Zipper’s Muscle124” Kits from Zipper’s Performance Products have evolved from over 30 years of experience building large displacement engines, giving you pre-engineered performance kits with proven results. Designed to fit on the stock H-D® case, these Muscle engine kits provide you with incredible power, triple digit torque just off idle, and Zipper’s legendary durability. Zipper’s Muscle Kits are designed for use with high octane pump fuel.

Zipper’s Muscle 124” Kits include Zipper’s alloy 4-1/8” bore cylinders, precision-fitted with forged slipper pistons. Your heads are extensively modified with 2” intake and 1.630” exhaust valves, and then treated to full CNC porting and combustion chamber re-shaping for dramatic flow improvements using the latest machining technology. Hassle-free manual compression releases are installed for easy starting. Also Included in the kit are Pro-Taper chrome-moly pushrods, a full gasket kit, and a Darkhorse prepared S&S 4-5/8” stroke crankshaft. Zipper’s recommends a 62/64mm HPI throttlebody for Throttle by Wire applications; for cable throttle applications, a 60mm HPI throttlebody.

We’ve done the hard work for you – every part is ready to install, and the end result is more of what our reputation is made from: Big Power all the way through the RPM range!

Cylinder heads are supplied on an exchange basis. Requires case boring for the big bore cylinders and Timken® conversion on the crankcase (not included in kit price).

All kits can be purchased whole or in any combination of desired components, please contact our sales department at 410-579-2828 for more details and pricing.

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
Emissions Compliant

Engine Type


Fuel / Air


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