Basically, the M62 is roughly equal to a T3-60 trim turbocharger. The M90 is roughly equal to a T04B S-trim turbocharger-but limited to about 12lbs of boost in both cases. Horses for courses. I don't need super-high HP in a truck, but I do like bulk low-RPM torque.
The truck only needs to turn 5000RPM, ever. It's not a race car, but I do use it to haul engine parts/drag cars/general abuse so low-end torque is nice to have. I may use an M90 just because I have 6 on the shelf, but I only have one M62 and it's the long-case version that won't package well. Also, it's got a T-5 transmission in it, and they're only good for about 300ft-lbs before they shatter.
The reason the 3800SC guys are running then out of their efficiency is that they're getting power greedy. The eatons on those engines aren't designed to run at 6000 engine RPM, they were designed to give bulk torque and the sensation of speed and power at 3000RPM, which is where they're still efficient. Significant case reconfiguration is needed to get serious performance out of the GM blowers. The Ford, Jaguar, and Mercedes blowers are a lot better in this regard.
By changing the shape of the case, I was able to go from 600CFM inlet flow, to just over 800CFM, before hitting the limit of the compressor on this M90. Raised inlet 2.4", opened from 65mm to 88mm.
Also made it fit much better in the engine bay. Shortened the nose up to M62-length too, to fit the accessory drive.
That said, if I knew I had the usage of the 2-bar MAP sensor, I'd just chuck a small turbo on it and call it a day. Might hunt down some Syclone badges or something, that'd be pretty awesome.
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