Technical Ospho for headers or best exhaust for early Dart

no, it's a later A body.

 

Yep I might still go the 273 manifold route. I’m stubborn and can’t let a good challenge go. I’m confident I can built a good set of Tri y headers probably heavy ga SS. Down the road I want a fairly stout 318 or 360 not real hard to get 400 hp which will fill my need for speed. At less 3000 lbs and no power accessories it should be fun. My original goal was a roller 360 400- 450 hp but life happened and some of my funny money funds went away. I’m at the point I just want get it on the road and have some fun.
Dan

 

Like Moriarity, said, your not going to feel the difference on a street driven car, because of a difference between the size of the exhaust ports on the different sbm manifolds. Most flow restrictions don't even come into play until you reach the upper rpm range. You just don't see those on the street too much, but even then a short shift to 2nd (at 4G) will solve the problem.

I ran a .030 over 318 through small port 318 heads, that were match ported to the intake, with a 510 lift 294 duration Mopar cam, through a set of 70s era factory exhaust manifolds (class rules), on a 1/2 mile dirt track. It was a bear coming out of the corners, and it flattened out just before entering the next corner. The next year we swapped the 318 heads for a set of 340/360 heads using the same iron manifolds (intake and exhaust), pulled strong until the driver left off the gas pedal.

The exhaust manifolds will not be a performance issue if the exhaust after them is not too restrictive. The small intake ports on the 318 heads become a problem past 4500 rpm.