master cylinder for stock front disc + empi rear discs

[mabbo]

hey dude.

thanks for that. how does that calculation work with twin or 4 piston calipers compared to single sliders?

i have just worked this out but i dunno if its right as the front calipers are 2 piston, and the rears single piston:

944 master cylinder:
40/23 = 36/19
1.74 = 1.89

bug master cylinder:
40/19 = 36/19
2.11 = 1.89

my maths is rubbish, i dunno how to change that to a ratio :S

mabbo

[evilC]

Originally Posted by mabbo

hey dude.

thanks for that. how does that calculation work with twin or 4 piston calipers compared to single sliders?

i have just worked this out but i dunno if its right as the front calipers are 2 piston, and the rears single piston:

944 master cylinder:
40/23 = 36/19
1.74 = 1.89

bug master cylinder:
40/19 = 36/19
2.11 = 1.89

my maths is rubbish, i dunno how to change that to a ratio :S

mabbo

The calculation requires the TOTAL piston area for the caliper(s) it will therefore take care of the single pot, 2, 4, 6 or even 8 pot calipers, even those with different sized pistons in the same caliper.

Your maths is rubbish You have factored in the diameter not the area . you can discount pi in the calculation as it is a comparison and features on both sides of the equation therefore your comparison should read:

944 master cylinder
4 (2 pistons each side) x 1600 (40 squared)/529 (23 squared) = 12.10
2 (1 piston each side) x 1296 (36 squared)/361 (19 squared) = 7.18
Therefore the front rear ratio is 12.1/7.18:1
i.e 1.69:1

bug m/c
4 x 1600/361 = 17.7
12 x 296/361 = 7.18
Therefore the ratio is 17.7/7.18:1
i.e. 2.47:1

Joe Amato's figures are wrong insofar as they don't take into account the total piston area of the caliper. The hydraulic fluid is acting on both pistons simultaneously of a 2 pot caliper

evilC

[mabbo]

dude

cheers for that

so, what sort of ratio should i be aiming for?

would you just stick with the stock bug master cylinder?

its a street car, there are loadsa people using the empi kit with stock master cylinder id imagine - the bias must be acceptable?
if the reason my pedal was 2 soft wasnt because of the 19mm bore (im sure it wasnt), it must have been because of a faulty master cylinder...

mabbo