This is at rpm when the engine is said to be 'off the cam'. In other words
the engine needs lots of overlap at high rpm to get all the mixture in it
needs but at low rpm the gas flow through the engine is much slower and some
of the inlet charge simply wafts out of the exhaust tract.
In a message dated 09/01/02 15:04:20 Pacific Standard Time,
> . However even in a finely tuned engine, some unburned fuel exits
> during the exhaust stroke because the intake valve begins to open before the
> exhaust valve is fully closed. This is known as valve overlap. The more
> radical a cam, usually the more valve overlap, and the greater amount of
> unburned fuel dumped unused out the exhaust pipe.
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