Revisiting the underdrive pully topic for fresh info.

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Don't overthink the pulley. It does improve the life of PS pumps and probably alternators as well on cars that spend a lot of time in high rpm. Remember that the smaller the pulley, the slower the water pump turns so there are practical limits. It does lessen the parasitic loss from running the accessories but dyno results from the Boxster spec series looked like it was in the 3-5hp range. Finding a real 12hp with an UD pulley is the stuff of fantasy. A well balanced pulley is probably far more important than getting the absolute smallest.