Just so you don't get to waist thousands of dollars like I just did selecting the wrong turbos wanting to build a DIY Gas Turbine, I've put together an Exel spreadsheet in which you can input the turbo manufacturer specific turbo specifications such as the compressor inducer diameter, the compressor exducer diameter, the turbine wheel inducer diameter and the turbine wheel trim.
Just put the right numbers at the right place and look at the percentage (%) at the end. If it's not between 8% (My proven DIY turbines using GT4708R) and John's recommended "Around 25%", you might not want to buy or waist the time on that perticular turbo.
Looking at the bottom of the document, you will note two tabs, one named "Turbo Tech" which explains what is the "Trim" in a turbo and the other tab is the calculator sheet, and in which you just have to fill the "Green" cells, DON'T touch the "Yellow" cells and keep an eye on the "Light Blue" cells ...
See the attached, hopping I have contributed you don't waist a bundle like I just did
Moderators, you might want to make this one "Sticky" ...
Cheers