Owners of Evolution® powered Big Twins can increase their engine’s output with a set of our CNC-ported EV heads! The factory casting is CNC-machined to our proven high torque, high power port shapes and the valve sizes are increased to 1.900” intake and 1.630” exhaust. Ductile iron Step-Lock guides are fitted and topped off with high quality Viton® seals and a performance spring kit. The head gasket surface is decked for flatness and your cam/compression requirements before final assembly.

• Full CNC intake & exhaust port machining
• Ductile iron step-lock valve guides
• Competition seat work on Serdi equipment
• 1.900” Int, 1.630” Exhaust stainless steel valves
• Performance valve springs with Moly collars
• .630” valve spring free travel
• 91cc combustion chamber (skim decked)
• Completely assembled, ready to install

This head has substantially higher low-lift flows for unreal torque increases and is capable of producing over 90 horsepower in an 80” engine (same head used in our 80/80 kit). Requires use of pop-up pistons and possibly additional deck machining for proper compression, depending on your choice of cam and pistons. Spring travel is set for up to .575” valve lift; higher lifts will require an optional spring change.

Evolution® CNC headwork is performed on supplied head cores; in-house shop time is 5-10 working days.

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. A small cleaning charge applies to heads sent in for modification.



Zipper’s Engine & Powertrain Service Request Form


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 1 lbs

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