I need a small master cylinder with 7/8" bore

Doosterfy said
That's good helpful info. I will try to locate the tool to measure the actual clamping pressure exerted by the calipers. About the 7/8 bore not having enough volume to fill all those pistons at the calipers; Wilwood recommended going to the 7/8 bore to get more pressure to the calipers with less pedal effort. If I did have a case of not enough volume would it not show up with a very low pedal? My pedal goes down about half way and is no where near bottoming on the floor. I will try swapping the lines so the rear piston powers the fronts and vice versa, that will be very easy to do. Now the hydroboost. Heres why I think it would help a lot; when testing with the pressure gauge I'm getting 1000 psi with normal firm pressure on the pedal. I also got it to 1300 with very high pedal effort and when I road test it I can lock the wheels with the same very high pedal effort. My thinking with the hydroboost is that I would be able to get the higher pressure to the calipers without having to exert very high effort on the pedal. Vacuum boost is not an option because the cam is too big so I only have 5hg of vacuum. Thanks for the input.

You have to remember that a booster of any kind is operating outside of the hydraulic braking system. It essentially is like just giving you a heavier foot to push the pedal. It's not changing the amount of hydraulic pressure being made by the master cylinder. Again I go back to what matters is the amount of force applied to the pads/rotor vs the amount of pedal travel.
To answer your other question about whether too small of a M/C piston would make the pedal low, I'm going to assume you mean it travels farther toward the floor, yes a smaller bore would increase the travel and make it closer to the floor but you would still feel a firm pedal as long as it were bled correctly and there were no air in the system. However there is a certain amount of limitation to the smaller M/C's leverage, if you will, so you would get to a point where your foot would feel a hard pedal but you wouldn't be able to make enough pressure. As the pressure you do make increases the more difficult it becomes to continue to increase it more. It goes back to the ratio of the M/C vs the Caliper piston.
I hope this is helpful & that I'm not confusing in my explanation. Please post what happens with the changes as you go. Good luck! -LW