Zipper’s Muscle 124″ Kit for the 107″ 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 III 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 124″ kit: * Zipper’s 4.250″ Cylinder & Piston Kit * Zipper’s Stage III 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 107, 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 heads to be provided for modification. Exchange parts may be available – Contact us for availability

In compliance with ARB emissions laws, this product is not sold or shipped to California.


Zipper’s Job Order Sheet


This product is not for sale or use on pollution controlled vehicles.

Weight 25 lbs
Emissions Compliant

Country of Origin

Engine Type

Fuel / Air



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