1972 340 challenger

Actually you have this in the wrong forum. You need to post this in the engine performance forum. You'll get more responses there.

I'll tell what little I know but I'm mostly a trans. guy. Yes they were detuned due to lower compression and lazier valve timing. From what I understand they lowered the compression by lowering the pistons in the bore so a piston swap will raise the compression back up to 70 specs. Your heads should have the 1.88 intake 1.60 exhaust valves. Depending on how much HP your looking to make you may want to have larger 2.02 inch intake valves installed also. The cam is probably also smaller. I know my 72 340 idled smooth as silk and I heard a stock 68 340 the had a noticeable rumpety idle and I read the specs on their cam so you may want to swap to the 70 cam also. Wheather you can get all this in a kit or not I don't know. I'm sure you can get it seperately. Maybe try Mancini Racing at www.manciniracing.com/ they have alot of stuff.

And after all this you'll probably need to recurve the distributor and possibly rejet the carb for max performance but those are minimal items.