3/4" master cylinder?

i don't know how you are measuring pressure at a length of 14"? Not mentioned but i had a problem stopping with new front disc brakes..it was scary. It wasn't a pressure problem but "bedding in" issue. I ended up taking the car out on a quiet highway and hauling it down as best i could "hard" from about 50mph 3 times. then after they cooled some gentle stops from about 30mph. Brakes grabbed and it stopped nicely from that point on. You should have more than enough pressure even with a 7/8" master.