Firstfives.org

Having kept one from a parts car, the larger outlet size from the '79 surprised me. I.e., depending upon the year, or 3.3, 3.5 one exhaust manifold outlet is larger than another. Not necessarily larger for the larger displacement as the '79 is a 528i.

Thereafter requiring a cat inlet, gasket to match.

So, do we get all hot roddy and insist on the larger version ? Or is the difference of about 1/2 " in diameter not worth a broken stud bolt ?

The 79 is bigger because it's only 1 instead of 2, it's the one manifold feeds into another one with a single downpipe. Others used 2 downpipes. BMW was so concerned about it they used the same manifolds for both E12 2.8 and E23/24 3.3. In other words it might be measurable, or not, but I doubt it's detectable by feel. And this is coming from the guy who adjusts his valves to the tight end of the spec to try and gain every little .001HP.