MSD 7531 or 8973?

Both systems have the same basic root software and do just about everything the same except the 7531 records the ignition data (called Launch History) going down the track because it is required for the slew rate rev limiter. Since you have the Racepak and if you are not going to or not allowed to use traction control then the decision maybe more towards the 8973. Everything that the 8973 has is in the 7531 and other then two items I talked about above everything in the 7531 is in the 8973. The only other minor difference that I know of is that for the Individual Cylinder Timing mode (ICT). The 7531 will select a firing order from a standard list and set the sequence up correctly where as the 8973 does not and you need a cheat sheet to know which cylinder in the program relates to what cylinder on your motor. No big deal. It sound worse than it is.

Go up on http://www.msdignition.com/1softdownload.htm down load the Pro-Data software. This software contains the softare for all these systems. Then select the 7531 or the 8973 then go to the HELP file for either and select either the 7531 or 8973 "Editor" and print it out and read and compare both. That Editor file has the most information that you will find for either system.

 

According to the wiring diagrams the 8973 uses the GREEN wire only out of the generator connected to the BRN/WHT input of the 8973 via the CLEAR wire but the 7531 uses the VIOLET wire only out of the generator and not the GREEN and is hooked to the GRAY of the 7531 or the TACH OUTPUT of the 7531. I will have to ask MSD what the difference is but they both work. Both have the VIOLET/GREEN crank trigger outputs directly hooked up to the Ignition boxes

 

According to the info I have. I will double check with MSD next week just to make sure.

 

On the 8973 the ICT is listed sequencially as 1,2,3,4,5,6,7,8. But you firing order maybe 1-3-7-2-6-5-4-8. So you need a cheat sheet when you adjust the ICT so you know that 1 is 1, but 2 is really 3, 3 is really 7, 4 is really 2 and so on. On the newer MSD Digital units like the 7531 they have all the basic firing order programmed into the unit so you select which one you want so you see the correct sequence when you look at the software. Why they can't do that in the 8973 really confuses me because it is just software.