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Re: Needle position was: haystack Was: Oxygen Sensors

To: "Freese, Ken" <Ken.Freese@Aerojet.com>
Subject: Re: Needle position was: haystack Was: Oxygen Sensors
From: Dave & Marlene <rusd@velocitus.net>
Date: Thu, 24 Jun 2004 09:59:49 -0600
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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