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Overdrive vs Underdrive Performance Pulleys

5K views 1 reply 1 participant last post by  AutoGuide.com 
#1 · (Edited by Moderator)
Overdrive pulleys are for the S/C, while Underdrive pulleys are for the N/A cars.

Overdrive pulleys spin the supercharger faster for a given engine RPM to increase the boost level.

Underdrive pulleys consist of alternator, water pump, and crankshaft pulleys to spin the accessories slower for a given engine RPM. You retain the factory belt.

Some underdrive pulley are a "piggyback" style that bolts to the factory harmonic balancer; others replace it entirely.

The idea with underdrive pulleys is that by lowering the speed of the accessories, you reduce the parasitic loads on the engine to free up driving power. The reality is that these gains are miniscule and can lead to underperforming electrical systems at lower RPM, especially with additional aftermarket electrical loads. However, the power steering pumps on these cars do not tolerate high RPM operation well, so if you are a spirited driver or spend a lot of time at the track your power steering pump will thank you.
 
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