Hey all this is a little long...
Based on the CR topic discussion I have some other power related issues that
I am
dealing with. Regardless of my now uncertain CR, I have a GP3 cam with a
Goodparts
Tri-carb set up that is having some mixture issues. I believe that it is
because of the
needle profile. This belief comes from soem chassis dyno time with an A/F
meter reading
the exhaust. The mixture and the power start off well but then there is a
sudden and huge
rich mixture problem that kills the power for about 1000rpm and then stays
rich all the
way to redline (@5,700rpm was as high as we went on the dyno). The A/F was
right
between 13 and 14 starting off then drops below 10 (don't know how far below
because
the scale stopped at 10) then climbs back to 11 and stays there.
The three ZS's are stock with stock needles. The testing was done at about
5,000 in
altitude (Fort Collins is 4,800 and change) which I believe to be a big part
of the
equation. Richard Good did not experience these problems but is much closer to
sea
level. The pump is still a stock mechanical and since the mixture problem is
on the rich
side I'm not worried about the pump's ability to keep up with demand although
a change
to an electric pump with a pressure regulator is in the works.
I have a comparison dyno chart between my car and a 1974 TR6 that has had the
usual
bolt on mods to a stock engine. You can view it at
http://www.loseke.net/shawn/dyno
The readings are power at the rear wheels. This is a good example of numbers
not
representing what is actually going on. The torque numbers between my car and
the 74
are fairly close. The torque curves are very different. The dyno operators
also believe that
with a different advance curve, correct valve gap and corrected mixture issues
I could get
another 15-20lbs.ft. at the rear wheels. and since HP is just a mathematical
calculation
based on torque and RPM the HP numbers would also increase.
So now the long awaited question. Does anybody have any idea of what other
needle
profiles might work better for my application? I have some ideas of how to go
about
comparing profiles but don't have the time to model them right now. I have
the Haynes
ZS book that has a selection of biased needles and the measurments for them. I
am also
ordering Kas' new book to see what he says about modifying SU needles etc...
any help would be appreciated.
shawn
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