Thread: Cam basics
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Old 08-06-2009, 07:02 AM   #32
GEN-IV
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Drives: 2010 LS3 / 79 Z28
Join Date: Jun 2009
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Excellent post CamaroSpike23.

Here is a little more detail on the differences between flat tappets and roller lifters. Everyone knows that roller camshafts give a more "aggressive" valve event. The aggressiveness is a function of lift, the rate of change of lift which is velocity, and the rate of change of velocity, which is acceleration. A roller cam can be ground with a more aggessive profile because it can tolerate higher stress levels and does not have the velocity limitation that a flat tappet cam has. Flat tappet cams can be ground with high accelerations, but are velocity limited due to the diameter of the lifter. Roller camshafts are not velocity limited, but the cam profile becomes concave as accelerations increase, making them expensive to grind.

Most roller camshafts are made from hardened steel, although some are made from a specific grade of cast iron, or even powdered metal. The combination of a steel cam and a quality steel roller bearing follower allow roller cams to operate at higher stress level, typically 250,000 PSI (or 250 KSI) in production engines. Flat tappet camshafts are made from cast iron, and are limited to contact stress levels of about 140 KSI.
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