I have a 78 with a 400, it has true dual exhaust with no crossover that the P/O did.

The driver's side exhaust sounds different and when i put my hand behind it i can feel the exhaust pulses.

The passenger side is much smoother and more normal.

Is this a compression issue? I'm really kinda lost with it. Hope it's nothing too serious.

 

It could be alot of things. Start off simple. Are you sure the plugs and wires are good? How about the cap? It could be something as simple as an ignition miss on that side. I would make sure the tune up is good before trying to trouble shoot any further.

 

i agree, check timing as well. if it doesnt change than look into a crossover or x pipe

 

A friend of mine also had a similar problem. He also had a lack of power too. I took a look at it for him and noticed that one of his spark plug wires was melted to his header. Just a thought.....goes a long the lines with what the other two said

 

I agree with the above, make sure the engine is running 100%. Timing, plugs, wires, fuel, etc. Then if you still have the problem, it could be a valve not closing all the way, (carbon build up, burnt valve, worn valve seat, etc.) or worn rings loosing compression on one cylinder.