camshaft Features: Designed to have an aggressive torque curve that comes on strong and gradually increases to max torque near 4,900 rpms. Typically peak horsepower is achieved around 6,500 rpms. This is one hot camshaft when paired with the correct parts. 

  • Most lift for reliable performance
  • 2400 to 6600 RPM Range
  • .588 Lift, Intake Closes at 44 degrees
  • Great for 124-135 cubic inch setups
  • Awesome torque curve and still unleashes the top end HP
  • Amazing lope at idle

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.