914/4 914/6 brake master cylinder, Difference? Options

[Driver174]

I’m looking at a FTE master cylinder for my 1974 -4, and website says it’s for a 70-70 six, and is not compatible with my car.

I’m curious as hat the difference is between the -6 and -4.

I rebuilt my complete brake system including an ATe master cylinder two years ago, and now needing to replace the it already. Was told the FTE unit had silicon seals and would withstand the heat better than seals in the ATe.

Your thoughts are appreciated

[flxzcat]

I use the 23 but I like a stiff pedal, oh, and I use Brembo Alfa front and Mercedes rear calipers.

I have a new uninstalled Ate 19mm that I purchased late last year before I found the 23mm----$200 +shipping?

[zoomCat]

I use the 23 but I like a stiff pedal, oh, and I use Brembo Alfa front and Mercedes rear calipers.

The force at the pedal required for a given clamping force is a function of the ratio of the caliper and master cylinder pistons. If you balance things out then brake pedal effort will change little. The factory brakes /6 have both larger calipers and master cylinder, but the ratio is little very close to the same.
Interestingly the hydraulic line pressure does change, largely based on caliper piston area, which is why the six has a different pressure regulator and why racing applications often replace the it.