So something a little different with the usual turbo modifications is that I realized the limitations where what after market compressor wheel was available for a specific wheel when there are so many that are used in other makes and models. Not to mention the cost of say an HE1 Holset wheel can be used in the larger TD04 housings. Certain Schwitzer wheels that are a bit larger and extended fit in some of the Garrett housings even sometimes fitting the shaft id. This of course not without some if not a decent amount of modifications to the backing plate, sleeving the shaft, and modifying the compressor housing in a few ways to make all the tolerances just right. Yes, in certain models like the above Garrett, I modify the housing as well to avoid choking. You can read more at this link.
The video on the right is a test on my Turbo SV650s where we finally got some numbers 109.50 HP and 63ftlbs of torque from a stock engine.
As to the Super Mod turbo's, some of the other improvements of course comes from the bushing material alloy that C39800 or 700 that has a higher heat tolerance with some self lubrication properties to the alloy making it ideal. Also in the way in which we machine the bushings alow for better flow especially guys and gals running thicker racing oils.
I have two blogs on turbos so here is the other one. At that sight you can get pricing on general turbo rebuilding services and some of the do's and don'ts that are common when putting a system together. This side business has become much more and a bit of fun at that.