23 mm Master cylinder?, From a 930? Options

[HalfMoon]

A friend of mine who owns a race shop that does alot of Porsche work said when queried about reducing travel on the 914 brake system that the 23mm master cylinder from a 930 would far better reduce the travel over a 19mm master cylinder.
Has anyone done this mod and if so, what were the performance gains/differences?
Thanks
D

[HalfMoon]

To clarify-

I run a 19mm too (as well as a variety of other big brake mods). The primary question I'm pursuing isn't brake "power" (performance gains/differences is/was ancillary), rather it's about "less pedal travel".
That's what the inquiry is really about as well as the advice I had been given.
So I guess the question is for folks who have ACTUALLY done the modification to a 23mm and if they have obtained less pedal travel as a result.
Not asking about theory or opinion, asking about actual experience. Many of us have done the 19mm change and their's reams of information on that mod but not much about the 23mm and pretty much nothing in terms of actual experience.
The main thrust of the question is "brake travel".

[mepstein]

To clarify-

I run a 19mm too (as well as a variety of other big brake mods). The primary question I'm pursuing isn't brake "power" (performance gains/differences is/was ancillary), rather it's about "less pedal travel".
That's what the inquiry is really about as well as the advice I had been given.
So I guess the question is for folks who have ACTUALLY done the modification to a 23mm and if they have obtained less pedal travel as a result.
Not asking about theory or opinion, asking about actual experience. Many of us have done the 19mm change and their's reams of information on that mod but not much about the 23mm and pretty much nothing in terms of actual experience.
The main thrust of the question is "brake travel".

The change in pressure and travel when you go to a larger MC isn't theory or opinion. Its a relationship/ratio between the size of the MC and size of the piston calipers. If you keep the calipers the same but increase the size of the MC, the MC will move more fluid with less pedal travel but at the same time, you will need more pressure on the pedal to achieve the same braking force at the caliper. Just like sitting on a see saw, shorten the lever on your side and it gets harder to lift the other end but the travel on your end is shorter. Go too short and at some point, you don't have the force available to move the lever. You also have to make sure the ratio front to back is correct. Its not just about going big, it's about the correct balance.

You won't see much information on World about 23mm MC's because most of the cars simply can't use a MC that large unless they've also switched to very large calipers.

[jd74914]

To clarify-

I run a 19mm too (as well as a variety of other big brake mods). The primary question I'm pursuing isn't brake "power" (performance gains/differences is/was ancillary), rather it's about "less pedal travel".
That's what the inquiry is really about as well as the advice I had been given.
So I guess the question is for folks who have ACTUALLY done the modification to a 23mm and if they have obtained less pedal travel as a result.
Not asking about theory or opinion, asking about actual experience. Many of us have done the 19mm change and their's reams of information on that mod but not much about the 23mm and pretty much nothing in terms of actual experience.
The main thrust of the question is "brake travel".

The change in pressure and travel when you go to a larger MC isn't theory or opinion. Its a relationship/ratio between the size of the MC and size of the piston calipers. If you keep the calipers the same but increase the size of the MC, the MC will move more fluid with less pedal travel but at the same time, you will need more pressure on the pedal to achieve the same braking force at the caliper. Just like sitting on a see saw, shorten the lever on your side and it gets harder to lift the other end but the travel on your end is shorter. Go too short and at some point, you don't have the force available to move the lever. You also have to make sure the ratio front to back is correct. Its not just about going big, it's about the correct balance.

You won't see much information on World about 23mm MC's because most of the cars simply can't use a MC that large unless they've also switched to very large calipers.

One small correction: You need to exert more force on the pedal to have the same brake line pressure due to larger MC area. A 23mm MC requires 1.47x more force for the same line pressure as a 19mm (needed if your calipers are unchanged during the swap). You also have 1.5x less travel.

[mepstein]

To clarify-

I run a 19mm too (as well as a variety of other big brake mods). The primary question I'm pursuing isn't brake "power" (performance gains/differences is/was ancillary), rather it's about "less pedal travel".
That's what the inquiry is really about as well as the advice I had been given.
So I guess the question is for folks who have ACTUALLY done the modification to a 23mm and if they have obtained less pedal travel as a result.
Not asking about theory or opinion, asking about actual experience. Many of us have done the 19mm change and their's reams of information on that mod but not much about the 23mm and pretty much nothing in terms of actual experience.
The main thrust of the question is "brake travel".

The change in pressure and travel when you go to a larger MC isn't theory or opinion. Its a relationship/ratio between the size of the MC and size of the piston calipers. If you keep the calipers the same but increase the size of the MC, the MC will move more fluid with less pedal travel but at the same time, you will need more pressure on the pedal to achieve the same braking force at the caliper. Just like sitting on a see saw, shorten the lever on your side and it gets harder to lift the other end but the travel on your end is shorter. Go too short and at some point, you don't have the force available to move the lever. You also have to make sure the ratio front to back is correct. Its not just about going big, it's about the correct balance.

You won't see much information on World about 23mm MC's because most of the cars simply can't use a MC that large unless they've also switched to very large calipers.

One small correction: You need to exert more force on the pedal to have the same brake line pressure due to larger MC area. A 23mm MC requires 1.47x more force for the same line pressure as a 19mm (needed if your calipers are unchanged during the swap). You also have 1.5x less travel.

Right. There's no free ride. The later 911's (at least most of the air cooled cars) with bigger brakes used a vacuum assisted brake booster.

Too big on the MC and you loose the ability to modulate the brakes. They become an on-off switch because you have to use your quads to force the pedal down instead of your smaller foot,ankle and calf muscles.