You'll get a lesser mechanical advantage by using larger master cylinder.... Pressure=Force/Area.
ie/ More work req'd by you.

As you've increased the diameter of your brake pistons by a fair bit by going to the Silvia / R31 brakes, you're already getting a heap more mechanical advantage than stock.

with that in mind, I reckon a slight increase in your M/C size wouldn't hurt.

But - As any tradesman will tell you.... If it aint broke, don't fix it

i'm running a 13/16 sunny, with twin sumi's and R31 rear, very hard pedal and only about 10mm
pedal travel

Thankyou for all the responses.

There has always been a fair bit of pedal travel which has never worried me as the car pulls up very well.

Would I see a reduction in braking distance by fitting a 240Z 13/16 master cylinder?
Matty

240z master is 7/8ths, yes you would see a reduction, you will have about an inch of travel
id try maybe a 120y 3/4 or sunny 13/16ths, even the 13/16ths might be a bit much

but they are only about $80 brand new so its not exactly a huge loss

Quote:

yes, but you'll need to experiment. don't go too much larger than what you're running now unless the pedal is still too soft for your liking

Thanks Pigdog and Matbighat.

My current 120Y one is 11/16". If I go to a 13/16" that will be an increase of 16%. Does anyone see an issue with an increase of this size straight up?
Thanks Matty

Pigdog - where have you bought master cylinders for $80 from?
Thanks Matty

using the large sunny MC with wilwoods ;) very nice pedal feel!

i get my mastercylinders from my local brake place, if you cant find any that cheap let us know and i can get one for you, only be like $10 to post

Thanks Pigdog.