Camshaft duration is one of the major keys in producing torque and throttle response in your engine. The duration of the cam at 0.050" tappet lift is the key. Many cam grinders take different approaches to measuring advertised duration figures. The best bet is to compare the grinds at 0.050," and then begin to assess the other features of the cam. Cam lift is important too. In today's camshaft arena, the trend is to lift the valve quicker and higher, then settle the lifter down gently.

While on the topic of long duration figures, it is not completely impossible to make a long duration cam work -- especially in an application that might see limited street use. In order to make use of long duration figures in certain combinations, the camshaft overlap can be decreased. This is made possible by increasing the camshaft lobe center (remember, this can only be done during cam construction). Spreading the camshaft lobe centers actually decreases overlap measurably and you might be able to use more duration that you had thought possible. Spreading the lobe centers does influence idle and part throttle driveability by a significant amount in some applications, but it does come with other added "costs". These "costs" include a reduction in top end breathing capability. With the lobe centers spread apart, overlap decreases and the engine loses a portion of its scavenging ability. In simple terms, the engine runs out of breath on the top end, but throttle response, mid range power and idle quality are retained.

When camshaft lobe centers are reduced, the engine tends to become peaky in power output, but there's a caveat here too. If the engine has a long stroke, and small intake port (volume), high flow heads, then there's a good chance the "peakiness" is a moot point. An engine that is "peaky" simply means that it will develop good power at a specific rpm range, but will become quite lazy in another. This is where the overlap question re-enters the picture. A combination of tight lobe center angles and long duration numbers produces a relatively large overlap figure. As a result, the power band is tightened. Certain road race applications respond favorably to this type of camshaft, but keep in mind that road racing almost always involves gearing the vehicle (transmission and rear axle ratios) to the specific racetrack. High rpm, stick shift, lightweight drag race cars can also make use of this type of camshaft, but even in the specialized worlds of racing, the applications are quite limited.

Stay Tuned! Part 2 of "CAM-ROD-ERY" coming soon!

 

Special thanks to Crane Cams for the preparation of this article. Crane Cams can be reached at:

Crane Cams 530 Fentress Boulevard Daytona Beach, FL 32114 PH# 904-258-6174 Fax# 904-258-6167