Using LM-1 on CIS
 

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?

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.

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.

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.

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.

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/426682-silent-killer-930-power-fuel-economy.html

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

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

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

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

http://forums.pelicanparts.com/uploa...1193524129.jpg

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?

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.

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?

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.

Retard disconnected.

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.

http://forums.pelicanparts.com/porsche-911-technical-forum/333640-distributor-service-clean-lube-real-easy-without-removing-pinion-gear.html

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.

Great, thanks!

"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

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.

http://forums.pelicanparts.com/porsche-911-technical-forum/427111-ignition-timing-new-964-profile-cams-3-0l.html

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.

Just to follow up I have been running numerous tests with an LM-1.

I currently have my CO set at roughly 3%. While driving the car I watched my mixture numbers and liked what I saw. Nice enrichment on WOT.

One question remains though, at 2300-3000 RPMs I see my leanest condition at14.7 AFR.

Is that too lean or is it still ok?

I'd say that's ideal for fuel economy and emissions.

A/F at WOT is open loop. That is, sensor input is ignored in this mode and the default is what is allowed by the ECU.

Sherwood

Been folling this thread closely... What if you have no ecu?? like my ROW? All I have is the mixture screw...

Comments Sherwood?

-Michael

Craig,

14.7 is stoich so your LM-1 would show it as "joosta right" for economy and emissions. More importantly, I think, is that stumbling you were getting. Has it disappeared w/ this setting?

Michael,

W/o an ECU you are relying on your mixture screw setting and the design of the CIS system to give you the best setup under all conditions. If you have an A/F meter you should find an idle setting of about 3.5% will give you best performance according to JW. I've always set mine by feel. I've found that if @ warm idle I get good pull up to redline and then the idle speed does not drop down before returning to the correct point, or if @ idle there is no hunting, then it's good. A recent test w/ an LM-1 confirmed this point is 3.5%.

For some reason I was thinking that 14.1 was stoich. Good to know that I am ok at 14.7.

Still have stumble. My troubleshooting was on pause this weekend since I had to do my final valve adjust. This was my first solo valve adjust - between changing the oil, sump plate, checking my cam timing, and putting my muffler back on it took me all weekend to complete. Not as fast as others b/c I am a noob.

Next step is to swap coil then dizzy. Again, I am not too bothered by it. Just want to make sure that I am not running too lean where I would be damaging the engine.

Four of us in the area are going to split the cost of an LM-2. I have been borrowing the LM-1 and it sure is a nice piece of equipment to have on hand.

It is easier. You can play with the idle adjust screw and fuel mixture screw. I have an LM-1 but with RPM sensor and it tells me I am fine at idle anywhere at between 14 and 14.7 I tbelieve that that gives you 3% and not 3,5% co but maybe it has something to do with altitude. I have seen numbers on this site that I can not match from people in Denver and that is pretty high up.

Stupid thing is you do not really need the LM-1 on a RoW SC. If the idle hunts at warm-up you are to rich if it stalls at warmup you are to lean. If you are in between and your warm-up is smooth then believe it or not the LM 1 shows 14.x. I would say the differen is about 1/2 a turn on the mixture. Ofcourse this is when cold start valve , AAV, Thermo time valve all work well.

I am at sea level. Car is a 1983 SC RoW no Ecu no 02, no mods.

AT 6000Rpm you want to have 12.7 or somewhere around that. I run 98 Octane.

One thing that made me go around the block several times was the decel valve. I could not get my idle stabilized even though all my numbers where spot on; until I swapped the decelvalve and the tubing. Turned out the decel valve membrane had a hole in it and let air through once every so now and then ;o)

Also one for the books I believe your timing needs to be excellent before setting the mixture. I was trying to do mixture with timing fairly far off and I did not get good results. Now this could just be me being stupid.

Michel