How-I-Did-It: 2.8" Pulley Change
Posted April 17, '02

Pulley Change on Stage 3/360R/380R/Classic

Why change the pulley on your supercharger? The easiest answer: instant boost increase.

The Roush Stage 3, 360R/380R, and Classic come stock with an Eaton M90 Gen 4 supercharger with a 3" pulley (approximate size - actually 78mm over gage). The 3" pulley assists the supercharger in producing about 6 pounds of boost under wide open throttle. This is the result of the engine turning the supercharger at a certain RPM.

When the supercharger is turned faster, more boost is produced. By putting on a smaller pulley, the supercharger turns faster, thus producing more boost.

This pulley I am using (which can be purchased from the Marc) is approximately 2.8", machined from billet aluminum, and coated black. The quality seems to be quite high, with no visible flaws in the pulley I received. After installation, I found my boost gauge enjoying boost levels of at least 8 pounds, and possibly 9 pounds. While I have not had this on the dyno yet, the car feels a bit more responsive than before.

This is the first aftermarket pulley I know that was made to work with the Roush supercharger setup. It has not been tested as thoroughly as the stock pulley, so if you are to do this modification, you are probably on your own if there is an engine failure. With the fine engineering of Roush with this supercharger along with the Powertrain Control Module ("the computer"), I am confident that my engine will experience the same longevity as non-modified ones.

Understand that I am in no way providing any quantitative data supporting this modification will give a certain amount of horsepower or will not cause engine problems. Please assume all risk of modifying your car!

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Preparation:

Workspace: A well lit area that allows you to work under the hood.
Tools: Ratchet and 18mm socket to remove stock pulley, 1/2" ratchet for idler pulley, rubber mallet, shop towel, optional channel locks.
Parts: One 2.8" pulley.
Left-over Parts: Stock pulley.

Quick Instructions:

1. Getting started
2. Remove the Stock Pulley
3. Remove Supercharger Belt
4. Remove Stock Pulley
5. Install New Pulley
6. Replace Belt
7. Finish up

Procedure:
Note: Some full-sized images have additional information, arrows, etc.

(Click thumbnail for full-sized image)
Getting Started Set the parking brake on the car and put car in gear. It will help if the engine is cool, as you will need to touch several parts while doing this change.
Remove the Stock Pulley To remove the stock pulley, use an 18mm socket with a large-handled ratchet (1/2" works fine). Use a shop towel to help get a grip on the pulley and belt. The belt will help add resistance, and with the car in gear, the engine will also assist in holding the pulley while using the ratchet to loosen the retaining nut. Remove nut from shaft
If the pulley turns while trying to remove the retaining nut, you can try to carefully use some channel locks to hold the pulley. Note: Be very careful not to damage the belt or stock pulley when using something to clamp onto the stock pulley. My pulley came off without the use of channel locks.
Remove Supercharger Belt To remove the belt, apply pressure to the idler pulley by inserting a 1/2" ratchet into the square opening and pushing down on the ratchet handle. This will put enough slack into the belt to allow you to slip it off the supercharger pulley.
Remove Stock Pulley Use a rubber mallet to carefully remove the stock pulley. Give the pulley a few taps, rotate, tap some more. Continue to tap and rotate until the pulley comes free from the shaft.
Install New Pulley Some anti-seize compound may be applied to the shaft at this time to prevent dis-similar metal oxidation. The original pulley is steel, and the new pulley is aluminum. The shaft on the supercharger has a key that lines up to the keyway in the pulley. Check the orientation of the pulley and slide it onto the supercharger shaft. Not in the picture that there is a specific orientation the pulley must be in to enable it to work properly. Reinstall nut onto supercharger shaft.
Replace Belt Once again apply pressure to the idler pulley and slip the belt over the supercharger pulley. Tighten the nut using a technique similar to the one used to remove the pulley. Nut will not go as far onto the shaft as with the stock pulley.
Finishing Up Make sure the nut is tight on the supercharger shaft. Put your tools away and take her out for a spin!

Its Done!

This is a very easy replacement for quite a bit of SOTP enhancement! I noticed at least 8 pounds of boost while driving after replacing the pulley. The highest I had seen on the stock pulley was 6 pounds.

Dyno results to come soon!

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