E46Fanatics - View Single Post - Does a water pump fail more with age or mileage?
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Old 11-19-2012, 09:31 PM   #27
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Originally Posted by STiGLiTZ View Post
oh and FYI an under pulley kit causes the outer diameter of belt driven wheels to be reduced allowing FASTER spinning so combined with increased flow from the high flow bullet proof water pump i rest my case....not rocket science dude, now if you want to talk about that get out your crayons and yellow note pad so you can take notes
An under drive pulley, if it is actually under drive, would need to be larger diameter. This would reduce the tension applied to the belt and reduce the RPM of the part being turned. Less belt tension is less parasitic drag on the engine. If companies are selling "under drive" kits with smaller diameter pulleys, then they are doing exactly the opposite of reducing parasitic drag. Decreasing pulley size will increase the force required to turn the given pulley, and for any given RPM, the viscous (PSP or WP) or electromagnetic drag (for an alternator) would be increased. I think you might be the one who needs to take out your notebook.

Last edited by WDE46; 11-19-2012 at 09:32 PM.
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