I recently rebuilt an Eaton M90 supercharger for a project engine, and a reader suggested I chronicle the process. For starters, I found lots of good information online but ran into a few problems that no one seemed to mention. Sources like Rolling Performance and Thunderbird Infoway served me well for both details and parts, but I’ve since located an even better source for rebuilt kits. More on that later.
The first thing you need to do is locate the supercharger itself. Mine was a decent eBay find selected more for the $90 price tag than for apparent quality. It’s in decent shape, but 170,000 miles is hard on any component. New or freshly-rebuilt M90s cost anywhere from $300 to $600, usually with a core charge tacked on if you don’t have an old blower.
There are two problems with my blower that you should watch out for. First, scoring in the housing. Small particles, despite the air filter, can get in and tear minute scratches in the wall, which reduces the ‘charger’s efficiency. The only fix is a new housing, which is a little rich for me right now. Second, a damaged pulley left over from a botched removal attempt by the shop I bought it from. If you’re using an M90 as a stock replacement, that’s a big issue, but my plans called for an aftermarket interchangeable pulley system anyway.
As far as junkyard sources go, you can pull M90s from Buick Park Avenues, Pontiac Grand Am GTPs, Jaguar XJSs and XJ6s, Ford Thunderbirds, Mercury Cougars, and probably a few more I don’t know about. None of these are uncommon vehicles, but you should look for one with its intake tract unmolested, which should give good odds of finding a clean Roots-type inside. Pulling them is pretty simple, but keep an eye on the snout lengths. The distance from the case seam nearest the pulley and the outermost face of the pulley varies from car to car, and may affect fitment in your application. To my knowledge, Cougar/Thunderbird snouts are longest, and Grand Am GTP snouts are shortest. There are also several intake and pressure flange designs, just to make life interesting.
Stay tuned for part two later this week.