Who with CIS is running an AFR gauge?

[rwest]

Hi,

While setting up my EFI, I was thinking that the AFRs that CIS runs during cruising would be useful to know.

So my question/favor is could you tell me what AFR you see while just cruising along at 30, 45 and 60mph or so on your CIS car.

Thanks for any input,
Rutager

[PeteKz]

Rutager: Be careful what you ask for...

A number of us have AFR gauges on our CIS cars. I do, Icarp does, OldH2S does, etc. In my experience, and those with whom I've compared notes, the AFR is all over the place. You would think that the WUR should make the AFR go lean under cruising and off throttle conditions, and go rich when you put your foot down, but it usually seems to do the opposite! This has led several to install manual pressure valves to replace the WUR. I'm considering the same, except that I understand there is an electronic version soon to be available that will do what the WUR is supposed to do, but more reliably and adjustably.

Why are you asking?

[rwest]

Hi Pete,

I was curious to see what kind of AFR a 911 motor was happy with just tooling around. I know when I had CIS, I would get 26mpg on long road trips, so I was trying to get a baseline AFR to aim for in cruising that the engine was happy with and delivered decent mileage.

Thanks,
Rutager

[icarp]

Icarp here, at 80 mph I run my adjustable reg at x psi to achieve 28 mpg @ 15.2 afr

The x psi is to not put a reference # , I have cams and an adjustable WUR in my cockpit .

Start psi 30* cold is 17 psi, 80* is 27 psi driving is 29.5 to 31 psi control pressure .
This is according to my gauge . stomp on it AFR is 12.8-14.0

works like a charm

Ian

[eastbay]

I have one on my current 74 2.7 with CIS, not stock.
(JE pop ups-964 cams-ported heads by CGarr, etc)

I have mixture set to: idles mid to high 13s

will see 14-16s on very light throttle cruising
mid to low 13s on medium throttle
drops into the 12s on heavy throttle

The AFR gauge says it is good to .5 of AFR and I think it reads leaner than it is.
(mileage stinks)

I tried to buy a PMO EFI system right when they were sold, Richard called me and said 'sorry, can't fill your order'

I follow your thread with interest as I will go EFI sometime in the future.

[Hi_Fi_Guy]

Did anyone see the episode of Wheeler Dealers where they installed “modern EFI’” on a CIS Audi Coupe but retained the CIS air meter with some sensors added? Made me wonder if any 911 SC owners had ever tried anything similar?

[rwest]

Originally Posted by icarp

Icarp here, at 80 mph I run my adjustable reg at x psi to achieve 28 mpg @ 15.2 afr

The x psi is to not put a reference # , I have cams and an adjustable WUR in my cockpit .

Start psi 30* cold is 17 psi, 80* is 27 psi driving is 29.5 to 31 psi control pressure .
This is according to my gauge . stomp on it AFR is 12.8-14.0

works like a charm

Ian

Thanks Ian,

Exactly the sort of data points I was looking for.

[rwest]

Originally Posted by eastbay

I have one on my current 74 2.7 with CIS, not stock.
(JE pop ups-964 cams-ported heads by CGarr, etc)

I have mixture set to: idles mid to high 13s

will see 14-16s on very light throttle cruising
mid to low 13s on medium throttle
drops into the 12s on heavy throttle

The AFR gauge says it is good to .5 of AFR and I think it reads leaner than it is.
(mileage stinks)

I tried to buy a PMO EFI system right when they were sold, Richard called me and said 'sorry, can't fill your order'

I follow your thread with interest as I will go EFI sometime in the future.

Thanks Eastbay,

I’m getting closer and would gladly share any information I acquired doing the conversion.

Why do you think your mileage is bad? Is it the modifications you made or is something out of wack? I saw 19mpg for mixed driving and 26-27mpg on long trips with a stock 2.7 CIS.

I had a 1971 2.2T engine in an 69S body just out of HS with Zenith carbs and probably low compression that returned 37mpg on a trip to Chicago! Thought the gauge was broken.

[fanaudical]

I have a '75 911s with a mostly-stock 2.7 (CIS pistons and cams, larger oil pump, SSI's, SST air box) and have an AFR gauge installed. It's tuned to idle at AFR = 13.8 (which should correspond to 2.0% CO). I'll pay more attention next time I drive it and report back...

[jac1976]

Originally Posted by PeteKz

Rutager: Be careful what you ask for...

A number of us have AFR gauges on our CIS cars. I do, Icarp does, OldH2S does, etc. In my experience, and those with whom I've compared notes, the AFR is all over the place. You would think that the WUR should make the AFR go lean under cruising and off throttle conditions, and go rich when you put your foot down, but it usually seems to do the opposite! This has led several to install manual pressure valves to replace the WUR. I'm considering the same, except that I understand there is an electronic version soon to be available that will do what the WUR is supposed to do, but more reliably and adjustably.

Why are you asking?

Curious with regard to the electronic version.

[fanaudical]

There's a long FrankenCIS thread here somewhere:

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/820323-digital-wur-plus-frankencis.html

I have looked at building something similar; haven't bothered to finish it.

PeteKz - What electronic WUR are you looking at?

[Old H2S]

Old Fart here, my numbers concur with Ian... finally, after tearing off all the CIS add on's. I got the FD and cold start injector set up manually. 20 inches of Hg. at idle now, smooth...

[PeteKz]

Similar experience as Ian and OldH2S. Part throttle cruising at 70MPH yields AFR in the mid-15 range, and 29-ish MPG. What limits how lean you can go is surging/hesitation.

I don't know any more about the electronically adjustable WUR than a rumor. Maybe someone else can add more info.

[rwest]

Thanks so much guys.

Once I have my VE table in good order, I’ll slowly see if I can get to mid 15s during cruising while still getting good running. Should be fairly easy to do.

Rutager

[Dr J]

Originally Posted by rwest

Thanks so much guys.

Once I have my VE table in good order, I’ll slowly see if I can get to mid 15s during cruising while still getting good running. Should be fairly easy to do.

Rutager

From what I have read, the trick to go leaner is to advance timing. Haven’t had a chance to experiment yet but will try it in the future.

[AndrewCologne]

Originally Posted by Dr J

From what I have read, the trick to go leaner is to advance timing. Haven’t had a chance to experiment yet but will try it in the future.

The other way ... if you go leaner you advance the timing to hit the spot of the most efficient flame front building timing. Leaner fuel ignites/combusts slower so an advanced spark ignition compensates this. This is btw why many dizzys come with the vacuum cans. If in the manifold the vacuum is high (cruising or getting of the gas rapidly) this results in a lean mixture so the vacuum advance gives the optimal spot for igniting the current mixture AFR.

[Dr J]

We are saying the same thing Andrew. We agree that when you go leaner you advance the timing.