As long as you can light the mixture, a hotter spark will not increase HP. Cylinder pressure and rpm levels determine the amount of energy to jump the gap on a plug. You have to ionize the air between the gap to build a spark. An MSD digital 6 box will fire most normally aspirated engines if it is working correctly. Supercharged turbo etc. may need more spark. Just because OEM engines use big plug gaps, does not mean performance engines need to do so as well. .030 to .035 is all that is needed, leave the .060 gaps for your daily driver. The next thing is all the other stuff some of the boxes do. Electronic control of ignition timing is a very good thing in my opinion for a performance engine, as well as data logging capability, you can't make good tuning decisions unless you have good info to make them with. If it is a drag only car and you are going to spend the money something like the grid would be my choice, just because of all the other stuff it can do besides spark the plug.
So let the box match your performance level and wallet.
This ^^^^^^ assumes all is well in the combustion chamber. Sorry but it’s not. You can’t have too much ignition. I’ve tested it far too much to say it doesn’t. I have an engine on the dyno right now and once it’s sorted out I’m going to change to a 7 box. I’m betting it picks up power everywhere over the 6. We will see.
If the 7 makes more power than the 6 then it did not have enough spark. Have you ever run an ignition scope with your engines on the dyno? By looking at the burn time, you can see if it has enough spark. I have seen on my dyno that a cheap ignition module in a HEI, will drop 20HP really fast. But again watch the spark KV and the burn time and you will see why. Also many ignition boxes will retard the timing at higher RPM's and that is the reason for lost power not spark intensity.
Quick story, had a buddy years ago with a big block Camaro, 10 second car, just bought a Mallory unilite ignition system for it. Car made a good pass, second pass the plastic shutter wheel broke. My buddy was mad that his weekend was ruined. Bought a single points distributor from the swap meet also going on at the event. Used the Mallory coil, went into town got a new set of points, car ran just the same. My buddy could not believe it.
