In the last article I talked about what was done to my motor previously on my bike in the past. I also stated that in the process of the tear down I found that the heads were not built like they were supposed to and that has robbed my motor of power. Dave Bozzie of Bozzie Custom Performance has addressed this. The heads, though still Harley Davidson heads have been reworked considerably. They now have been ported and polished to increase the flow of air/fuel into the motor.
Porting is the changing of the size, shape, or location of the intake and exhaust ports in an internal-combustion engine. There was no reason to relocate the intake and exhaust ports but the size and shape has been dramatically changed-all in the good name of flow. Polishing, which is also being done, is just what it sounds like. Polishing the ported heads creates a smooth surface and reduces friction allowing the air/fuel to move at a faster rate.
I have always compared performance of motors to breathing; you can only exhale as much as you inhale. The name of game and the objective is to allow as much “inhale” of air and gas to enter into the combustion chamber. The more fuel in the combustion chamber, the more thorough the burn of the fuel resulting in more power.
Dave Bozzie estimates that with the heads reworked, I should see around a 10 horse power increase. We are also going to be going with oversized valves too which will make a big difference as well. Take a look at the heads in the pictures. The sooty one is the stock head…the shiny clean one has been ported and polished.
Stock valves on a twin cam motor are 1.8 inches in diameter. However, since we are going with a fairly large cam on this build they are not going to provide enough flow through the heads. We have already ported and polished the heads but now we need a larger opening to allow fuel and air to travel through. The cam we are going to install has a fairly high lift, another reason for working the heads. Due to the high lift of the cam, the stock valves have to be replaced to accommodate for the travel or lift. However, since Bozzie has removed head material and is putting in new valves, springs and guides, we are in great shape. The cam also has a pretty long duration. What this means is that the valve is going to stay open longer allowing for more fuel to enter into the heads and the combustion chamber.
The new valves are going to be 1.9 inches in diameter. This does not sound like a big difference but it really is. You could go bigger but bigger is not always better and going to a 2 inch valve would actually hinder performance. Now on a 113 or a 116 motor, 2 inch valves would be fine. Valves do get a little bigger than 2 inch but they would be useful on really big motors only.
Take a look at the valves in the pictures. You can see the subtle difference but that difference when combined with the head work equates to about 10-15 horses total.
I am pleased to say that D&D exhaust has decided to get involved in this build project. With the new components, I will need a good exhaust to ensure proper “exhaling”. The pipe I am going to go with is a Fat Cat stepped header. When it comes to performance applications, D&D is the undisputed performance leader. The Fat Cat exhaust works great on motors from stock (88 inches) to around 110 inches. Motors from 113” to 124” or bigger can benefit from D&D’s Boarzilla. I will talk much more about the exhaust in the next installment.
So, if you have any questions or comments, please contact me soon so I can address them in one of the articles. I will make sure that technical questions are answered by the true expert, Dave Bozzie. For more information on the parts, products and services talked about in the articles, check out the below websites and as always….ride safe but full throttle.
For tech questions-email Mark@outlawcommunications.com