I think the reason that the 46IDF then the 46, the the 48 IDA's were made as twin throats vs making one single four throat carb with the correct center to center bores to fit the SB Ford is a simple answer.
The throttle shafts on the carbs twist very easily. If you had one single long throttle shaft for each single "Weber" Inline 4 barrel, the end loading of the throttle would quickly have twisted enough so that it the throttle plate at the opposite end would be twisted hopelessly out of sync.
How the Porsche version 46-3 IDA's for the 911 S, three barrel carbs actually survive and function I don't know.
Did it ever occur to Weber to use a hardened steel shaft? I would have to presume, yes, but what the reluctance on that was, I don't know?
I do know that on the Ford with the four 48IDA's, you MUST actuate the throttles from the center of the assemblies and not the far end of the assembly.
It could also have been that Weber felt one single inline 4v was too specialized to the Fords and there wouldn't have been enough product demand for it, whereas dual throats ganged together was more of a modular/universal product?
The spacing evolved too being what was necessary at the time to install all of the operating hardware such as jets and emulsion tubes.
Sure, Ford accomplished that with the Autolite Inlines but their total approach was different...AND they weren't stubborn Italians?
As a result, you cast the manifold to mate the IDA's to the intake ports of the engine. If you look at some of the variations of the castings particularly on the 289/Boss 302 I clearly see that was somewhat of an frustrating engineering exercise for sure.
The Cleveland version of the manifold is actually a much better functioning manifold because you have a 9.2" deck height vs the tiny 8.0 or whatever on the 289/302 block.
The Cleveland manifold at least somewhat seems to recognize the "desirable" carb to valve runner length to work as a ram tune a little? I don't see where that effect exists on the 289 manifolds at all. Those ports are too short to give the effect?
Dan Jones was talking about that number. It is entered into his software "hp computer" calculation now. I want to say it is a minimum of 4.5".
The "Pantera Weber" manifold seems to incorporate that in the castings? Halls is a copy of the Detomaso manifold which is said was originally developed and built by "Holman-Moody" and sold or given to Detomaso?
That part of the history of the "Pantera Weber" manifold is still undocumented but unless you make your own intake manifold (
) you are stuck with all of that to work with.