Zipper’s MUSCLE 128″ – STAGE 3 Kit for the 114-117″ M-8 is the most powerful top end and cam kit we’ve ever produced for a production motorcycle! The big breathing 4-valve heads on the M-8 engine just love displacement, so we’ve developed this kit for use with our new 4.250″ bore drop-on cylinder. These cylinders are fitted with flat-top forged pistons and topped off with Zipper’s STAGE 3 CNC headwork performed on your cores. Our Red Shift 552 cam delivers HUGE torque as soon as you open the throttle, and carries it across the RPM range to provide instant acceleration from any RPM.
Components included in the MUSCLE 128″ – STAGE 3 kit: * Zipper’s 4.250″ Cylinder & Piston Kit * Zipper’s STAGE 3 CNC Headwork (on your cores) * Red Shift 552 Cam & Bearing * Quikee Pushrods, Covers & Tappet Cuffs * Top End & Cam Gaskets, New Headbolts
Compression is set to a relatively modest 10.9:1 with 225# cranking compression – same as stock, so starting is not an issue. It has an amazing sound at idle and under load, with 67 more horsepower than a stock 114 or 117, peaking at 5,800 RPM. Peak torque starts at 2,800 rpm – 50 pounds more than stock, staying at nearly 150 ft/lbs for over 2,000 RPM, right where you ride! This super-flat torque curve delivers sport-bike-punishing instant throttle response at any RPM, allowing the bike to be ridden like a stocker when desired – But what fun is that?
An EFI tuner, performance exhaust, oversize throttle body, injectors-intake will be required to achieve results shown

Requires YOUR Head Cores to be shipped to Zippers for CNC Porting and other modifications.

When ordering Zipper’s Engine Kits, Head Cores or Exchange Heads may be available – Start a Build Sheet right away to confirm availability.

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.

*To ensure you enjoy a premium experience, Please fill out a Build Sheet/Job Order Sheet prior to completing an order on the website.
Click here for Zipper’s Build Sheet/Job Order Sheet

Weight 1 lbs
Country of Origin

Engine Type

Fuel / Air



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