Help with master cylinder size?

[CFster]

64 Dodge Polara 500 with:

Front: Wilwood 12.19" rotors with 4 piston fixed calipers - 4.80 sq in total bore size.

Rear: TSM 11.25" rotors with Eldorado single piston floating rear calipers - 3.23 sq in bore size.

I used this formula from Wilwood to determine the bore size:

"To determine the effective piston bore area of any caliper, you must first calculate the area for each piston bore found on one
side of the caliper. Use the formula " Area = ( bore x bore) x .785" for each piston bore size. Then, add the areas of all pistons
on that one side of the caliper to determine the total effective piston bore area."

I believe this means the rears have 67% as much bore size as the fronts - which somebody somewhere said was acceptable. 60%-75% I believe is ideal.



I'm running a Wilwood Master Cylinder with a 1.06" bore - manual brakes.

I'm also running a Wilwood adjustable proportioning valve.

I'm getting a pretty hard pedal - takes a lot of effort to get this thing stopped. With the prop valve opened all the way, I still can't lock the rears.

I understand that a smaller bore master will yield more pressure. Does anybody have any recommendations for size or type?

Thanks,
-Colin