I am upgrading my system to a MSD 6AL ignition box, MSD dist and the MSD coil from an Mallory dist. witt the old accell coil. What difference in performance can I expect? I have been told that I will notice a differencee in performance with the better ignition. I know some of you have seen differences, what can I expcect.
I have a mildly modified 454 cu in.

If your previous ignition was properly adjusted and in good shape, you'll probably notice no gain at all.

I am upgrading my system to a MSD 6AL ignition box, MSD dist and the MSD coil from an Mallory dist. witt the old accell coil. What difference in performance can I expect? I have been told that I will notice a differencee in performance with the better ignition. I know some of you have seen differences, what can I expcect.
I have a mildly modified 454 cu in.
The MSD-6AL box has - multiple spark below 3000 rpm (helps modified engines that want to load up at lower rpm) / more priecse spark+timing control ( helps
at high rpm) / rev limiter (keep from blowing the darn thing up! you can feel good about this if nothing else)

Ive always heard the replys of there wont be any difference, but real world results would be interesting. Im updating to an all msd system when my car gets back together too but there will be so many other changes itll be hard to tell if the MSD is the reason or not. Have you run your car at the track so you know what times itll run? Id be interested to hear what numbers you would run now.

My guess is that if you had a well tuned HEI system before an MSD will help for about 10-15 HP.. With a steadier idle., but then again.. who knows..

I have not ran my car at the track so I don't have any times. Like yourself, I am making so many changes to my engine I will not be able to say the MSD made all the difference. Can't wait to get my car back together to see just how much difference it will be.

My guess is that if you had a well tuned HEI system before an MSD will help for about 10-15 HP.. With a steadier idle., but then again.. who knows..

Where would this 10-15 hp come from? At any rpm above about 3000 the MSD produces only a single spark, the same as the HEI. If the timing is correct and the electronics in working order, it makes no difference what system produces the spark.