I have some questions if someone can shed some light? Do all HP exhaust manifolds for 383, 400, 440 big block engines have the same air flow? I bought a set off a 1974 Dodge Charger with a 400. Will these manifolds bolt up to a 383? Someone commented to me they are smogger exhaust manifolds.

If you could post a picture, or two, that will help get your answer.

Assuming the manifolds are HP big block, I would expect their flow to be very similar to the other years.

383, 400 and 440 manifolds will work on any big block.

If your manifolds look like the picture below, you're good to go.

Mike.

Odds are the 74 exhaust manifolds do not reach the same height on the top arch as the pictured manifolds. Those pictured are likely 68-70 (71 or 72?) HP manifolds. The 73 and up are not as high, and are more rounded. They are still pretty good as far as the manifolds are concerned, but not the very best, the 68-70 are probably a little bit better. For street use, I wouldn't go through the effort to search out the 68-70 manifolds to replace the mid-late 70s manifolds. The very best cast exhaust manifolds were off the early 60s Max wedge motor manifolds, then the 68-70 manifolds. The pipes after the manifolds matter too, at minimum you need an "H" pipe or better yet, an "X" pipe, both flow more exhaust the just dual pipes.

That said, the mid-late 70s manifolds are bunches better then the 67 or older low, flat, logs were as far as air flow.

I ran dirt track Mopars in a hobby class in the early 80s with big blocks. Our track rules required cast iron exhaust manifolds and 2bbl carbs. We ran the 68-70 and the 71 & up exhaust manifolds without issues.

I can't remember which driver side (70-71, 72-73) had less of a divider on the outside surface between the two middle ports. I've got a '73 at home that I should be pulling out on Friday so I'll take a loot. That is the only difference that I've seen between 1970 and 1973 until the late 1973 manifold came out. That looks like a '74-up and is quite different.

They will all bolt up. Photos or casting numbers would help tell if you've got HP's.
Depending on power level, H or X pipes may not matter. Engine Masters has done a bunch of testing on this and is worth watching before anyone buys an exhaust system.