Programmable MSD 6AL-2 questions

[68Cuda]

Originally Posted by SSLance

Or just tell me what I need the MAP sensor to tell the box what to do...where and when do I want it to add advance and where and when do I not want it to add advance?

Overall adding vacuum advance will make the car run better under "normal" driving and have no effect on performance under full throttle.

So your MSD boost graph in the menu is in PSI. 14.7 PSI at sea level is 0 vacuum... every 1 psi = about 2" of vacuum. So, 10" vacuum is about 10 PSI and 20" vacuum would be about 5 PSI... now, if that does not confuse you, the graph adds retard, not advance. So, not only is the pressure graph kind of backwards to conventional thought, so is the advance.
EDIT: I think this is because this is usually used for BOOST retard... for example 10PSI boost (only airplanes use inches of boost) would be 24.7 PSI absolute. 14.7 PSI absolute pressure is no boost AKA 1 bar, AKA 0" vacuum.

Make sure you have the correct MAP sensor (1 bar) and the setting for that is correct on the MSD.

So, if I want 15 degrees advance at 20" of vacuum, I set 15 degrees more initial than previous, set my retard to 0 for anything up to 5psi, then slowly ramp in 15 degrees of retard all in by 14.5 PSI. This would give you a linear 15 degrees of "advance" from 0 to 20". What is the best curve - I don't know. I think the stock distributers can give you somewhere around 20 degrees at 20". I would start with, maybe 14, see how it likes it, progressively try more. This will cause you to have a higher advance while at idle, but that is OK, it will idle a little smoother, take less throttle screw and be less likely to diesel when you shut it off.