Performance for Coast to Coast Riding
Cylinder Head Porting, Opening Up the Bottleneck in Your Engine
Cylinder heads can make or break an engine. A cylinder head must pass the air/fuel mixture into the cylinder by way of the intake valve, to be ignited by the spark plug, contain the combustion process of the air/fuel mixture, and pass the spent exhaust gases out by way of the exhaust valve and port, to your exhaust system to move the heated exhaust gases away from your precious engine. The cylinder head design of the Harley-Davidson engine has evolved in leaps and bounds in the past 30 years, from the Shovelhead era hemi style piston/head configuration, through the Evolution motor years where cylinder head flow characteristics were drastically improved, and now into the Twin Cam and V-Rod cylinder heads we have today. A cylinder head design can either be the ice cream on top of the cake, or a major concern in accessing your greatest power potential.
The reality and the limitation of the V-Twin engine is that your maximum horsepower potential is directly related to the volume of the air/fuel mixture that can efficiently flow through your engine. To attain this maximum horsepower and torque potential in your Harley-Davidson engine, the air/fuel turbulence in the combustion chamber is essential to promoting a good burn of the fuel due to better vaporization of the fuel. The process of cylinder head porting is the key to making the big bang, the big horsepower and torque numbers we are all seeking to ensure we keep you in front of the pack. It’s always a better view out in front!
Cylinder head porting is the process of reshaping the intake and exhaust post passages for improved flow characteristics. The art of cylinder head porting is a skill possessed by few, and sought by many. The success and failure of cylinder head porting work is measured on a calibrated flow bench, and the flow results are measured in cubic feet per minute (CFM). Porting is not to be done by a novice. Modifying a port for improved flow is a delicate balance of flow velocity and volume. The flow velocity must be as high as possible for responsive torque in the low to mid RPM range, while the flow volume must be sufficient to supply the engine with all the air/fuel mixture it needs to reach the maximum high RPM range power. Having the increased flow volume while maintaining a high velocity across the RPM range to redline is the trick that results in a broad powerband, yes, having that power there when you want it.
The issue of port polishing has been going on for years. Some say that fully polished ports offer the least resistance to the flow of the air/fuel mixture and exhaust gases. While others say that polishing the intake port to a satin like finish, and the exhaust port to a full mirror like finish is the best method. The satin intake with polished exhaust port is preferred by many of the top cylinder head professionals. A side benefit of the mirror like finish is a greater resistance to carbon deposits forming in the port. The truth of all this, is that the contour of the port is more important to flow than a mirror like finish.
Before you go spending any money, remember that your ported cylinder heads won’t perform to their maximum potential if they are not coupled with compatible camshafts, pistons with the dome shape and the right compression ratio, the right size carburetor/EFI injector body and injectors, a strong ignition system to ignite the mixture, and an efficient exhaust system to move the spent gases out. Calgary Harley-Davidson/Buell® has taken the time to come up with proven engine packages that will work for your Touring bike, or for your lighter weight Softail or Dyna series bike. A good engine package is a lot like baking a cake. With the right ingredients, assembled properly, you get something that is appreciated and enjoyed. If you try mixing unproven combinations of engine parts, it can be a hit, or a real miss.
