Originally Posted by mashtun
A Sierra one is 8" (assuming the measurement isn't across the full width of the unit including the seam joining the two halves, but 8.5" if it is). The unit in an M50-engined E36 appears to be 10" (a bit awkward to measure it in situ though).
Thanks for that. I reckon the Metro is only 6.25" at most.
Assuming that servo boost is relative to surface area of the diaphram then using the 10" BMW as a base the relative boosts are:
Metro - @6.25" = 39%
Sierra - @8" = 64%
Dual - @2x7" = 98%
BMW - @10" = 100%
If the above is an accurate reflection of the boost available it helps explain why the Metro servoed brakes require significant foot pressure to make them work.
Does anyone have a different take on it?
I am now very interested in following up the Dual 7" as I think it could be made to fit, with a little care and ingenuity.