Put a set of our Stage III ThunderSport heads on your Sportster® to really let it breathe! Each port is fully CNC machined for exceptional flow rates; two available combustion chamber sizes are un-shrouded and CNC machined for accuracy in volume. Step-Lock guides are installed and honed to precise size, and seats are radius machined to our proprietary shapes on Serdi equipment for oversized valves of 1.900” and 1.615” diameter (883 heads have all 4 seats replaced to accommodate the larger valves). Viton seals and our Pro-Street springs with Titanium collars are installed to provide proper valve train control. These ThunderSport heads will allow your Sportster® engine to reach its full potential!

    • Full CNC port & combustion chamber machining
    • Ductile iron step-lock valve guides with Viton seals
    • Competition seat work on Serdi equipment
    • 1.900” Intake, 1.615” Exhaust stainless steel valves
    • Performance valve springs with titanium collars
    • Completely assembled, ready to install

Work is performed on your supplied head cores; shop time is approximately 5-7 business days (allow for additional time during peak season).

International Customers – Import duties are not required when shipping your castings for modification. Special low shipping rates are available for your cores; contact your sales representative for details.

Supply us with your piston volume and camshaft for final cc volume through decking.

Remove heads from engine, wash off oil and ship to Zipper’s as-is. Improper cleaning methods can actually do more harm than good; we suggest you allow us to properly prepare your heads for modification. Extreme care is taken during our preparation process to preserve component finishes. A small cleaning charge applies to heads sent in for modification.

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.

Click here for Zipper’s Job Order Sheet

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