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Old 02-07-2007, 02:23 AM   #4
330DTM
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Okay I did some research on some old threads from B/F. Here's some insight from what I've gathered:
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carcrazed: You're correct to an extent. The entire means by which an underdrive pulley works is an increased pulley diameter and to some degree lightening of the pulley.

Specifically, the UUC pulley changes the diameter of the of the power steering pulley and water pump pulley, but not the alternator pulley (its weight is simply reduced).

That said, you can't use the UUC pulleys with the AA S/C. Even though the S/C is crank driven, the different belt length(s) required by the UUC pulleys increases the operating RPM's of the AA S/C at any given engine speed. As such, the AA S/C will spin beyond it's maximum warrantyable speed, causing several issues:

1. Your S/C's warranty will be void.
2. Your S/C will likely fail, if not right a way, much sooner than a normal lifespan.
3. Your engine will be damaged since the AA software doesn't account for the additional boost produced by the S/C in these conditions. It's likely you could kill it altogether.

In short, the UUC pulleys ARE NOT a good idea with the AA S/C. They'd be fine IF AA used a different S/C capable of the higher RPM's and accounted for the extra boost with software, but they do not.

In any case, there's not a significant amount of power to be gained with the pulleys. I guess you guys will just have to save the $185 and "suffer" with 5-9whp less.
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Source: http://forums.bimmerforums.com/forum...ghlight=rotrex
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