Zipper’s STAGE 4 – ThunderSport CNC Headwork for Milwaukee-Eight® Engines

This is Zipper’s newest fully developed CNC ported head designed for larger output engines. This head has large increases in flow over the STAGE 3 and tightens the spread between Intake to Exhaust flow ratio with significant improvements to the exhaust port design.

Only for use on big bore M8 engines. O.S. Valves are + 2mm 42/34 intake / exhaust valves.  Requires oversized Induction. Final combustion chamber cc range 89-90 cc.

• This service is available for Oil Cooled- Twin Cooled heads
• Porting performed with guides removed
• Included are Upgraded Valve Springs and New Guides
• Oversize valve seat replacement is required with 4.0

Work is performed on your supplied head cores. Once heads are received at Zipper’s, Shop Time is approximately 15 business days (during peak season allow for additional time). Exchange heads may be available if the condition of your cores qualifies. Currently we do not offer M8 cores for sale. Please send your cores in for processing or exchange.

• Processing time

Once the cores arrive at Zipper’s they are unboxed, and inspected for shipping damage. Then we review your job order sheet and other related documentation. Job sheets that have not been finalized before your cores arrived will take additional time to sort thru before the job is put into production. Once finalized, the cores will be disassembled, serialized then move into production. Turn around (Process time) varies depending on the time of the season and how long it takes to get your job sheet finalized. Because of the dedicated skilled labor at Zippers and the vast amount of capital equipment we get the work completed with the highest standard of quality with one of the best turnaround time in the industry.

Work is performed on your supplied head cores.

For our standard production heads Shop Time is approximately 15 business days (during peak season allow for additional time).  The below options will require additional time to process:

• • Custom Modifications
  • Custom Finishes
  • Require Thermal coatings
  • Needing Additional Repairs
  • Or other Non-Standard Work

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.

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.

*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

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.