IIRC, the 57 has the rather flat top, the 55-56 much more round. It flows better than the early manifolds, I don’t know if Ted’s exhaust test did both.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Phil and Gary.  I checked with a friend who has been into 'Birds forever.  In checking his parts, he has an ECJ 9431-C exhaust manifold tagged as being off a '57 Bird driver's side.  He also has an ECJ 9431-A exhaust manifold tagged as being off a '56 Bird driver's side. 

Other than the casting number, I don't know the difference in the two castings.

IF anyone can reference Gil Baumgartner's authored Classic Thunderbird Club International Thunderbird Restoration Manual, you will likely be able to obtain more info.  I don't have access to the book at this writing.   

Hope this helps.


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

I have a couple nice ECJ 9431-A but no -C
Gary

Casting number ECJ 9431 C  Email me at phil@lakefrontflorida.com or call 352 223-4483 and ask for Phil