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Discussion Starter #1 (Edited)
New products for the 2.2 and 2.4 Engines:

MRZ Performance lightweight and undersized pulleys (UDP).

I installed the MRZ UDP pulley on my 2.4 -- feels more responsive at part throttle. It slows down the speed of the alternator and AC compressor about 10%. I can't tell any difference in the engine vibrations either.

MRZ Undersized Pulley, New Balancer Bolt (GM PN11589123), and Shorter drive belt (ACDelco 5K390). The long tool is for the belt tensioner -- but it didn't work, no matter where I connected it to the tensioner I couldn't move it enough to get the belt off. Ended up using a bar and jack to lift the tensioner:


http://www.yourcobalt.com/photoplog/index.php?n=338

In this picture you can see the Pulley and shorter belt installed. The lines indicate the torqueing of the bolt - torque to 74 lbs ft and then an additional 75 degrees (NOTE: Factory torque for the balancer bolt is 74 lbs ft and 125 degrees -- MRZ pulley is aluminum and their torque requirement is lower. Just want to make sure no one uses this information to torque a factory bolt on the factory balancer incorrectly!):


http://www.yourcobalt.com/photoplog/index.php?n=339

The MRZ Pulley comes with installation instructions and is fairly easy (at least if you've done engine work before).
 

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Discussion Starter #3
Yea at $174 they are not cheap...But remember it is not a mass produced part. Maybe as more are sold MRZ can bring down the price. It's all about making parts, getting people to buy them, and making some money. The more they sell, the less they can charge. The more money they make the more inclined they are to make more new parts for our cars. I don't make the rules....and I don't mind getting new parts for my Cobalt if they work...LoL!!!!!
 

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Discussion Starter #5
looks good.

but i got a lightweight crank pulley from z-spec for $100

been on for 2 years and no problems or complaints as of yet
I had never heard of Z-spec until your post. Is it the original size as the factory pulley? I went with the MRZ UDP to slow the alternator and AC Compressor about 10%. I haven't had any problems, completed a 150 mile round trip and got the highest fuel mileage I've recorded with my 2.4L 33+ MPG.
 

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Good question. I am interested as well, but my a/c will freeze you out of the car. If I lost 10% performance in my a/c, it would not be a big deal.
Same question from me, how does it affect the a/c??
 

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Discussion Starter #9 (Edited)
I have not noticed any difference in the AC at all. When I say it slows it down 10% think of it this way: At 2000 engine RPM your AC compressor is at >4000 RPM. With the UDP the AC compressor "slows" to >3600 RPM -- more than enough to keep your AC system running. The Alternator has an even smaller pulley and spins REALLY fast (something like 2000 engine RPM = 5400 alternator RPM, with UDP 4860 alternator RPM)! I had the voltage and amperage checked at Autozone before and after the MRZ UDP install -- at idle and 2000 RPM the voltage and amperage was the same.
 

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Great information. Thank you. My future mods list may be growing soon!
 
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