I didn't plot the barra on either compressor map so it is entirely possible that the initial pressure ratios were incorrectly assumed to be necessary.
Pressure ratio is defined as absolute inlet pressure divided by absolute outlet pressure.
The math is simple; gauge pressure plus atmospheric pressure divided by atmospheric pressure.
Atmospheric pressure at my house is 14.65 psi according to my barometer. It actually varies a bit
To calculate the boost needed to run a pressure ratio of 4 in the bw you calculate it like this; 4 multiplied by 14.65 then subtract 14.65 from that number. It's 43.95.
When we talk about comp wheel size we commonly refer to the inducer.
The bw compressor has a 67.7mm inducer vs the 76mm in the gtx. That is a significant difference.
The gtx flows approx 110lbs/m at 109,000 rpm vs the bw needing approx 116,000 rpm to make 95lbs.
I'll post up a link shortly that will help.