Is the Frame interchangeable between a 2002 S4 and a 2002 M750Sie? If not what's the difference? Thanks!
They are both ST based frames, but are listed as different part #s.
I'd guess the bracing was different due to the 4V heads on the S4.
They're not interchangable. The tubing between the side rails is completely different to clear the 2V and 4V injectors. You can't swap a 2V motor into a 4V frame (or visa-versa) without cutting and modifying these tubes.
One more difference is that the 4v frames have mounts for the radiators