Thread: Lobe Center
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Old 12-18-2002, 02:15 PM
Excaliber Excaliber is offline
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360 degress in a circle. Less degress, smaller circle, more valve overlap (as I too am used to calling it). 180 degrees would be two lobes directly opposite each other, no over lap would be possible at all!

108 would open 4 degrees of rotation sooner than 112. At low rpm and 108 degrees the exhaust would tend to blow back up into the just opening intake valve port. "Flow" would be erratic and disturbed (like me). A rough idle would result.

As rpm increases' the "inertia" of the exhausting and entering gas flows would tend to keep them smooth and flowing in a constant direction. The exhausting gas velocity would actually help "pull in" the fresh intake charge, thus effieciency would be dramatically improved. NO overlap means NO help with one flow complementing the other.

Header\tube\muffler length would play a key role in maintaining this effect. Good cam profile but with a bad header setup, won't be as "effecient".

I'm "guessing" a motor built for torque, low rpm, will have little or no over lap, but what "number" is that? Gas flows at low rpm would not be fast enough to create the "inertial" effect. High rpm with very fast "gas flows" would be able to take advantage of a LOT of over lap. But if your cam "comes in" at 5000 rpm and the intake manifold works best at 4800 rpm and the headers like 6000,,,,you see the problem?

Ernie

Last edited by Excaliber; 12-18-2002 at 02:22 PM..
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