some m90 questions

SlickSix311

Registered User
i will be purchasing a used m90 supercharger for a custom project on my mx6 and i have some questions.

1.) is there any certain year/generation of the m90 i should stay away from due to reliabilty, etc. problems?

2.) do all the generations of the m90 include a bypass valve...if not which ones do?

3.) does the bypass valve allow for no or very low boost in cruising conditions? (not accelerating)

4.) how exciting do low 14's/high 13's at 6lbs of boost sound?
 
1. They are all built like tanks. Very reliable and can go 200,000 + miles. They can be rebuilt for around $300 by several sources.

2. 89-93 have an oval shaped inlet. The 94-95 have a rectangular shaped inlet that is larger and the rotors are coated with teflon to reduce clearances. The 94-95 M-90 is much more efficient than the earlier generations because of this.

3. You are correct on the by-pass valve function. It allows the car to run in vacuum under normal conditions.

4. The M-90 is actually most efficient at around 8lbs. of boost.

If you are only going to run 6lbs. of boost an 89-93 M-90 should do you just fine. It will be much cheaper to buy than a 94-95 model because of the improvements. Just be careful when you set your final drive ratios for the supercharger so that you don't overboost your engine past the 6lbs. that you want. The M-90 on a stock SC pushes about 12lbs. of boost. My 90 SC has a 10%+ pulley and it hits 15 lbs. and my 95 SC has a stock pulley and hits 15 lbs.

Hope this helps.

Bob
 
take a look at the Bonneville(GM M62s and M90s) blowers, they have internal bypasses in the supercharger case instead of at the plenums(more compact). If size does matter:D
 
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