While we're on the subject, It seems that corelating carb piston/needle
station position to engine load & speed is a major problem. How can you
know what needle stations are actually in operation under given
conditions. For example - large carbs on a small engine will never have
the pistons as far open as would be the case with smaller carbs. A carb
capable of flowing 400 cfm will not be fully open on a engine that can
only use 300 cfm. How do you know exactly what needle stations are in
play at low, midrange, & full power?
I once tried running with the hood off & a measuring stick in the top of
the damper to see what was happening under various loads. Not too
successful or accurate. It would be pretty easy to do on a chassis dyno.
In spite of gas analyzer readings, without this knowledge, we are still
completely guessing on needle profiles. Very little better than dozens
of needle trials.
I think people make assumptions that the piston is closed at idle, half
way open at some assumed midrange, & fully open at full throttle - high
rpm. Not likely in most cases. We need the equivalent of a throttle
position sensor to determine piston position.
What's the answer?
Dave Russell
BN2
Freese, Ken wrote:
> Martin,
> I read about using the oxygen sensor years ago for tuning SU's on this site.
> I thought it would be good to see if my PCV valve and the headers affect the
> mixture and the Colortune only really works at idle. I got the digital
> readout last year. Maybe I will get the oxygen sensor installed next year, a
> bung for the front three and a bung for the rear three. But for now, I need
> to fix a burned valve.
> Ken Freese
> 65 BJ8
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