And yes, you're probably right, it looks like a March pulley. I use to run one myself. 
What is this part??? (with pictures)
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Launching!
Joined: Jan 2010
Posts: 236
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From: Warrenton, VA
What is this part??? (with pictures) I have a 94 firebird formula. What is this? I found it in the back of my car. It looks fairly new I thought it was an underdrive pulley. Is that true? Is it stock?
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Launching!
Joined: Apr 2008
Posts: 203
Likes: 1
From: Townsend, DE
The Under drive Pulley slows down the accessoires (Power Steering, A/C, and the alternator) SInce the alternator is spinning slower it wont charge as good as stock. no big deal unles you have a big stereao that demands a lot of power. They do make a pulley for the alternator to compensate for the underdrive. I cant remember how much shorter the belt is. sorry..
The length is hit or miss unless you buy the kit. You can purchase one, such as the_merv did, and then swap it if it is too long/short.
The alternator pulley is a smaller pulley to make the alternator spin faster, is called an overdrive pulley, and I had to run one on mine. The battery died while idling at the track b/f I installed it, so I put it on and it was all good. All stock electrics, btw.
When I had the UD pulley and no OD pulley, I used NAPA part number 25-060598, which NAPA says is 60.4"
When I put the OD pulley on the alternator, I used DAYCO part number 5060590, which is a 59" belt.
The alternator pulley is a smaller pulley to make the alternator spin faster, is called an overdrive pulley, and I had to run one on mine. The battery died while idling at the track b/f I installed it, so I put it on and it was all good. All stock electrics, btw.
When I had the UD pulley and no OD pulley, I used NAPA part number 25-060598, which NAPA says is 60.4"
When I put the OD pulley on the alternator, I used DAYCO part number 5060590, which is a 59" belt.
March recommends a 590 belt, however it is still a tad long so the pulley tensioner is not used effectively. If the A/C is still operational the belt may squeak for a few seconds after the compressor is engaged. If you use the U/D pulley it would be a good idea to use an alternator O/D pulley.
