123 ignition timing with USA emissions system

[Nicolas Aristodemou]

Numerous posts in this forum on the issue and still have an unresolved issue, maybe created through a thorough study of the various relevant posts and manuals.

I have a 1970 280 SL with working emissions control system in which I have replaced the Bosch 062 distributor with an 123 6RV unit (non programmable) in Nov 2019 set the unit for curve E and set the timing by ear, advancing the unit for max rpm and then slowly retarding it until rpm dropped by about 150rpm to the normal idling speed of just under 800rpm. I run the car with this setting for over 1 year, covered several thousands of miles car run smoothly and did not ping. Performance was very good. Throttle body is the later type with the constant vacuum being switched on and off by the vacuum valve at 2400/2200 rpm as it should.

Recently when I totally stripped and rebuild my engine with new cylinder liners, pistons, bearings, timing chain etc I set the timing of the new engine in much the same fashion, starting from a static setting of 8 deg BTDC (green LED of 123 unit just coming on) and  “fine” tuning the car by ear once more. Engine runs fine again is currently being run in.

Yesterday in late afternoon having some spare time and armed with a xenon timing light -normal unit non adjustable- I decided to see what kind of timing figures I was getting. I marked with white marker paint TDC, 10 deg BTDC on the right side of TDC mark and 10 deg ATDC on the left of the TDC Mark.

I checked the operation of the vacuum switch by connecting a vacuum gauge with a T connection between the distributor and the vacuum valve. I could clearly see around 17-18 inches of vacuum at idle and at 2400 rpm using an external electronic rev counter I could see the vacuum suddenly disappear completely and come back at 2200 rpm upon decelerating slowly. I could also feel the valve vibrating at both on and off points.

To my surprise the idle timing I had previously set (by ear) was shown by the timing light to be at 6 deg BTDC and trying to retard the timing to anything ATDC was simply not an option. The car wouldn’t run properly and was very hesitant to rev up. These readings were of course with vacuum connected. I set the timing back to 6 deg BTDC and car runs fine again. So my question is why I need to have an idle setup of around 6 deg BTDC for the car to run properly when I read in the various posts and in MB figures that the setting should be around 2-4 deg ATDC?

Maybe I should add that with my current setting (6 deg BTDC at idle) I do get 35 deg at 3000rpm which remains constant at higher revs. If I disconnect the vacuum at idle the revs go up since I remove the vacuum retard and the timing advances further increasing the idle speed, which is again normal.

Apologies for the long post, just wanted to put down all the facts so I can understand why my cars runs best at a different than published timing setting.

[Facelvega]

Hello, I installed a 123ignition tune in My Pagode with a original distributor ..62 with vacuum retard.
The only model to install for that engine is the 123ignition tune. You are able to program exactly the curve you need including vacuum retard.
Alfred

[Nicolas Aristodemou]

Thanks Alfred, this is actually the way I am thinking to go. Although I have bought 2 years ago the pre programmed 123 Mercedes 6-R-V, I am about to order the TUNE model to sort out any problems.

Which curves did you use to program your 123? Thanks, Nicolas

[Peter]

Hi Nicolas,

I had exactly the same a few years ago.
Conclusion was: 6 deg BTDC is perfect, also for my car.
An official different setting was maybe a way to comply with the emission requirements.

Peter

[Nicolas Aristodemou]

Very good Peter, that is good news.

 My car simply refuses to run if I  set the idle timing at anything after top dead centre (ATDC) - vacuum connected of course. So at the moment I am running at 6 Deg BTDC, however I do plan to get an 123 Bluetooth to replace my preprogrammed 123 to be able to experiment and fine tune ignition timing at various engine speeds.

[Peter]

however I do plan to get an 123 Bluetooth to replace my preprogrammed 123 to be able to experiment and fine tune ignition timing at various engine speeds.

Nicolas,

Very interesting, please share your findings with us on the forum.

Peter

[Nicolas Aristodemou]

Sure Peter, I have the 123 tunable unit on order, should get in a couple of weeks I hope.

[Nicolas Aristodemou]

So an update on the process since my 123\TUNE+ (Bluetooth) unit has arrived last Friday but not installed yet. My car is a 280 SL with emissions control in working order (Vacuum valve operating ok and controlled by speed relay (and 123 ignition pre-programmed at program E). I intend to do the following and would like feedback from the forum on my plan forward.

1. I will install the new 123\tune+ at 9 deg BTDC as per instructions using the green LED inside the unit to confirm static timing.

2. I will download the attached curves for centrifugal advance and vacuum advance, yes advance in this case. If you look carefully at the attached curves I use the ported vacuum - which is always there because of the design of my throttle body- to advance the ignition timing by 10 degrees -not 20 deg as per original Bosch 062- (starting at cranking speed) until the vacuum valve would switch this vacuum off at 2400 and the vacuum advance would disappear.  Looking at  attachment 1 at the centrifugal advance curve, the centrifugal advance goes up by 10 deg to offset the shut off vacuum. So at 2300rpm I program the centrifugal advance to increase by 10 deg since that will soon be offset by a 10 deg retard from vacuum valve vacuum shutoff. Ideally I would have programmed for 2375rpm + 10 deg centrifugal advance but 123 software only accepts multiples of 100rpm so I went for 2300prm.

3. I hope that this way I will have 9 deg Static + 10 vac advance + plus the centrifugal advance according to rpm up to 2300rpm (seen on my curves) and from 2400rpm onwards 9 deg static plus up to 29 deg centrifugal advance ie a total of 38 deg ignition advance.

4. I am doing this to keep the 2way vacuum valve operating as well as  the rest of my emissions control system. In the process my ignition system would become a vacuum advance system - since this can be achieved using the 123 built in software and mobile device App-.

5. Of course I could bypass the vacuum valve and connect directly the 123 distributor to the throttle body ported vacuum in which case I wouldn’t have to increase centrifugal advance by 10 deg at 2400 rpm and at the same time I would limit my max centrifugal advance to 19 deg so my total advance  would be again 38 deg (9 static+10 vac +19 centrifugal).

6 A final option would be to ignore the ported vacuum and switching valve all together, still connect vacuum to the 123 for originality but program the 123 to have only centrifugal advance and ignore any vacuum inputs. Something like what is shown in the second attachment.

Sorry for the long post, I just wanted to be as clear as possible. Maybe in the end I will try all three scenarios and see which would work best 

[Nicolas Aristodemou]

I finally replaced the pre programmed 123 model 6-R-V with the Bluetooth programmable unit. Old one for sale now, no use for it.

What a difference!!!!

I was able in 20 minutes to set it up properly and then another 20 minutes of highway high speed fine tuning using the TUNE feature of the App while I was moving.

Since there was no point in using the vacuum input to the distributor because of the freedom given by the  software programming, although I left the vacuum connected (through the vacuum valve) I have chosen to ignore this input.

As you can see from my attached curves vacuum curve gives  0 advance at all speeds hence ignored.

Since the App display shows the engine vacuum to the distributor I can see the vacuum valve switching vacuum off at 2400rpm and back on at 2250rpm but that is all.... just to know vacuum valve works (no problem if it hadn’t worked!) but no effect to distributor advance.

Maybe I should add that I had installed the unit as per manufacturer’s instructions with a static timing of 8 deg BTDC.

From there on it was a case of fine tuning at various rpm using the App on my iPhone.

Below are the maps that worked for me.

[Peter]

Nicolas,

Do I understand well that that at idle (750 RPM) the setting is +/- 8,5% BTDC?

Peter

[Nicolas Aristodemou]

Yes Peter, my car is automatic it idles at about 850 in neutral and about 600 in gear. Car run beautiful with this setting. About 8 deg BTDC, correct.

[Peter]

I am now on 6% BTDC, I am going to try 8% BTDC.

The official setting is very different I think, is there a downside?
Engine damage?

Peter

[Nicolas Aristodemou]

Peter I think the official 2-4 deg ATDC was for emission control purposes. My engine simply refuses to run at that setting, it simply dies away.

I wouldn’t worry about increasing 6BTDC to 8BTCD at idle. You cannot harm an engine even if you overadvance at low rpm. It’s overadvancing  at high rpm that will do the damage. But pinking on these engines is quite audible.... so it will warn you...

The beauty of the programmable 123 is that you can choose your map at all rpm ranges by adding point sets. Rpm vs deg of advance..... even nicer is that you can test and alter settings while driving so you can have immediate feedback.....

[Nicolas Aristodemou]

Maybe I should point out that I am using 98 Octane petrol, like in all my classic cars.

Should one be using  95 or lower octane petrol, maybe these advance figures should be reduced by 3-4 deg, especially on the higher rpm range.

[Peter]

I certainly wouldn't use 95 in Europe. It has added max. 10% ethanol.

For 98 that is max 5%, but some oil companies do not add ethanol, this can even differ per country (see their website).

Peter

[Nicolas Aristodemou]

Fortunately no ethanol into our petrol in Cyprus.......we enjoy that as long as it lasts......

[Mike Hughes]

Well at least you can get 95 and 98 octane fuel over there.  The best we can get on this side of the pond is 93 and my 230SL doesn't like it too much, or at least that is what I hear from under the bonnet when accelerating and going uphill.  Adding some octane boost at each fill up and using ethanol-free fuel keeps the maraca players on hold, but the volatile elements in the octane boost seem to evaporate away if the car remains parked for a while, and they resume playing!

[Nicolas Aristodemou]

Great sense of humor Mike.....

I never understood the reasoning behind the lack of high octane fuel in the US. I know that a lot of cars made in US have low compression engines hence octane rating is not that important. On the other hand higher compression ratio in a given capacity engine means greater power output and higher efficiency... doesn’t it?

[Tyler S]

Good read. Keep in mind that the more advance you have at idle, the leaner you can adjust your idle mixture. The byproduct being extra heat. Timing and mixture both have a cause and effect with each other.

[Peter]

And, more heat can result in burnt pistons ........?

So is the conclusion that you have to be careful to adjust it too lean?

Peter

[Nicolas Aristodemou]

Peter I do not think that aggressive leaning can cause overheating, on the contrary, when you get past the “best economy” mixture and lean even further engine temperatures will drop. See attached graph for a 4 stroke engine.

Of course in the case of the W113 engines I doubt that you can get leaner than the best economy setting. Even that would be difficult to achieve and keep the engine idling smoothly. Pagodas like reach mixtures and going lean starts have running and smooth shifting problems in automatic boxes.

Burned or otherwise damaged pistons would result from sustained operation at higher revs (for example highway driving) with too a advanced timing setting.

[kampala]

Well at least you can get 95 and 98 octane fuel over there.  The best we can get on this side of the pond is 93 and my 230SL doesn't like it too much,

The European octane rating method is different than USA- the actual real octane  is about the same - different calculation methods are used but premium fuel is almost equivalent in octane between USA and Europe. 

Europe uses a raw RON figure for rating where USA uses an average of RON and MON - but fuel real octane is about the same.