Boosters This is the most common way to gain pressure. A power brake booster is like a stereo amp. It takes the the signal coming in and amplifies it on the output side. Bigger Boosters are like bigger amps, - more power.
The other key item is vacuum. Gotta have some. We use 18" as a test standard. Over the years we have tested a lot of boosters, and of coarse, we gathered all of the info. So, it's kinda like this:
For a givin size of a booster, you can have an approximate multiplier, based on 18" vacuum. This multiplier can be factered into the line pressure calculation.
A 7" single diaphram booster has a 1.7 to 1 multiplier
7" dual diaphram = 1.95 to 1
8" single = 1.9 to 1
8" dual = 2.25 to 1
9" single = 2.15 to 1
11" single = 2.45 to 1
Now these are averages from years of collecting data. **your results may vary**
If we go back to our example, at 267 psi. and add an 8" dual diaphram booster (267 x 2.25) we can expect to get 600 lbs of line pressure, givin 30 lbs of foot pressure on the pedal, and 18" af vacuum.
With this information, you can figure out the results of changing ratio's, boosters, and bore size.