UDP stands for under drive pulley, available as a 50% or a 25% under drive pulley, from escortfocus.com. These turn the engine driven accessories slower to allow more of the engine's power to be used at the drive wheels. The 50% UDP can reduce quarter mile accelerations times up to 3/10 second and make a substantial increase in your fuel economy. It's especially useful while using the air conditioning. You no longer will feel the car slow down every time the a/c compressor cycles. There are no real dowsides to using a UDP. They will pay for themselves in fuel savings alone. They have no effect on engine cooling since the water pump is run from the camshaft timing belt. In most cases, the 50% is the best way to go since the power and fuel economy savings will be maximized. If a lot of driving is done in stop and go traffic or there is a heavy load on the electrical system, then maybe the 24% pulley is better. The 50% does not allow the alternator to charge properly at an idle, and will typically begin charging after 1000 rpms. The battery power will suffice in these cases for a few occasional minutes, and once the car begins to drive again the alternator will charge normally and restore the power.

Installation is rather easy and can be done either with a breaker bar or an impact gun.

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