Using LM-1 on CIS

[mca]

I am preparing to check my mixture on my newly rebuilt 3.0 in an 82SC. A friend let me borrow his LM-1 which I used once prior to taking my old engine out. I was a bit uncertain about what numbers I should be seeing and I am looking for some clarification. I read the LM-1 online manual / instructions

Not sure if this matters, but the engine specs are:
9.5 cr JEs, 964 cam grind, SSIs, and a Dansk sport exhaust. I replaced the intake boots on the CIS, installed new injector o-rings, installed new injector sleeves and sleeve o-rings. The cam timing is advanced. Ignition timing is at 5 BTDC. O2 sensor is disconnected (and staying that way).

So with the engine warm and the LM-1 sensor clamped into the tailpipe, what should be air fuel ratio be?

[Scott R]

On a new engine why chance this? My LM-1 is wildly inaccurate compared to a regular gas analyzer. I just take a trip to my p-car wrench now and have them hook it up real quick.

[mca]

Originally Posted by Scott R

On a new engine why chance this? My LM-1 is wildly inaccurate compared to a regular gas analyzer. I just take a trip to my p-car wrench now and have them hook it up real quick.

I was planning on having someone check it out after I put some miles on it.

In the meantime I want to make sure that I am at least close to having the proper ratio.

[Gunter]

Originally Posted by mca

The cam timing is advanced. Ignition timing is at 5 BTDC. O2 sensor is disconnected (and staying that way).

So with the engine warm and the LM-1 sensor clamped into the tailpipe, what should be air fuel ratio be?

What do you mean by "Cam timing advanced"??

5 deg BTDC with advance and retard connected?? Or disconnected??
What is your ignition timing at 6000 RPM? That's the important one.
O.K. make it 5000 RPM.

As for the initial mixture setting, you might as well do it by ear:
Adjust fast idle to ~900 RPM.
Use the LONG 3 mm Allen and turn the adjust screw gently cw (Rich) until it affects idle, then turn ccw (Lean) until again effect is noticed. Now turn cw (Rich) half-way between the two extremes.
We are talking very little movement; 1/2 turn alltogether and it requires touching up the fast-idle screw to stay at ~900 RPM.
That should be good until you get a proper check.

[Paulporsche]

I posed this same question back in July and got almost no response. Maybe noone really knows?

I was thinking about 14:1 @ idle and 13.2:1 under WOT, but I've been unable to confirm. Furthermore, can anyone correlate AFR and CO%? We know JW likes 3.5% @ idle.

[willtel]

There is lots of AFR talk in the turbo forum, I think NA motors need slightly different numbers than a turbo engine but we talk about it all the time. Maybe some of this info will help.

The silent killer of 930 power and fuel economy.

[911pcars]

Originally Posted by Paulporsche

I posed this same question back in July and got almost no response. Maybe noone really knows?

I was thinking about 14:1 @ idle and 13.2:1 under WOT, but I've been unable to confirm. Furthermore, can anyone correlate AFR and CO%? We know JW likes 3.5% @ idle.

Those numbers sound pretty good. 3.5% is about 13:1 A/F. If the engine can idle and cruise smoothly with a leaner mixture, why not? One only needs the optimum A/F mixture for power at WOT.

Here are some numbers gleaned from the web:

From http://www.turborick.com/air1.html

% CO A/F RATIO %CO A/F RATIO % CO A/F RATIO % CO A/F RATIO
0.1 = 14.71 0.2 = 14.53 0.3 = 14.41 0.4 = 14.33
0.5 = 14.27 0.6 = 14.22 0.7 = 14.20 0.8 = 14.16
0.9 = 14.14 1.0 = 14.10 1.1 = 14.08 1.2 = 14.03
1.3 = 14.00 1.4 = 13.97 1.5 = 13.93 1.6 = 13.89
1.7 = 13.85 1.8 = 13.81 1.9 = 13.79 2.0 = 13.76
2.1 = 13.72 2.2 = 13.68 2.3 = 13.62 2.4 = 13.58
2.5 = 13.55 2.6 = 13.53 2.7 = 13.48 2.8 = 13.44
2.9 = 13.40 3.0 = 13.37 3.1 = 13.33 3.2 = 13.30
3.3 = 13.26 3.4 = 13.23 3.5 = 13.19 3.6 = 13.14
3.7 = 13.11 3.8 = 13.07 3.9 = 13.02 4.0 = 12.99
4.1 = 12.95 4.2 = 12.92 4.3 = 12.89 4.4 = 12.85
4.5 = 12.82 4.6 = 12.79 4.7 = 12.74 4.8 = 12.69
4.9 = 12.66 5.0 = 12.63 5.1 = 12.58 5.2 = 12.53
5.3 = 12.50 5.4 = 12.45 5.5 = 12.42 5.6 = 12.39
5.7 = 12.36 5.8 = 12.32 5.9 = 12.29 6.0 = 12.24
6.1 = 12.21 6.2 = 12.17 6.3 = 12.12 6.4 = 12.09
6.5 = 12.06 6.6 = 12.02 6.7 = 11.99 6.8 = 11.95
6.9 = 11.92 7.0 = 11.88 7.1 = 11.85 7.2 = 11.81
7.3 = 11.78 7.4 = 11.75 7.5 = 11.71 7.6 = 11.68
7.7 = 11.64 7.8 = 11.60 7.9 = 11.57 8.0 = 11.53
8.1 = 11.49 8.2 = 11.45 8.3 = 11.42 8.4 = 11.39
8.5 = 11.36 8.6 = 11.31 8.7 = 11.27 8.8 = 11.24
8.9 = 11.20 9.0 = 11.15 9.1 = 11.11 9.1 = 11.07
9.3 = 11.04 9.4 = 11.00 9.5 = 10.96 9.6 = 10.93
9.7 = 10.89 9.8 = 10.85 9.9 = 10.81 10.0 = 10.78

Hope this helps,
Sherwood
http://members.rennlist.org/911pcars

[mca]

Originally Posted by Gunter

What is your ignition timing at 6000 RPM?

Can't do that considering I only have 50 miles on the rebuild. Not taking it that high until I hit 1000 miles.

[mca]

Originally Posted by Paulporsche

I posed this same question back in July and got almost no response. Maybe noone really knows?

I was thinking about 14:1 @ idle and 13.2:1 under WOT, but I've been unable to confirm. Furthermore, can anyone correlate AFR and CO%? We know JW likes 3.5% @ idle.

Yep, that is why I posed this question again. Can't find a lot of info about it. Much debate about different meters though.

[Scott R]

This is my lm1 output from the dyno, was set to 3.5% no O2 connected on my 80.

[Paulporsche]

mca,

Sorry for the hijack. That certainly helps me at least. Thanks, Sherwood and ScottR.

Gunter,

Re timing--shouldn't the diz reach full advance @ 4000? This is what I've been recently told. Why is 6000 significant?

[Gunter]

Henry Schmidt told me that he would like 26-28 to 4800 and another 2-4 degrees for the remainder for my set-up.
Steve@Rennsport curved my distributor in a similar fashion.
I think max advance is reached around 5000 RPM.

Steve stresses that a lot depends on octane used, air temperature and CR.

[Gunter]

Originally Posted by mca

Can't do that considering I only have 50 miles on the rebuild. Not taking it that high until I hit 1000 miles.

O.K. make it 5000 RPM. No need to baby the engine. If everything was done correctly during rebuild, it should purr.
Measure from Z1 on the pulley across the 5deg and make a small mark at 35 mm with white paint.
With advance and retard connected, rev to 5k and see where the Stroboscope light hits near the mark.
Slightly left of it, like 33 deg is good.
You want to set the distributor so it has max advance at 5k and then let the idle timing fall where it may.

Still questions:
What do you mean by "Cam timing is advanced"?
When you set the ignition timing, do you disconnect the vac advance/retard?

[mca]

Originally Posted by Gunter

What do you mean by "Cam timing is advanced"?

Got some numbers from WebCam and EBS regarding cam timing - gave a range from retarded to advanced. Normally with the 964 grind the cams are timed at 1.26 mm. I don't recall right off hand what my final numbers were but they were on the advanced side.

Originally Posted by Gunter

When you set the ignition timing, do you disconnect the vac advance/retard

Retard disconnected.

[Gunter]

Cam-types have virtually no bearing on ignition timing.

If you have the stock Bosch 0 237 304 016 distributor for '80-'83 SC's, both advance and retard are disconnected when timing 5deg BTDC at ~900 RPM.
Once both vac lines are reconnected, the timing at idle changes if the vac can works properly; moving towards the retard side.

If your distributor has never been serviced in ~25 years, consider at least a cleaning and oiling the the mechanical advance plus weights/springs.

Distributor service (Clean and lube) real easy without removing the pinion gear!

[mca]

Originally Posted by Gunter

Cam-types have virtually no bearing on ignition timing.

If you have the stock Bosch 0 237 304 016 distributor for '80-'83 SC's, both advance and retard are disconnected when timing 5deg BTDC at ~900 RPM.
Once both vac lines are reconnected, the timing at idle changes if the vac can works properly; moving towards the retard side.

If your distributor has never been serviced in ~25 years, consider at least a cleaning and oiling the the mechanical advance plus weights/springs.

Distributor service (Clean and lube) real easy without removing the pinion gear!

I don't think that the advance line has any effect at idle. And I run without the retard line anyhow so that is why I set it with the retard disconnected (and plugged).

I do have another alternator that I am considering shipping out to be refurbished. Any suggestions for me regarding who should do the work? What about recurve?

[Gunter]

Originally Posted by mca

I don't think that the advance line has any effect at idle. And I run without the retard line anyhow so that is why I set it with the retard disconnected (and plugged).

I do have another alternator that I am considering shipping out to be refurbished. Any suggestions for me regarding who should do the work? What about recurve?

Correct. Advance has no effect.

If you mean a distributor service and re-curve, send it to Steve@Rennsport in Portland.
He did mine to run without vacuum, very nice.
Since the vac can is removed anyway, you can take it off and make a small cover plate to attach with the 2 screws like I did.
(The picture in your other thread is the distributor before the re-curve)
Steve would want to know CR, octane used, and average air temps to set the curve.
Send him an E-mail.

[mca]

Great, thanks!

[911pcars]

"Cam-types have virtually no bearing on ignition timing."

MCA was stating other engine parameters that could affect the ignition timing. Cam timing might be one of those. Starting the valve opening and closing events sooner (advancing cam timing) than specified provides slightly more torque at lower rpm at the expense of high end power. While an approximate ignition advance curve could increase engine efficiency for this modification, a road or chassis dynamometer is a preferred method of calculating the exact ignition needs of a specific engine.

Sherwood

[Gunter]

We're not talking about a maxed-out racing engine here.
The only changes made to this 3.0 with CIS were 964-cams and SSI's.
Stock SC cams for '80-83 have an overlap of 1.4 - 1.7 mm.
964 cams are about 1.3 mm and have just a little more lift than SC cams to stay compatible with CIS.
After discussing the issue in the past with JW and Steve, I timed my 964-cams at 1.4-1.45 mm essentially staying within the SC-cam tolerance.
However, I have 98mm P/C's 9.8 : 1 CR and have to be more concerned about correct ignition timing and use 92+ octane to avoid detonation.
A few knowledgeable engine builders stated that there is no concrete evidence about different torque values with slightly more or less cam timing for our street engines.

I can attest that there is a noticeable better performance with a re-curved distributor.

Here is a reply from Steve@Rennsport who has a lot of experience.

Ignition timing with new 964 profile cams on a 3.0l

Quote: "You do NOT change ignition timing when installing sportier cams."

"Ignition timing values depend on CR, displacement, and fuel."

"Idle timing isn't important; total timing at 6K (unless re-curved) is all that matters and that value depends on CR and what fuel you will use."


So, if folks with much more experience than I'll ever have state the above, I'll have to agree:
"Cam-types have virtually no bearing on ignition timing."
Besides, IMHO, setting a 964-cam at 1.3, or even 1.4 mm overlap is not advanced.