123 Ignition curves

[rowingone]

Just installed the 123 Ignition in my 1972 911T MFI and looking for the best curves to use. On the advice of Dave on the forums here I did remove the Delta 10B cdi as it seems unnecessary and I was unsure it was functioning properly. I did a search but didn't find any curves specific to the 2.4 T MFI motor. I do live at 5200 feet and don't know if there is any adjustment I would make for that regarding timing.

[Schulisco]

At first glance take a look on this page, don't know if your dizzy is mentioned there :
Early 911 Distributors - Carbs-Fuel-Ignition (CFI) - Repair & Sales

These are the original curves coming from the workshop manual which should be your most important reference. be aeare the rpms given are dizzy/cam shaft rpms compared to other diagrams with crankshaft rpms...

Ian here (icarp) is the wizard according mixtures and ignition timing, even with 123. He will probably help you out. If you always on that height it probably makes sense to make an individual setup on mixture and ignition timing. Be very careful: The leaner the mixture the higher the risk of unwished and serious damage due to detonation/pre-ignition. There are more threads here concerning 123 and ignition timing.

Thomas

[rowingone]

Thanks Thomas . . and yes I have based my initial curve on the factory one for the 2.4 911T. It will be an interesting process working through this . . and I appreciate any help I can get. Unfortunately 123 Ignition does not provide any help with curves.

[Schulisco]

Yeah, 123ignition is not a very good help on individual tuning, but IIRC they already started to collect ignition curves for common used engines/cars.

Best solution for you is be to contact a tuning shop with solid knowledge on old carburetted and MFI cars or even these old 911's and have car a test bench connected with a lambda and a knocking tool to make an individual and best fitting setup for your car based on that fuel (octane) you're using and residing at your altitude,
The newer 3.2 Carreras with Motronic ECU have an "altitude sensor" for that which basically is a switch / pressure can to determine altitudes lower than 1000m/3000ft or above. When above the ECU leans the mixture by IIRC approx. 10%. But they also have a lambda control from 1980 on to manage altidtude as well.
This value also could be a good first approach on your individual setup. But never forget when you drive on lower altitudes to enrichen the mixture again by at least 10% and to adjust the timing as well if necessary. With a MFI for the mixture not feasible afaik. When you got a Tune version of the 123 you can programm two different timing setups and switch them on purpose.

These cars with either carbs or MFI run a bit richer than the later G body cars with CIS or Motronic and lambda control. The correct mixture is always a deal between the altitude, compression ratio, octane, ignition timing, power, fuel economy and driving capability. The higher the altitude the leaner the mixture hast to be, but with leaner mixture you're running more and more into the danger of detonation...

Thomas

[rowingone]

Thomas . . I am thinking about purchasing this on Amazon . . for what is costs to use a tuning shop I think I could accomplish the same thing as it is so easy to change things with the 123. GUNSON G4125 Gastester Digital for $250

[Schulisco]

Originally Posted by rowingone

Thomas . . I am thinking about purchasing this on Amazon . . for what is costs to use a tuning shop I think I could accomplish the same thing as it is so easy to change things with the 123. GUNSON G4125 Gastester Digital for $250

I also have the Gunson Gastester...it depends. For me as an owner of a lambda controlled US SC with a base setting of CO from 0,4-0,8% CO not really usable because it is not that precise enough. It's tolerance is 0,5% CO. But for carburetted cars with higher CO values it's precision will be good enough. Don't know the CO base setting value on yours, I suppose it will be also higher than on my SC and the Carreras. So it will work basically for you. But I always recommend to make cross check afterwards on a certified gas tester. What you definitlely not want is to run the engine too lean...this will create more heat and detonations on the engine, especially while you make an inspired drive up and down the mountains and listening the music from behind...

I suppose your engine is the MFI US 911/51 with 2.4ltr, then the idle CO setting is 2,5%+/-0,5%, on cruising it should be around 1,5-2%+/-0,5% CO, CR is 7,5:1 which is pretty low.
Ignition timing: idle 5°ATDC@900rpm, 38°BTDC@6000rpm (vacuum connected)

Thomas

[rowingone]

Thomas . . yes the spec for MFI co2 on my car is 2.5% plus or minus .5%. I like the idea that I could get it close and then have it tested by a more accurate meter.

[Schulisco]

Here you find more information about the Gunson...

https://forums.pelicanparts.com/12040024-post8.html

When you display the whole thread you get even more ...

[eastbay]

Don't waste your time or money on a Gunson gas tester.

Install a wideband O2 sensor.

I have installed a few AEM 30-0300 units and found them to be great, but many other types and brands out there

[rowingone]

Interesting idea . . I had not thought of this. So you would have a muffler shop install a bung and install the sensor when tuning?

[911obgyn]

Yes you need a bung for O2 sensor

[rowingone]

Is the location of the bung important or just the most accessible spot?

[Schulisco]

Yes, a wideband O2 sensor permantly installed on your car might be quite good idea, indeed.

I suppose your car has an early SSI(-like) heat exchangers to an exhaust with 2 inputs? Then you can either mount a single O2 sensor on one bank or - far better - 2 O2 sensors on every cylinder bank.
On the SCs & Carreras the original exhaust is a 2-in-1 pipe making a bend to the catalyst, after the bend the O2 sensor is placed and monitors all exhausts from the engine. The original narrowband O2 sensor was not heated so it could happen that it cooled down that much on low speeds or while waiting at traffic lights that it won't generate a signal unless it warmed up again when driving. Todays narrowband and broadband O2 sensors have a heating inside, so no more matter to mount it as close as possible. Too close is also bad due to high exhaust gas temperatures.

In general the CO value follows the mixture in a small interval in an almost linear curve, there are some diagrams and tables showing the connection between these:



https://www.mgexp.com/article/co-to-air-fuel-ratio-afr-table.149



https://www.endtuning.com/afr.html

Thomas

[rowingone]

Yes this is a good idea for my situation. I think it might make sense to have the muffler shop mount two bungs, one on each cylinder bank . .and then move the sensor from side to side to get the proper tune. I read somewhere that the sensor should not be mounted pointing down where water could collect and that makes sense.

[Schulisco]

Originally Posted by rowingone

Yes this is a good idea for my situation. I think it might make sense to have the muffler shop mount two bungs, one on each cylinder bank . .and then move the sensor from side to side to get the proper tune. I read somewhere that the sensor should not be mounted pointing down where water could collect and that makes sense.

Keep in mind that the O2 sensors are quite sensitive on mechanical shocks as they happen when mounting and unmounting. I would use two O2 sensors and leave them in and build or get some kind of a (electronic) switch to choose the bank to be displayed or even use 2 gauges for every bank. Or others may post here further ideas to handle this...

Another option: If your exhaust has only a single output - Innovate has a clamp with that you can mount an O2 sensor only on purpose on the exhaust port:
https://www.innovatemotorsports.com/o2-sensor-exhaust-clamp.html
Then you monitor all the exhausts from all cylinders.

Just seen - they also have a dual lambda gauge:
https://www.innovatemotorsports.com/shop-all.html?series_db=8
Didn't knewed that, could be a perfect fit for you...

Thomas

[icarp]

This is the best all around 123 dist curve
For 2.0 -2.7 ltr 911 engine

Put 0 in all MAP settings

[icarp]

No pics posting
Sorry

[eastbay]

Originally Posted by rowingone

Is the location of the bung important or just the most accessible spot?

I just follow where SSI put them. Leave the sensor in and run the gauge full time, very educational.

[JackkTheMackk]

Here’s the timing map i believe Ian is trying to upload!

[rowingone]

Here is the curves I currently have loaded . .in the garage it runs great . . tomorrow I will road test.