This may help:
Monday Mailbag: How to Calculate Brake Pedal Ratio and Master Cylinder Size - OnAllCylinders


8 to 1 is an aggressive ratio, "should" be more in the 5-7 to 1 ratio area. You may have a situation where the pedal is physically bottoming out on the floorboard but the MC's internal piston isn't near to bottoming out. I would say a 1" bore MC is a decent size to start with, but I only have dealt with a single MC applications.


Here is another link to brake info:
Master Cylinder FAQ
also click on their "tech support" banner, good info there. Hope this is helpful.

 

Your MC bore is most likely too small. As ranch said, the pedal is bottoming out before the MC can move enough fluid. According to this site:

Brake Technical Information

You should be running at least a 7/8" bore on the front.

The rear probably needs more volume and a 10 lb residual valve. The shoe return springs will pull the shoes back quite a ways from the drum without the residual valve. If you don't have a RV, this may be causing some of your problems. The MC has to move enough fluid to overcome the distance and a 3/4 bore isn't going to move a lot of fluid. Without knowing what the drums were from, I'm going to say they probably had at least a 7/8" bore MC operating them in whatever they were from. The drums are self-energizing, so with an 8 to1 ratio, you should be able to lock them up without any trouble.

 

I don't have a link to it right now on my phone, but on pirate4x4.com under the tech garage folder tab theres a bunch of tech articles by a guy named billavista. About half way down there's a brake Bible. His articles are geared towards off road use so the examples he give are for big one ton trucks calipers, but the formulas are the same.

He has an excel spreadsheet I believe where you can calculate pressures based off piston diameter and calculate the amount of brake torque needed based off weight, brake torque generated based off rotor diameter vs pressure, etc. If your interested in learning how it all plays together it's a useful resource. There are many other good articles such as the cooling bible, 12v DC article, tube bending, etc that can all be applied to hot rodding.

I used his brake spreadsheet when I upgraded the brakes on my off-road crawler, and also when I went to manual brakes on my Fairlane to verify I'd be able to stop it vs what I had with the power booster.

Sent from my XT1254 using Tapatalk

 

I'm using a 1" master on my '59 Ford with front discs and it stops fine. It probably would be less effort with a 7/8" master.


How close is the pedal to the floor when it stops? The rod from the pedal to the master may be too short.


For the pedal, I like a 7:1 ratio, my Ford is in the stock position.