Hi All,
I decided to compare master cylinder area to total caliper piston areas for common Z part combinations and apply hydraulic principals.
Note: The total caliper area is the area summation for all pistons in both calipers.
From the data, it is clear to the Sumitomo 4 pot (Toyota S12-8) caliper upgrade has minimal area change from stock (2%) thus there is no significant change in required pedal pressure nor pedal travel.
With reference to the table, the common upgrade to a 15/16" master and S12-8 calipers will increase pedal pressure by 11% but reduce pedal travel by 11%. For a 240z or 260z, this will reduce pedal travel from 140mm to 126mm (which is what an 82 280zx's stock travel is)
Stock brake pedal strokes
72 240z: 140mm
74 260z: 140mm
75-78 280z: 123mm
82 280zx: 125mm
Pedal height from floor is 203mm
Examples:
adding a S12-8 calipers to a 72 240z will increase pedal travel from 140mm to 143mm
adding a S12-8 calipers and 3/4" master to a 72 240z will increase pedal travel from 140mm to 195mm (not good as maximum travel is 203mm)
Data:
Stock Datsun 240z to 280z caliper has two 53.98mm pistons (I could only find 72-78 data)
S12-8 caliper has two 42.82mm & two 33.93mm pistons
S12-W caliper has four 42.82mm pistons
I hope this is useful