123 Ignition Curves for '71 280SL

[Woodstock]

I have installed a bluetooth 123 Ignition system on my car. 

I have set the advance curve per factory specs per the factory manual

The vacuum curve is the curve which we are having an issue with.  Per the bluetooth phone app the car has -.5 bar (MAP) vacuum at 800 rpm.  Would like to know the best setting to use for this curve.

The car runs with the current settings however it does not accelerate as well as it did with the stock points distributor and I am relatively certain that this is related to the default vacuum curve settings currently being utilized.

Any help in this matter would be appreciated.

Randy

[Pawel66]

This is the help I received from Tyler. I have March 70 car (retard at vacuum car) and it worked for me.

https://www.sl113.org/forums/index.php?topic=25879.msg185299#msg185299

I think: forget the whole advance/retard plot and just measure with stroboscope light what you get on the scale.

[dirkbalter]

Hi Randy,
As I recently learned and you probably know, the late 280’s operate with a constant vacuum port and a two-way valve to shut off the vacuum @ 2500 rpm. The earlier ones operate the vacuum retard with max vacuum at idle and “loose” the vacuum as the throttle flap opens.  Does the 123 take that into consideration?

Dirk

[kampala]

As Dirk has mentioned, if your car is a late 280 (70/71) and if it is a USA model and not EURO, installing a 123 per 123 instructions may not work if ALL your emissions equipment is not working.

There are ways of making the 123 work:

1. make sure all your emissions equipment works  and use program per 123 instructions. (can very complicated and expensive)

2.  Replace throttle body to older 280/250 model so vacuum is not constant, but only at idle and use program on 123 for distributor 051.   

3. If you know what you are doing, plug the vacuum on your current throttle body and drill a port to match an older throttle body (euro model). the casting is already set-up for this, but needs a hole drilled and a simple brass nipple placed to hold the vacuum hose. You can also have this done by sending your throttle body to Gernold at SL-Tech who has done a few of these.  I did my own.

I did option 3 and car runs so much better.    Of course some will advise against modifying the throttle body. You decide after research or ship the throttle body to Gernold.    I drilled precisely, matching my 250sl throttle body.

I tried to repair the emissions, but it much better to just by-pass it all.  I left it all in place, just by-passed the vacuum system.

good luck,

 

[Woodstock]

Since the emission system on the car has already been by passed.  Simply plugging off the vacuum line seems like the best approach to getting the car to perform well with the 123 ignition system.

Thanks for everyone's input.

Randy

[dirkbalter]

Hi Randy,
I may be wrong but believe that the 123 will not work properly without any vacuum.
My emission system wasn’t working properly. I tried to fix it but eventually chose to remove it. I contacted 123 to see if their distributor can be programmed to work without vacuum or constant vacuum at all times. They replied and from what I understood, they require either a working emission – vacuum set up in which case a curve for your original distributor can be selected. Or a vacuum at idle, in which case you can choose a program to mimic a 051 distributor (for example).  Considering you have a fully programmable unit, you may be able to work around it.
I bought a 68 throttle body on e-bay to provide max vacuum at idle. Since my distributor needed replacement, I rebuild and used a 051 distributor from my 230. Car runs great. Knowing what I know now and also from what Kampala said, it is possible and rather easy to modify your throttle body by adding the needed vacuum port.
I am interested to see how your make out. Keep us updated.
Dirk

[Woodstock]

Will update when I get the settings sorted out.

Randy