How to choose a camshaft
From Crankshaft Coalition Wiki
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==Overview== | ==Overview== | ||
The camshaft can be thought of as the brain of the engine, and it has a very large effect on the amount of power an engine makes as well as where in the rpm range that power occurs. The main focus of this article will be on a conventional OHV (overhead valve), cam-in-block engine configuration using two valves per cylinder, as shown above. | The camshaft can be thought of as the brain of the engine, and it has a very large effect on the amount of power an engine makes as well as where in the rpm range that power occurs. The main focus of this article will be on a conventional OHV (overhead valve), cam-in-block engine configuration using two valves per cylinder, as shown above. | ||
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====Narrower LSA:==== | ====Narrower LSA:==== | ||
| − | A narrower LSA will ''increase'' overlap. This has a tendency to | + | A narrower LSA will ''increase'' overlap. This has a tendency to increase engine output at lower RPM and decrease engine output at higher RPM. A narrower LSA tend to make less peak power but more average power. |
| − | *Moves torque to | + | *Moves torque to lower RPM |
*Increases maximum torque | *Increases maximum torque | ||
*Narrow power band | *Narrow power band | ||
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====Wider LSA:==== | ====Wider LSA:==== | ||
A wider LSA tend to make less peak power, but a broader powerband. Changing the LSA also changes the valve timing events; opening the exhaust valve sooner and closing the intake valve later, both of which affect how the engine ingests air. | A wider LSA tend to make less peak power, but a broader powerband. Changing the LSA also changes the valve timing events; opening the exhaust valve sooner and closing the intake valve later, both of which affect how the engine ingests air. | ||
| − | *Raise torque to | + | *Raise torque to higher RPM |
*Reduces maximum torque | *Reduces maximum torque | ||
*Broadens power band | *Broadens power band | ||
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===Lobe intensity=== | ===Lobe intensity=== | ||
| − | One more point about the cam profile is lobe intensity. For a given duration, more lift means the lobe ramps (the opening and closing faces on the sides of the lobe) are steeper (more intensity). That is to say, the cam lobe | + | One more point about the cam profile is lobe intensity. For a given duration, more lift means the lobe ramps (the opening and closing faces on the sides of the lobe) are steeper (more intensity). That is to say, the cam lobe has to accelerate the lifter faster to get to the peak lift within the available amount of duration duration. Faster ramp speed can give more "area under the curve", which usually equates to a broader, less peaky powerband. The downside for flat tappet cams is that the steeper ramps mean they contact the lifter at a greater angle, so the potential for wiping out a cam lobe or lifter is greater. Manufacturers are well aware of this, so they try to design the lobe profiles to optimize power, yet maintain good durability. Cam profiles like the Comp Cams XE-series and Lunati's Voodoo line are both at the edge of how fast the valve can be safely opened and closed. That's why they caution against using a higher ratio rocker arm when using these grinds. More on lobe intensity can be seen [http://www.harveycrane.com/duration.htm '''at this page'''] by Harvey Crane of Crane Cams. |
===Intake centerline (ICL)=== | ===Intake centerline (ICL)=== | ||
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===Crankshaft Coalition wiki articles=== | ===Crankshaft Coalition wiki articles=== | ||
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