Headers VS Manifolds

There is no difference in the 273 & 273 Commando exhaust manifolds.The 273 Commando got a 4bbl,higher compression pistons,and a higher lift cam.Thats the only difference.

The 273 and 318 share the same "small" intake/exhaust ports.

The 340 and 360 share the same "larger" intake/exhaust ports.

Bottom line: Put a set of "smaller" port 273 exhaust manifolds on your "larger" port 340 heads and you will choke your engine.