Since 2000 Zipper’s has been offering Best in Class CNC ported Twin Cam Heads. As the “Industry Original” we have been continuously developing new configurations for a wide variety of engine configurations to help you unlock the hidden potential of each specific engine build. Zipper’s engineering and cylinder head experts are developing new heads faster than our web master can list on the web site. Please keep this information handy as a reference guide. We will be happy to answer any questions about each cylinder head option for your engine.

In addition the engine experts at Zipper’s can provide expert advice about camshaft and custom piston compatibly with each cylinder head choice you are considering

Zipper’s CNC Ported Milwaukee-Eight® Harley Cylinder Heads

M8 Stage 2– Our Stage 2 head upgrade begins with an inspection of the seats, guides and valves. After the seat integrity inspection is completed, the valves, seats and ports are professionally machined, un-shrouded and blended to provide maximum flow in an O.E. head. This is done to achieve power and concentricity without the cost of expensive porting and oversize valve options. The Stage 2 process offers superior sealing over the OE or SE heads. Exhaust ports are machined then heads are decked and fully assembled, ready for installation. Before decking approx. cc volume 90-91 cc

• This service is available for Oil Cooled- Twin Cooled heads
• Additional guide, valve, seat replacement may be required
• Additional valve springs available for higher lift cams

M8 Stage 3- This is Zipper’s most popular fully developed CNC ported head with excellent flow that makes huge improvements to the inherently weak exhaust flow of the OE heads. Improved velocity helps make excellent early torque with stout peak HP.

For use on big bore M8 engines. O.S. Valves are + 1mm 41/33 intake and exhaust.

This head will support 150-160 HP in a variety of displacements with pump gas and exceeds O.E. or Screamin’ Eagle® results. Use with an Oversize Induction module for best results. Final combustion chamber cc range 92-93 cc.

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

 M8 Stage 3.1

Similar to the Stage 3 head, this fully developed CNC ported head has excellent flow that makes huge improvements required for large displacement M8 engines. This design has improved velocity helps make excellent early torque and peak HP.

For use on big bore M8 engines. O.S. valves sizes + 1.5mm intake 41.5/33 +1mm exhaust. Requires O.S. Induction

Final combustion chamber size range 89-90 cc

Ideal selection for use with S&S big bore kits    (is this for only S&S Big Bore kits? Is it for SE kits as well?)

• This service is available for Oil Cooled- Twin Cooled heads
• Porting performed with guides removed
• Included are Upgraded Valve Springs and new guides
• Additional valve seat replacement may be required

M8 Stage 4.0

 This is Zipper’s newest fully developed CNC ported head designed for larger output engines. This head has large increases in flow over the ST III 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

Zipper’s CNC Ported Twin Cam Harley Cylinder Heads

• Stage 1.0- The Stage I head includes a Zipper’s Performance Valve Job (Seat and guide work) , 1.850” O.S. Valves, new guides and 7mm conical springs. The head gasket surface will be skim decked to assure a true/flat sealing surface. This is a high quality upgrade to improve flow over a O.E. cylinder head.
• Stage 1.8-This fully CNC Ported head is designed for 95, 98, 103, or 107 kits. The 850” O.S. Valves, new guides and 7mm conical springs. The application allows use with OE piston with shallow valve pockets or engine builder looking for little extra low end response. The head gasket surface will be decked to assure a true/flat sealing surface. Combustion chamber volume is approximately 85-86.5 cc. *Available for Twin Cooled Heads
• Stage 2.0-This head features the same high velocity port design as the with 1.900/1.615 Valves and 7mm conical springs. Designed for use with 95, 98, 103, 107 or drop on 110 kit with aftermarket pistons. The Stage 2.0 works great with stock TB and injectors at any desired compression ratio. The combustion chambers are approx 87 cc as cast before decking. *Available for Twin Cooled Heads
• Stage 3.0- The Stage III head has larger higher flowing ports, 1.900” /1.630” valves 5/16” Step Lock Guides and dual spring that will handle up to .600” of cam lift. Full CNC chambers to unshroud the flow, ideal for higher output engines with dome pistons & larger Throttle Bodies. The Stage III  can support engines up to 130+ HP with excellent torque curves. Combustion Chambers are 91cc before decking. *Available for Twin Cooled Heads
• Stage 3.5- Stage 3.5 heads have a special high flow port design that is one of the largest we can machine into O.E. castings. Special O.S. 2.00” valves, Step Lock Guides, special valve seat machining, 5/16” dual spring for lift up to .675”. The Stage 3.5 are maximum output heads for an OE casting and are a good option to purchasing CVO castings with the added expense of porting. Combustion chambers are 92 cc as cast. *Not available for Twin Cooled Models
• Stage 4.0- The largest port we can machine into O.E castings is what you get with Stage 4. O.S. 2.00” Valves, Step Lock Guides, special valve seats, 5/16” valve springs allow up to .750” of cam lift. Max flow design for big displacement engines with large airflow demand. Stage 4.0 are maximum output heads for an OE casting. The larger valves are completely un-shrouded in the fully machined CNC cha Combustion Chambers are 98 cc before decking. *A special design part number is Available for Twin Cooled models.

CVO-MVA Castings

• CVO/MVA Stage 2.5- CNC ported designed specifically to unleash the hidden power in engines that are equipped with Screaming Eagle 117 kits with flat top pistons. The excellent flow design of the CVO/MVA Stage 2.5 is obtained with new valves, guides, springs. Custom decking is available to assure a true/flat sealing surface with added compression. This head is widely used in SE CVO 117 kits. Combustion chambers are 96 cc, additional decking optional to obtain a higher compression ratio with SE 117 kit *Available for Twin Cooled Models
• CVO/MVA Stage 3.0- This cylinder head is a work horse and is used exclusively in Zipper’s Muscle 110 and 113 engine kits. The CVO/MVA Stage 3.0 is the maximum flowing production head upgrade for CVO castings. 2.100”/1.650” valves. This head has excellent port design and dual springs for .660” of valve lift. Ideal for many max output engines. Combustion chambers are 101-102 cc before decking. *Available for Twin Cooled Heads
• CVO/MVA Stage 3.5- This cylinder head is designed for racing using CVO or MVA castings and high lift cams with larger TDC numbers to provide extra flow to meet the power needs of high output race applications. Each one is built to spec. Contact our engine experts at Zippers to discuss your specific needs. *Not Available for Twin Cooled Heads

  Evo Castings

• Ev Stage 1- These heads receive Zipper’s Stage I Performance Valve Job, 1.850” O.S. Valves, new guides and 7mm conical springs. The head gasket surface will be skim decked to assure a true/flat sealing surface. This is a high quality upgrade for a budget build! Combustion chambers are 82-83 cc before decking
• Ev Stage 2- Special high velocity port design with 1.850”/ 1.610” valves. 7mm Valves and conical springs. Designed for engines with aftermarket domed pistons. The combustion chambers are as cast and 83-84 cc before decking.
• Ev Stage 3- A special port design to promote high torque and high horsepower with 1.900”/ 1.630”. 5/16” stem Valves, Step Lock Guides and dual spring that will handle up to .630” of cam lift. Ideal for higher output engines with large dome pistons. The heads will be decked to achieve your desired compression ratio. Combustion Chambers are 85-86 cc before decking.

XL Sportster Castings   

We have multiple CNC head packages that make great power for the 5 Speed based Sportster XR 1200 and Buell engines.

Porting on 883 Castings

• Torkster Stage 2.0CNC with stock size valves 1.480”/1.355” This head is used on Zipper’s Torkster 1200 kit
• Stage 2.5- The 2.5 head has larger CNC ports and is equipped with Oversized 1.715”/1.480” valves for excellent flow. With flat top pistons, 11:1 compression or greater is easily obtainable. Makes over 100+ HP with wide torque curve on street engines. Race only applications with more compression and special valve springs are available.

04-up 1200 and Buell casting heads

• Stage 2.8- The 2.8 head for 2004-Up 1200 castings with 1.850”/1.610″ valve sizes. This head is designed for use with high performance 1200, 1250 engines.  Simple installation with many production aftermarket pistons.  Race only applications with more compression and special valve springs are available
• Stage 3- The Stage 3 for 2004 up 1200 castings using 1.900”/1.610” valve sizes. This head is popular with larger bore XL engines.  widely used on the 3.812 bore engines.  Race only applications with more compression and special valve springs are available

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If you need special springs, chamber size, compression for a competition use Please contact Zippers to discuss specific options available for your build.