Douglas Shook wrote:
>Hi Harold,
>
>
>Again, I am not disagreeing with you one bit, but even
>using the same scales, the TR6 engine lost 1/3 of its
>bhp from the PI version to the '72 USA version trying
>to cope with the emissions issues.
>
Doug,
While I can't offer any specific information, I can only suggest a
bit of in-
formation- that camshafts are very critical in determining power and
emission
characteristics. The primary concern here is "overlap". This denotes
the length
of time, measured in degrees, that both the exhaust and intake valves
are open.
You may wonder why anyone would want both valves open simultaneously,
but the answer is rather complicated- it has to do with the exhaust
creating a
"suction" that helps draw the intake charge into the cylinder. The downside
to this is that some intake charge also escapes out the exhaust,
creating a high HC
reading (HydroCarbons are unburnt fuel).
From what I can gather, higher lift on a cam shaft does not create any
adverse
emissions problems, but since there is a certain ratio of lift to
duration that
is deemed advisable for long lobe/lifter life, any signifigant increase
in lift will
be accompanied by a resultant increase in duration, there is a limit to
what can
be "improved" upon and still meet a set emission standard.
The morale is: When dealing with camshafts, watch out for long
durations, and
look for an increase in lift when trying to keep HC emissions down.
Joe IV
TR 250
P.S. Ignition timing is also very important in relations to emissions,
but I am unable
to offer any insight on that topic.
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