I'd like to see what kind of tolerances they're made to, and if spun fast enough, will they actually produce air pressure above atmospheric. At some point, I'm going to take a RB Supercharger and modify it to actually produce some air pressure and test it out on a small aircraft 4-stroke. I have a .46ci that would be a good test subject. A turbo would be even better on a 4-stroke, but making a working turbo that small requires some very tight tolerances and very intricate machining processes.