Tech Tip - Air Flow

Do you want more power from your Harley-Davidson engine?

Increased air velocity is one of the primary keys to excellent street performance. The difference between a set of heads with over-sized ports and in-take valves versus raised port heads with stock valves may not always show up as a difference in maximum horsepower (all other components being the same).

Both engines may produce the same maximum HP, but the raised, D-shaped port heads will produce much more torque resulting in the maximum horsepower output to occur at a lower RPM. The lower RPM range of the engine makes it more potent on the street - grab a handful of throttle and the bike will pull like a freight train, no more waiting for the engine to "come on the cam"... You’ll be guaranteed to beat your friends on the stop light Grand Prix circuit.

The key to a cylinder head design producing high horsepower is in creating high velocity air flow through the ports. This is easier to do with smaller ports rather than large ones. High velocity does a couple of things that are very positive to making power.

    1.The higher the air flow speed, the better the air/fuel mixture is atomized as it passes through the carburetor/induction module. This improves the combustion process.
    2.The higher velocity improves the combustion chamber 'swirl'. The 'swirl' distributes the air/fuel mixture in the combustion chamber, improving the combustion process.
    3.The higher the velocity, the greater the inertia of the air flow. This helps fill the cylinder to its maximum, improving the 'volumetric efficiency'. High velocity engine port designs can achieve volumetric efficiencies of almost 100% in certain RPM ranges, meaning you just put 5 1/4 pounds in a 5 pound sack. This is very good for producing high horsepower.
    4.Smaller ports work better at low RPMs. If you are riding a street bike, most of you time is spent below 3000 RPM. Why have a port designed for 6500 RPMs?

Harley-Davidson has designed and produced many different styles of heads for all of your racing, playing or touring needs. So when building an engine talk to one of our experts to pick the right combination for you.

Tony D. & the Service team at Wild Fire H-D