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jluetjen jluetjen is offline
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Join Date: Oct 2001
Location: Westford, MA USA
Posts: 8,592
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Reversion????

With the throttles (mostly) closed you could be running some degree of vacuum between the butterflies and the intake valve during overlap, while the exhaust (especially if in a specific range of it's "tune") may be seeing positive or ambiant pressure. The result is that exhaust is pulled back into the cylinder or even up into the exhaust. Once you open the throttles, the vacuum goes away. 500 RPM on either side and the exhaust will have a negative pulse at the exhaust valve and the engine feels fine. Once the RPM's pick up, the exhaust develops enough inertia to pull the charge into the cylinders right up to peak HP rpm.

I could picture increasing the CR will increase the amplitude of the exhaust pulse, so the vacuum pulses get stronger, but so do the pressure pulses between them.
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John
'69 911E

"It's a poor craftsman who blames their tools" -- Unknown
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Old 05-19-2005, 05:51 PM
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