72 340 pass side manifold
71-73 left side manifold had a 2.25 inch outlet, right side 1 7/8 outlet. But the pipes on both sides were only 1 7/8 (or 2 inch?) for the first couple of feet, then fed into 2.25 inch pipes. Not only that, but the driver's side pipe was indented for torsion bar clearance.
As for performance, I'm surprised someone hasn't posted the Mopar Muscle (I think) dyno testing of a 300 hp crate Magnum engine with different exhaust. According to them, the best 340 exhaust manifolds were only marginally better than LA 318 manifolds, and headers were only maybe ten hp better.
To that I would just cite my own experience: Back in the late seventies, I put a set of cheapie headers on my 73 Duster 340 that was stock except for a 71 intake and a 650 spreadbore Holley plus the factory heat riser was removed from the stock passenger side manifold. I didn't replace the rest of the exhaust system, which was completely factory original down to the original mufflers. The headers were worth seven tenths of a second in the quarter. Actually they were worth more, but now it had so much more low end torque that now I had a traction problem that I had not had before. Shifted at 5200 with the stock manifolds (and there was no point in going any further), shifted at 5800 with headers.
I had similar results more recently when I replaced the 68-70 340 hi-po manifolds with TTI headers in my 67 360 Barracuda with a slightly hotter than stock cam, Edelbrock RPM intake and 750 Holley, plus in this case I also replaced the 2.25 inch muffler shop exhaust with TTI 2.5 inch mandrel bent X pipe. Again, a huge gain in low and mid range, plus significantly more top end. So much more power down low that I couldn't give it full throttle in low gear without going sideways until I started running drag radials on the street.
I doubt that replacing the OEM 72 passenger side manifold with the early hi-po 340 manifold would really make much difference. At least, it didn't on my 65 Barracuda when I made that switch.
My two cents. Your experience may differ.
71-73 left side manifold had a 2.25 inch outlet, right side 1 7/8 outlet. But the pipes on both sides were only 1 7/8 (or 2 inch?) for the first couple of feet, then fed into 2.25 inch pipes. Not only that, but the driver's side pipe was indented for torsion bar clearance.
As for performance, I'm surprised someone hasn't posted the Mopar Muscle (I think) dyno testing of a 300 hp crate Magnum engine with different exhaust. According to them, the best 340 exhaust manifolds were only marginally better than LA 318 manifolds, and headers were only maybe ten hp better.
To that I would just cite my own experience: Back in the late seventies, I put a set of cheapie headers on my 73 Duster 340 that was stock except for a 71 intake and a 650 spreadbore Holley plus the factory heat riser was removed from the stock passenger side manifold. I didn't replace the rest of the exhaust system, which was completely factory original down to the original mufflers. The headers were worth seven tenths of a second in the quarter. Actually they were worth more, but now it had so much more low end torque that now I had a traction problem that I had not had before. Shifted at 5200 with the stock manifolds (and there was no point in going any further), shifted at 5800 with headers.
I had similar results more recently when I replaced the 68-70 340 hi-po manifolds with TTI headers in my 67 360 Barracuda with a slightly hotter than stock cam, Edelbrock RPM intake and 750 Holley, plus in this case I also replaced the 2.25 inch muffler shop exhaust with TTI 2.5 inch mandrel bent X pipe. Again, a huge gain in low and mid range, plus significantly more top end. So much more power down low that I couldn't give it full throttle in low gear without going sideways until I started running drag radials on the street.
I doubt that replacing the OEM 72 passenger side manifold with the early hi-po 340 manifold would really make much difference. At least, it didn't on my 65 Barracuda when I made that switch.
My two cents. Your experience may differ.