Before anyone yells at me, I read through like 9 posts I found using search, and nothing yielded an answer to my question. I recently bought Unothodox Underdrive Pulley's for my car. We were replacing my clutch, and my friend told me I might as well get them now while the car is all apart. This was before I found this forum and found that they would give me poor alternator performance. I thought about selling them on ebay, but fear that no one would buy them and I would lose out on the price of the part plus ebay fees, and I am putting my car together this week. So, on to my actual question....why are they different sizes, and will I need a new belt? I could assume they would be different sizes to be able to spin the crank pulley more, while adding that stress to the alternator, but have no idea as to whether or not I will need a new belt. I have a 2004 Civic Si Hatch in case that is needed. Thank you.

 

It's not really the alternator pulley that people worry about. Unless you have a stereo system or other components draining the battery than you might have an issue. The alternator will still charge the battery just not aswell because when you are idle it will not generate power. The Unorthodox pulley set also replaces the crank pulley. Which some people believe will add more stress on the engine because OEM honda pulleys have a harmonic dampener to keep everything in rhythm so to speak. But Unorthodox claims that their pulley set is 100% fine.

Some people wont do it because of this reason. But I have yet to read or see a engine go because of AEM or Unorthodox pulleys. Since you have them I would put them on and if you feel like your haveing some problems take them off. Thats my .02 cents.

The belt should come with the set if it needs one. I would go to their site they should show what you need for that model, or just ask them.

I would read this post for more info https://www.hondacivicforum.com/m_242734/tm.htm

 

dito.... the alternator is usualy the main problem because it spins the alternator slower....
but as long as you dont have your stereo pumping with your headlights ON just idling you probably would never notice a issue.
in my case i want a overdrive pulley for my alternator.... these alternators already suck at only about 70amps. hell my amplifier alone can pull that much juice. [:@]

 

I'm not even running that much of an amp and my headlights flicker pretty bad at an idle.[&o]