Race Motor/porting Questions
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From: n
Originally posted by Hamza734
Pumping dynamics are in play at all engine speeds. As you correctly pointed out, the effects are reduced at higher RPM's. However, each rotor turns at 1/3 engine speed. Consequently, even at 9000 RPM's the rotor is only turning at 3K. At these speeds, pumping dynamics are still critical....
Pumping dynamics are in play at all engine speeds. As you correctly pointed out, the effects are reduced at higher RPM's. However, each rotor turns at 1/3 engine speed. Consequently, even at 9000 RPM's the rotor is only turning at 3K. At these speeds, pumping dynamics are still critical....
Computing the absolute dynamics of the intake charge vs the exhaust WOULD be damn near impossible. However, one can still quantitavely say overlap matters. Why? Because the driving force to suck in the intake charge is vacuum. The longer the exhaust stroke continues into the intake stroke, the greater the vacuum. Given ports of equal size, the one with the greater vacuum (the one with the most overlap) will suck in the most intake charge. It'll also be the most efficient, as pumping losses will be less.
In a sense the point is moot for rotaries. Since all but the mildest porting increases overlap it'll be impossible to consider whether overlap is responsible or port size. I would argue both, with port size being a bit more important.
My porting has evolved to no increase overlap from the stock ports.  All I do in basically increase duration, especially on the intake.  Increasing duration on the exhaust hurts torque, as I found out with my car - 253.9hp and 207lb-ft - but that was expected.  I would love to do a back-to-back comparison with no overlap increase versus mild overlap increase, but this entails a rebuild in between!  I currently don't have the resources to pull this off right now...
-Ted
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From: midwest
Yeah, I guess the question is how much of an effect does this contribute to the power output...
My porting has evolved to no increase overlap from the stock ports.
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From: n
It's a compromise situation.  The non-bridge primary tries to keep the intake velocity high while the bridged secondaries give you the added flow.  I usually want it full on or nothing - so I would go full bridge. 
Idea on what my intake port would look like - here's a recent template I made.  Notice the stock port underneath...
-Ted
Idea on what my intake port would look like - here's a recent template I made.  Notice the stock port underneath...
-Ted
Senior Member
Joined: Jul 2002
Posts: 625
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From: midwest
It's a compromise situation. The non-bridge primary tries to keep the intake velocity high while the bridged secondaries give you the added flow. I usually want it full on or nothing - so I would go full bridge.
-Hakan
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