it pts a cool red aluminum box on your firewall...plus gives hotter spark and multiple sparks during the power stroke, vs. the stock 1 spark, hence the name MSD-multiple spark discharge, thats all i know so good luck, and the 6AL has a rev limiter, the 6A does not
instead of firing once, the coil fires 6 times for each cylinder below 3000rpms and one big spark above 3000rpms. most coils loose power as the rpms rise, the msd box will prevent that, allowing for full voltage from the coil at all rpms
FWIW, the stock ignition is robust. It should be good for upwards of 400 HP N/A. And there is one guy in particular I know of who is running 10 pounds of boost with a stock ignition and not having flame out issue.
Basically if you have a N/A setup, or a mild build up, you don't need an MSD.
I am hooking mine up tomorrow, on my mild, n/a, 5.0...but I have my reasons. I want a hard rev limiter, which I will set at 6k...and I will be adding a power adder shortly, I just don't know which one.
If you want a cheaper alternative, I do have a ProComp 6AL (imitation MSD 6AL) that has never been used but has been opened. I bought it to save a few bucks ($140 for the ProComp vs $200 for the MSD), but the other day I was getting it ready to install and I heard a rattle from inside. So I popped the bottom cover off and found that one of the heatsinks was not fastened. There are two of them that are screwed to the case itself, and one of them didn't have the screw holding it down..the screw was loose. I decided to not put it in my car and will be putting it on eBay for $50 + shipping as soon as I get a picture.