Originally Posted by
Michael
The way I understand it, there are two reason not to overspin an SN:
1. Above 40,000 RPM (approx.) is beyond the impeller/scroll design's efficiency, so very little boost gets generated beyond that point.
2. Significantly increased levels of heat is developed beyond 40,000 RPM.
Heat is what breaks down the ATF fluid within the SN which is what ultimately leads to the bearing races/balls being damaged. And from everything I've read, heat breaks down ATF very quickly, so the more heat that's generated, the faster the fluid breaks down. That's the reason so many people run an external cooler on their SNs.
I don't think it's both RPM and boost that causes the damage, since the SN's pretty much max' out at about 5-6psi. I think it has more to do with over revving (in search of more boost) and not replacing the fluid on a more frequent basis.
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