DIY - Brake pedal ratio?

Anyone know how to determine brake pedal ratio for pressure output? Or know what it would be on 1949 Pontiac?

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I have always had good luck finding an original example with the same master cylinder and then measuring the distance between the pivot of the pedal and the pedal pad, and then the pivot of the pedal and the push rod then converting that to a ratio. I am then able to adjust the length of the pedal assembly to suit me and still get the same feel. now that being said if you use different size slave cylinders than what the original master cylinder was designed for you have added another variable that will have to be dealt with. If the new slaves are larger you with need a higher ratio (say 6:1)for the same feel, if the slaves are smaller you will need a lower ratio(say 3.5:1) to produce the same feel. At some point you will just have to make an educated guess or make your pedal assembly adjustable.

 

http://www.stoptech.com/docs/media-center-documents/the-physics-of-braking-systems

 

I have been talking with Willwood about upgrading stock MC and they asked for bore size and pedal ratio. I know I will probably have to make pedal adjustable to get whatever I do to work properly.

I have 3 plans in head not sure what want to do.

A. Use smaller size remote fill master from willwood in stock under floor location with fabbed bracket

B. Under dash right angle 90 degree pedal assembly with vette style master or willwood and remote fill if needed

C. Mount vette style master on firewall with new 57 Chevy brake pedal assembly (this requires removing stock heater box from firewall where master needs to go and under seat heater that attaches to that core)

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Generally speaking;

Power booster? 5 or 6 to 1 ratio.

Manual brakes? 6 or 7 to 1 ratio.

 

Sticking with manual brakes. Currently drum/drum but want to do disc/drum but stay non-power.

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And the bigger the master cylinder bore the harder it is to push it.

 

7:1

 

6:1

 

Here's one I made for my Henry J. 6 to 1 ratio with a 7/8 bore master.

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Blue

 

So thinking if it is 7:1 use 1" bore. If 6:1 use 7/8" bore. Either way nothing is going to be a bolt on application need to redesign something and adjust, adjust and adjust. unless I just say screw it and leave everything stock.

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