After a long web search, I found one rebuilt caliper listing which actually gave dimensions. 70 m.m. piston claimed. That's 2.750 diameter which is 5.965 sq./in. Looking at the Dr.Diff 4piston X 1.75" caliper kit. 4 pistons X 1.75" dia. equals 9.621 sq./in. That's 61% more piston area. The same master cylinder output pressure acting on more sq./in. is more clamping force albeit with more required volume. Just exploring options right now. Brakes are -"OK"- now, but not great.
if pressure and volume remain the same there won't be more clamping force with more area. i've been thru this. but, worse come to worse you can always swap parts back. i did a 2.75 caliper piston once with a 1" bore master cylinder; hard pedal and poor stopping. went to a 2.5" piston and a noticeable difference. tried a 15/16" master to get more pressure and it didn't work as good due to not enough volume with hard stops. settled on 1.031" master with the 2.5" piston; isn't great by any means but a lot better than the 2.75" with 1" master.
