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The underdrive pulley operates under a very simple principle. If the crank pulley is smaller than normal, it has more mechanical leverage to spin up. Sort of like 1st gear versus 2nd gear. In theory this presents a performance benefit (the energy saved is now instead used to put the wheels to the ground harder).

BEFORE:
The stock crankcase pulley weighs about 5+ pounds and is about 6 inches in diameter.



AFTER:
The Unorthodox underdrive pulley is about 2+ pounds in weight and about 4.5 inches in diameter.



Here's the UDP installed with the stock pulley underneath as a comparison. I didn't realize this before, I have this whole "red' color thing going on underneath the engine bay, with red plug wires, red silicon connector, and red UDP.

Removing the old pulley setup wasn't too difficult. The worst part was grinding the metal around the slot that the stock pulley fits around. And of course, it was very difficult untorquing the bolt that holds the pulley in place. Everything else was cake compared to these two things.



Cost Analysis

I Spent:
$199, 179 for the pulley plus 20 dollars 2nd day shipping.

When:
June 1998