The new Zipper’s MUSCLE 128″ – STAGE 4 Engine Kit is the latest and most powerful top end kit we’ve ever produced for this displacement on a production motorcycle!

The Stage 4 Muscle 128 kits are extensively track tested at Zipper’s R&D for power and durability.

Zipper’s Exclusive Stage 4 CNC heads with +2mm Oversize Stainless Valves are built with extraordinary attention to detail, by skilled craftsman to assure maximum flow and durability.

Each Kit is supplied with our 4.250″ Alloy drop-on cylinder with thermal coated forged pistons. Cylinders are precision sized by a Zipper’s craftsman using the latest honing technology on a Sunnen SV-30, and then the rings are hand fitted to each bore.

Red Shift RS588 cam is specifically designed to deliver an outstanding Torque and HP curve to provide instant acceleration from any RPM.

Click here to view Red Shift M8 Cams

Stage 4 Muscle Kit Highlights

  • Cylinder Heads- Zipper’s CNC Stage 4 with + 2.0 mm oversize valves
  • Special Thermal Coated Forged 4.250 Pistons
  • Camshaft- Red Shift 588
  • Power Ratings- 150+ ft-lbs Torque and 165+ Peak HP
  • Smooth Power with Excellent Torque from off idle to peak power
  • Excellent Throttle Response and Drivability
  • Works with Specific Production Exhaust Systems
  • Designed for use with Pump Gasoline

Requires your heads to be provided for modification. Exchange parts may be available – Contact us for availability

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


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.

Weight 1 lbs

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