W113 Pagoda SL Group > Electrical and Instruments
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
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