Cheap Thrills: Retrofitting an Eaton M90 Supercharger On An LS

With all of the junkyard talk these days, this test makes perfect sense. Richard Holdener decided to take a 4.8-liter LS engine and throw an Eaton M90 supercharger from the scrapyard. If you’re not familiar with the M90, these units were offered on the GM V6 3800. What makes this retrofit so appealing, if it works, is the cost of the supercharger or lack of. You can find these units on eBay for $175 on average. The only question is, will the V6 blower move enough air to feed the small cubic-inch V8 engine?

To answer this question, Holdener decided to hit the dyno and see what it could do. The first problem was figuring out how to adapt the V6 blower over to the LS. While one might think this would be pretty challenging, it wasn’t that tricky. For this test, Holdener used the lower portion of a Holley Hi-Ram intake manifold in conjunction with a custom plate he made. From there, the blower mounted on the plate after he measured to make sure belt alignment wouldn’t be a problem. Knowing that the supercharger might struggle at a high RPM, Holdener used a Brian Tooley Racing (BTR) camshaft to keep the revs lower with hopes of helping the blower do its job.

To get a baseline from the 4.8, Holdener made a naturally aspirated pull on the dyno. The LS produced 375 horsepower and 344 lb-ft of torque. While these numbers might not sound impressive, they’re not that bad, considering the mismatch between the BTR torque cam and the short runner intake manifold. With the baseline secured, it was time to put the M90 to work and see what it could muster.

When you see the engine on the dyno with the supercharger, it’s almost painful to watch. It’s like the two don’t get along, and it’s obvious. After we saw the dyno results, our suspicions were confirmed. This supercharger combination didn’t offer any significant gains. In fact, it lost power and a lot of it. Holdener states, “We didn’t so much put a blower on there as a restrictor.” The M90 made a dismal 1.2-pounds of boost down low and a falling boost curve after that. With the supercharger, the 4.8 dished out 314 horsepower and 297 lb-ft of torque. While we didn’t expect this combination to work very well in the beginning, we were surprised at how bad it did.

Since Holdener didn’t have any other pulleys to change to increase the boost levels, he decided to use nitrous instead. He installed a single nozzle system from Nitrous Express (NX) in hopes of making some power while on the dyno. Armed with a 52 nitrous jet and a 28 fuel jet, Holdener spun up the dyno. This time the supercharged combination did make some power, 442 horsepower, to be exact.

While Holdener didn’t dyno the 4.8 without the supercharger with nitrous, we’re willing to bet it would have made even more power. The problem is, the M90 is not a supercharger on the LS; it’s an air restrictive heat pump. So please, don’t waste your money on trying the combination. As Holdener shows us, you will be disappointed with the results, and remember, you get what you pay for. 

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About the author

Brian Havins

A gearhead for life, Brian is obsessed with all things fast. Banging gears, turning wrenches, and praying while spraying are just a few of his favorite things.
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