I may be a bit naive here, but how is adiabatic efficiency going to be met under the hood of a car? I really don't see that happening. I know I could be mistaken here . . . wouldn't be the first time.
I really don't know how to answer that question. I understand that the m90's are about 65% efficient at about 14-15k rpms. Turning up the rpms that percentage will start to drop. Hopefully someone more knowledgeable than me will chime in and answer that for you.
I would like to add that I don't recommend what im going to try to anyone. One needs to make many other adjustments or mods FIRST.
The first thing one has to do is make sure they have a free flowing engine, and control your ACT/IAT's, then will it be ok to try and start spinning the m90 faster. I have already made my motor as free flowing as it prob will ever get.... I have PnP heads, over sized valves, big bore, cams, gasket matched intake runners, headers, no cats, 2.5'' true dual through an X pipe, free flowing flowmaster super 40 mufflers.
Next step is to get your ACT/IAT down as much as possible. Because when the air starts to stack up, it will start to create more heat. Boost/psi is not a good thing, the less boost you see on your gauge the better. Less boost means a better flowing motor, air that is being pumped in the motor is going out faster. When the air can't leave the engine fast enough, boost pressure rises, heat rises, timing drops and you lose power. Once you reach that point you will make more power by turning less rpms on the blower.
I have also gone as far as prob more than doubling my intercooler water capacity and I have taken some pretty radical measures to lower my ACT/IAT's. I plumbed a volks golf H/E all the way at the back of my suv under the car angled so it gets great airflow, it also has a 12'' fan blowing air through it. Then I made a ice box with exposed copper tubes so I can fill it with ice on race days. I will be changing the copper tubes to the best sized AC evaporator I can fit in the box to transfer even more heat. I might go as far as plumbing two AC ducts into the lid of the ice box to chill the copper tubes or evaporator. I can have the AC blasting on it while I line up for the light.... When im driving around town I always have my AC on so that evaperator will be chilled normally, if I go WOT, AC turns off from EEC and the evap will be cool enough for a nice blast. I have two roof AC vents way at the back in my 3rd row seat. I can easly plumb some tubes from my roof to the ice box lid. I might even wrap my inlet intake steel tube thats between my MAF and TB with an AC line, and practically be able to freeze that tube.
I have a functional hood scoop and I can literally see my SC water temps cooler driving around town (I have a water temp gauge for my intercooler water, two of them, one for inlet and outlet). The air flow going through the scoop is literally hitting exactly on top of the plenum. I have also removed my front and rear rubber seals that seal off the engine compartment. I get GREAT airflow to my motor. I'm doing a little research now before I take this other step, but I might add 100% distilled water for my intercooler with Water Wetter and a anti-corrosion solution.
I also have a custom cold air system that is sucking the fresh air into my air filter box.
And to top it all off I am spraying meth/water with a Snow Performance kit.
So as you can see I have gone through some pretty drastic measures to control the negative bi products of spinning an m90 that fast. I wouldn't attempt to spin the m90 that high if I didn't already have all this in line. I have already maximized my motor flow, maximized ACT/IAT temps.
its time to maximize the blower and see what I can squeeze and accomplish before the diminishing returns.
I think I will have very favorable results.