Zipper’s Muscle 98” Kit for ’99-’06 Twin Cam® 88” engines boost torque and horsepower north of 110! The Muscle 98 gets its displacement boost by increasing the cylinder bore size to 3.937” when paired with the factory stock 4” stroke crankshaft. Your cylinder tops are decked for trueness and new 10.5:1 forged pistons are precision-fit using the latest Sunnen equipment, while your heads receive Zipper’s high-breathing Stage III treatment with CNC porting, new guides, oversize valves, performance springs and manual compression releases. Zipper’s Red Shift 577 cams provide big torque & HP gains across the entire RPM range. Also included are Pro-Taper pushrods and EZ-Adjust covers, with all gaskets needed for assembly. Highly recommended option: Zipper’s # 417-495 blueprinted cam chest upgrade with our patented Red Shift Dual Piston hydraulic cam chain tensioners, blueprinted billet plate, HV oil pump, cam bearings and quality USA lifters for improved reliability and durability. The Muscle 98” kit produces 33% more Horsepower and 10% more Torque than a factory-stock 107” M8!

This kit uses your factory head & cylinder cores sent in for modification.  An exchange may be possible once your cores are cleaned, inspected and qualified for exchange.


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

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