Bishop's Performance - Home of "HammerHeads"

For maximum performance, there is no doubt that optimizing the ports in the heads and manifold is critical. The best cams, pistons, exhaust, carburetors, and air cleaners in the world won't give you maximum performance if the heads won't flow the air. Air = Power
If you have a Twin Cam, head porting is almost a necessity! Did you know that the early Twin Cam heads flow less air than Evo heads, even though they have to feed a larger displacement engine? With proper porting, stock heads can outperform many "performance" heads, yet you maintain a stock appearance.

"HammerHeads" Head Porting Twin Cam, Evo, XL, Thunderstorm
Stage 1 =	^{^$}400	Full Porting; Stock Guides, Valves, & Springs
Stage 1 =	^{^$}440	Full Porting, Hi-flow Valve Guides, Stock Valves & Springs
Stage 2 = for low-lift cams	^{^$}620	Full Porting, Stock Valve Springs, Hi-flow Valve Guides, Oversized Hi-Flow Intake Valves, Stock Exhaust Valves
Stage 2 = ('04 - earlier).	^{^$}715	Full Porting, Hi-Performance Valve Springs & Valve Guides, Oversized Hi-Flow Intake Valves, Stock Exhaust Valves
Stage 2 = ('05 - later TC)	^{^$}725	Full Porting, Hi-Performance Valve Springs & Valve Guides, Oversized Hi-Flow Intake Valves, Stock Exhaust Valves
Stage 2 = ('05 - later TC)	^{^$}760	Full Porting, Hi-Performance Valve Springs & Valve Guides, Oversized Hi-Flow Intake & Exhaust Valves (retrofit to all pre-'05 valves, guides, & springs)
Stage 3 =	^{^$}975	Full Porting, Hi-Performance Valve Springs & Valve Guides, 2.00" Hi-Flow Intake Valves & Seats, 1.615" Exhaust Valves
Work Order Form Please print this form and enclose it with your parts
Average return time is approximately 2 weeks. Prices do not include shipping. All stages include carburetor manifold porting and new valve guide seals. Fuel injected? Check out our throttle body modifications here.

Looking to buy some heads for your Harley?
We have a few used sets available for sale, without exchange, on the Garage Sale page.

Hammer's head porting technique....

One of the bottlenecks of the HD ports is the short side radius. The air wants to take the shortest path and that is the floor of the port. It also doesn't like to make sharp turns. To address both of these issues, I flatten the floor some which creates more area and I smooth out the radius leading to the valve and the combustion chamber allowing more air flow in the area that is restrictive. I also reduce and reshape the boss extending into the port around the valve guide which helps the air flow separate and flow more cleanly around the valve guide. The bowl area transitioning to the valve seat is reshaped to optimize flow from the valve guide area to the valve.
For Stage 2, the seats are opened up for the larger 1.90" valves and blended to the bowl and the combustion chamber. This along with a three angle seat promotes excellent air flow between the valve and the seat. The whole port is given a specific directional texture finish that will help prevent the fuel from separating out of the air stream and promotes better atomization of the fuel. Liquid fuel doesn't burn, the vapors do. The more the fuel is vaporized the more efficiently it will burn producing more power with less fuel and the less chance of detonation. The valves I like to use have a 28° radius on the back side of the valve to help the air flow around the head of the valve and into the combustion chamber. I don't enlarge the port so much that velocity is reduced to a level where low end power and drivability are sacrificed.
In the combustion chamber, I smooth and lightly polish the walls after blending. The smooth transition from the seat to the chamber helps increase low lift flow and the polishing helps prevent carbon build up. I don't try to mirror polish because it really does nothing for performance and is very time consuming. I can mill heads to accommodate any desired compression ratio.
The exhaust ports on Twin Cam heads are very restrictive and need a lot of attention. The exhaust valve size is not the problem with these heads so I retain the stock valves. I do a lot of the same work to the exhaust port as the intake. The difference is the exhaust port gets enlarged in the area that has been reduced so much and I smooth it like the combustion chamber. The smoother surface actually has less surface area and will absorb less heat. Less heat absorbed by the head in the combustion chamber means more heat in the combustion process and more pressure on the top of the piston. Less heat absorbed by the exhaust port means hotter exhaust gasses and higher exhaust gas velocity.
In pre-'05 heads, the valve guides I use are a design of my own I came up with after years of studying the valve guides in every head I've been able to get my hands on. I use Rowe stock style guides and shorten them and retaper them on the lathe. They utilize OEM style valve stem seals or any direct replacement seals. Optional with Stage 1, and included with Stage 2, are new high-performance valve springs. '05 and later heads can be retrofit to the earlier parts if needed, or we can work with the stock-style performance components.
The price for my heads always includes porting your carburetor intake manifold. The manifold is an extension of the intake port and should not be overlooked. A lot of flow gain can be had in the manifold. I reshape the short side of the manifold similar to the ports and give it the same directional textured finish as the intake port. I have found that these methods of modification produce great performance and efficiency. For fuel injected bikes, the throttle bodies should also be improved for maximum performance.
Just as every person is different, so is every build. I always like to talk with people to find out what type of performance they are looking for, and what is their style of riding. Only then can I help them determine what parts may work best to get them where they want to be, and I make sure that my head porting is always matched to the whole package. If anyone has any other questions feel free to call or email me. I can help with any kind of build and I'm happy to answer any questions the best that I can.
- Hammer

Horsepower is an illusorymathematical equation. Torque is realand the source of allgood things in the world.

Head Porting

Horsepower
is an illusory
mathematical equation.
Torque is real
and the source of all
good things in the world.