A/R Ratio, are these numbers ok?

[Vipergrün]

Should have read "A/F" ratio....

Ok, so I have read that an A/F ratio of 12.5 will probably yeild the best performance. According to my PLX A/F meter, I have idle set to 15.5-16.0 and at WOT I dip to 11.6 or so. General cruising yields around 13.5 - 14.0. How do these numbers look? This is with CIS not using Lambda. I still do not know CIS that well, but can I keep the idle where it is but lean out WOT a bit? Or is there just the one setting at the fuel distributor?

Thanks
-Brad

[kuehl]

How do the plugs look?

[jpahemi]

Brad:
Where did you get the 12.5 figure? Is this an average # for all engines, or specific to the 911?
j.p.

[steand]

The figures seem a lot like mine 79' SC, where i have a wideband Lambda sensor to measure A/F. The CIS system is not that precise about A/F ration above all running conditions. when my engine is cold the A/F ration is also a bit lean on Idle, and that shows up as a lower RPM on cold idle (say 700-800rpm), and as the engine warms up the WUR/FPR (warm up regulator/fuel pressure regulator) richens the mixture to about 13.5, and my idle goes up to 1100.
Everytime the Throttle is blipped (pressed) the vaccum lines to the FPR richens the A/F, like an accelerator pump on a carburettor. Mine goes to A/F around 11.

[Vipergrün]

Originally posted by jpahemi
Brad:
Where did you get the 12.5 figure? Is this an average # for all engines, or specific to the 911?
j.p.

It's kind of a generic number from reading various info. Not hard and fast. It seems that A/F of 12-12.5 for turbos and 12.5-13 for NA motors.

It has also been suggested that if we are running at 11-11.5 at WOT, we are leaving power on the table. From what I understand, CIS is using the frequency valve at WOT, so that may be a place to look. I plan on diving into this a bit further.....when I have time.

[kuehl]

fYI

on our 87 3.2, our wide band on start up (cold start)
starts off at 12.0 nominal and then walks up (leans out)
to 14.5-15.0 nominal after she is warm; id say the average
after warm up is 14.7

normal idle up to WOT is always 14.5-15.0 nominal, and you can watch the movement (between 14-15) as the DME does its job.

On WOT she's 12-13 nominal.

we say "nominal" because we are using a 2 decimal place display and there is always a range or tolerance.

[kuehl]

fYI

on our 87 3.2, our wide band on start up (cold start)
starts off at 12.0 nominal and then walks up (leans out)
to 14.5-15.0 nominal after she is warm; id say the average
after warm up is 14.7

normal idle up to WOT is always 14.5-15.0 nominal, and you can watch the movement (between 14-15) as the DME does its job.

On WOT she's 12-13 nominal.

we say "nominal" because we are using a 2 decimal place display and there is always a range or tolerance.

below 14 keeps things cool whereas near 15 may yield
better mpg and some nominal power

[sammyg2]

Just to add, my 1980 sc did almost exactly the same thing before I got the lambda brain functioning correctly.
I still haven't figured out of it is supposed to be like that or if it is something that is malfunctioning. I've asked that question before but didn't get a difinitive answer.

I had the idle set as lean as I could get it and still have it run (around 16 to one) and when it went to part throttle cruising it went rich to 13.5 to one. Full throttle was rich like Brad's. As soon as I let off the throttle it would gurgle out the exhaust like little backfires and go really lean at 17 to one.
My solution was to get the lambda sensor and brain working right and that took care of it but it still feels like a band-aid to the problem instead of the solution.
I really wish I knew for certain if this type of behavior is by design or caused by a bad component, and if so which one?