Harley Davidson Cams, What You Need to Know to Modify Yours

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cam.jpgHarley-Davidson cams can be modified to increase air flow and improve induction and exhaust cycles. Cams also have a major impact on the engine and control what goes on during operation. By modifying the cams, you can make changes to the engine’s horsepower and torque curve. It is important that all components match the engine’s application. There are many things to consider before you begin modification.

Choosing a Cam

Choose a cam that will increase rpms where you need it, either on the higher or lower range. Decide if your main goal is to increase horsepower or torque. Gather information about your bike concerning engine displacement, exhaust airflow, rod length, and even the weight of the bike. Heavier bikes need more power in the lower rpms to get it going. Lighter bikes can handle longer duration in the cams because it has easier acceleration. It is important that your new cam is the right size for your bike, not too big or small. Match the cam to your engine’s duration, lift, overlap, and timing as closely as possible. These are some of the determining factors for choosing your Harley Davidson cams.  

Understanding Cams

The lobe on the camshaft is designed to open and close the valves. The shape of the lobe is an important determinate of when and how the valves open, and how quickly it happens. There are several different types of engines, each with their own number of cams, valves, and lobes. In pushrod engines, the cams are located near the crankshaft, while the popular V-rod engine has overhead cams. The opening and closing of the valves and duration of the cams play an important role in increasing performance. Duration of the valves can be figured using a simple formula which adds together opening and closing numbers with 180 degrees of the crank’s movement. Increased duration will increase horsepower, but decrease torque.

Other Factors

Lift is another factor to consider when modifying your Harley-Davidson cams. You can get more power by increasing lift, but an increase in duration may also be necessary to flatten out high acceleration rates which can adversely affect your bike. You can determine lift by considering the cylinder head design and the valve’s diameter. Overlap is another factor that can affect fuel intake and exhaust performance; it must be tuned correctly so that it performs at the right rpm. The lobe centerline and separation angle are important and affect overlap. The bigger your engine’s displacement and higher rpms, the more overlap you will need for maximum performance. Often changing the valve’s timing can cause the cams to open and close more efficiently, and increase engine power. Figure correct compression ratios to maximize low rpm performance. An engine with a higher rate of compression may work better with valves that open earlier. In lower compression engines, delayed valve openings may be beneficial.

(Click here for a helpful step-by-step cam swap at HDForums.com!)

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