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Old 11-21-2012, 05:07 AM   #37
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Join Date: Jul 2012
Location: Liverpool
Posts: 1,523
My Ride: 320i SE Coupe
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
Surely, an underdrive pulley is considered to be an accessory pulley that is LARGER than the stock pulley. (Wiki. Never heard the term personally) In other words, the belt has to travel further in order to turn the pulley through 360 degrees (1 rev). For any given belt linear velocity you would expect fewer revs of the pulley for each belt cycle than with the stock pulley ie: reduced RPM. Since the pump shaft is rigid, not geared, this would result in fewer revs of the vane inside the pump that is responsible for moving the coolant. Reducing flow. Not incresing flow. Yes?

Last edited by RayPooley; 11-21-2012 at 05:45 AM. Reason: corrected "... stock belt" to "... stock pulley"
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