As the title suggests I am wondering what benefits I will see from going to a larger brake master cylinder. I am currently running an unboosted dual circuit 120Y model but I am thinking of putting a larger one on.
Thanks in advance Matty

The upside?
A larger diameter piston will displace a greater amount of fluid for a given amount of pedal travel. This will be good if the pedal currently travels a bit far, even when the brake shoes are fully & correctly adjusted.

The downside?
You will generate less line pressure for a given amount of pedal pressure, so in order to restore the previous level of line pressure, you will need to press harder on the pedal.

If the resulting pedal pressure is still within acceptable limits, then it's all good,but if, after a while, your right leg looks like Arnie Shwartzeneger's & your left looks like a normal persons, then you just gotta know that you need a booster with the new cylinder.

if your brakes are otherwise stock, then i don't see much point in changing things

unless you just wanted to add a booster which will make it so you need to apply less foot/leg pressure

if you increase caliper or piston size, then usually you want to increase master cylinder diameter to compensate

Thanks guys.

I should have mentioned that I am running S13 Silvia front brakes and R31 Skyline rear brakes.

Matbighat - with the increase in caliper and piston size of my modified system will a bigger master cylinder allow increased braking force to be applied at the expense of extra effort on my behalf? Or, as Dodgeman has mentioned, will it just mean that the pedal doesn't travel as far?

Thanks again Matty

you can sorta get more line pressure, just have to push the pedsal further, as the smaller bore master cant go as far as the big one, you get more pressure
but you would have locked the brakes up by then

if your still using single piston calipers all round i doubt that you would need a bigger master, im running 4 piston front and drum rear(until the diff is done) and a 7/8th master, the pedal is like a rock....has about an inch or 2 travel, if you push really hard
but the car is pretty well on its way to being stationary by then

I have just upgraded my datto booster/master and have a spare Nissan DR30 81model Skyline booster set-up in A1 cond. this was pulled from the 4 weel disk model. Im sure it will need some minor mods for it to bolt up, but thats what datto's are all about MOD'S So If your interested PM me.

how bigs the skyline booster? would have thought it would be to big to use in a 1200

Its to big if your running a CA or SR, but with the good old A series there is room to spare. The guy i got it off rally's Datto's and he said the support on the back that bolts to the flywall needs to be shortened slightly to allow clearence of the strut tower.

you get bigger calf muscles if it's your daily driver.

yes, yes you do