Single vs Dual Circuit Proportioning Valve

[neongreen]

Here's my setup. 1962 Falcon with Mustang II front suspension. this includes 11" front rotors with 2.75" single piston floating calipers, and 10.5" rear rotors with 2.375" single piston floating calipers. The brake booster is an electric Bosch iBooster and a 26mm (1.02") master cylinder. I think just based on the math the bias ratio is 1.34:1.

This is a new master cylinder setup. I was using a pedal assembly from wilwood with dual masters and balance bar. I did not like the brake feel, and to keep the rears from locking first under heavy braking, I had to adjust the balance bar to it's extreme. Also I've never been able to get the fronts to lock. So I've designed and built a new pedal assembly with the Bosch iBooster as it is very compact.

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Since this is a frankenstein setup, I'm assuming a proportioning valve would probably be a good idea. However, I can't find any good info on why I would choose a dual input/ouput prop valve vs a single input/output. What is the difference in function between the two desigs?

[dontlifttoshift]

Packaging is the only reason for a dual input prop valve as it allows an easy split for the front lines. Just run the standard wilwood or equivalent single in/ single out prop valve.

You are definitely going to want a prop valve but I am not sure you will ever get to where you need to be with those calipers. Piston area as you are currently set up based on you numbers.

Front 5.94"
Rear 4.43"

You likely have too much rear brake, with those front calipers I would think rear piston area around 3.5" would be about right.

The other issue you will have is the volume requirements for all of that area is going to require a larger master cylinder than 1". For comparison, a ZO6 corvette has a total area for all four calipers of about 13" (off the top of my head) and you have 20.74" squared........about 60% more than a Corvette that also uses a 1" bore master cylinder. Couple that with the large amount of assist that comes from the iBooster and you are going to have a very spongy pedal with a large amount of travel.

[neongreen]

Thanks for the feedback. I'll do some thinking and research on the sizing. As a rule of thumb, is 1.7:1 a good area ratio (from the numbers you provided) for front to rear assuming similar rotor sizes?