Well the MSD SCI is the exact same thing as the 6a. I even have an email from the MSD people that told me that they were the same cause I was wondering what the damn difference was. Anyhoo the system doesnt replace the distributor it just wires into the coil and to the battery. The only way they will make "better" gains is by buying any of the MSD external coils (I reccomend the blaster SS coil) and the modified distributor cap. Then getting some Magnecors and some NGK Iridiums (thsoe are optional) then tuning your ignition to the point of detonation then 5 degrees back. But to answer your question yes they are good but they are amazing when completely built. Oh yeah most internal coils are pretty weak in their spark producing power. :cheers: