Don asked:
<...Could someone out there explain in detail why a richer mixture is
required when the engine's performance increases -- "hotter" cam, higher
compression ratio, better intake/exhaust -- whatever.>
Thanks,
Don Malling
Don---The folowing are my observations:
When one wants to increase an engine's performance from one that is
"stock", it is assumed that reliability, longevity and mileage are no
longer the prime considerations. Adding in more fuel and air, and
compressing it to higher numbers, becomes necessary.
The cam with higher (than stock) lift, or higher rocker ratio, lets in
more fuel and air, per stroke. Likewise the cam with a longer intake
and exhaust duration, which usually also has a higher lobe lift, to let
in (and out) more fuel and air. This type of cam also releases some of
the a/f during the overlap, esp, at low engine speeds. This then
requires more fuel to come up thru the jets (richer mix) to keep the
engine happy. This is partly due to the lower vacuum signal such cams
generate at idle and beyond.
Higher compression can more easily bring on detonation. To offset this,
a richer a/f can lower the temperature in the combustion chamber, among
other things.
A "cleaner" intake and exhaust system helps get the extra a/f mix into
and out of the engine more efficiently.
Wiout the benefit of computor contolled engine management, ths is about
the best we can do with our engines.
Dick
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