Large bore means lots of foot pressure to achieve same pad pressure. That means lots of stress on pedal, firewall, booster and MC. That’s a recipe for a mushy pedal. Smaller bore means less foot pressure to achieve same pad pressure, but more pad travel because the smaller bore has trouble pushing the same fluid volume.
[quote=“ctbimmer” post=73307]How about sticking with OEM fitment, which can be ATE or Girling, but are both legal.
I’ve always understood that the booster and MC must be same brand (no mixing) but otherwise no functional difference between them.
An oversize MC is not legal.[/quote]
It’s not that easy. I found MC’s advertised as OEM fitment with bore sizes all over the map. I also found multiple specs for OEM bore sizes. There was no clearly unimpeachable source of the spec. All I had was a bunch of “maybe’s”.
Booster and MC can be mixed and matched. There’s all sorts of booster’s and MC’s available on the market that say they are OEM fitment, but there’s no references to “ATE fitment” nor “Girling fitment”. A couple months ago, because folks told me that the shell of Girling boosters were less likely to distort, I swapped out my ATE booster for a Girling booster. I’ve no idea what brand my caliper was, I’ve gone thru several calipers on several cars over the years. The booster swap went fine. But the shell of Girling boosters is every bit as flimsy as the shell of ATE boosters so the swap was for naught.
