Brake master cylinder

[firehawk]

With a larger diameter master cylinder, you will be moving more fluid with the same pedal travel, which translates to longer piston travel at the caliper. So the pedal will be harder to push and there will be less transition between "slowing down a bit" and "dropping the anchor". Not very nice for a street driven car, but for driving on a track or racing, where most of the braking is of the latter kind, it may be worth it. Shorter pedal travel for same braking effect may also be useful when rev-matching using heel-and-toe.

Of course, when using brake calipers which have a larger fluid volume than the original ones, a larger master cylinder is quite necessary as the original one would result with a spongy pedal feel and perhaps even worse braking performance than with all-original brakes. MR2 Turbo twin-piston calipers with a stock AE82 FX-GT master cylinder was absolutely rubbish to drive and hard braking required the pedal to be put all the way to the floor.

Naturally, a full pedal box would fix all the problems and offer a multitude of adjustments for pedal travel/position and brake bias but they are quite expensive and in most cases on the street and in some racing classes, not allowed.