Under Drive Pulley

What is an Under Drive Pulley (UDP)?

A UDP is a pulley that is smaller in size than the stock pulley that came on your car. It is an after-market part that you can purchase from several venders.

What does the UDP do?

The purpose of a UDP is to slow down the accesory pullies so that the engine doesn't have to work as hard to spin everything. This in turn allows more of the horsepower generated by the engine to be sent to the rear wheels. This is not to be confused with "making" more HP, just freeing up the HP that is already there.