The 4-valve M8 cylinder head flows considerably more air than previous 2-valve heads – but it needs to, to support today’s larger engines. Flow testing the stock heads shows an imbalance between intake and exhaust flow ratios.

Our STAGE 2 head upgrade begins with a disassembly and inspection of the seats and valves. After the seat integrity inspection, factory guides are removed and replaced with long wearing manganese bronze guides and fitted with precision care.  The valves and seats are professionally multi-angle machined and port blended to provide maximum flow in an un-ported head to achieve power and concentricity without the cost of ported heads. This process offers superior flow and sealing over the OE or a SE head. Heads are decked and fully assembled, ready for installation. Before decking, approximate cc volume is 89-90 cc.

• This service is available for Oil Cooled- Twin Cooled heads
• Additional valve or seat replacement may be required-quoted after inspection
• Optional upgraded valve springs available for larger lift cams

  • 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.

Zipper’s Performance Part Number:  517-852EX

*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.

Weight 20 lbs
Dimensions 10 × 10 × 10 in

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