Pulley Upper Reduction 15% 3/4in Bore

The Pulley Upper Reduction 15% 3/4in Bore from Coleman Racing Products is a precision-engineered underdrive pulley designed for serious engine builders and performance enthusiasts. This component reduces crankshaft pulley speed by 15 percent, delivering measurable gains in engine efficiency and horsepower by minimizing parasitic losses from accessory-driven systems. Whether you're tuning a street engine or building a high-output track motor, this upper reduction pulley is engineered to lower stress on your charging system and water pump while freeing up valuable power at the flywheel.

The 3/4-inch bore diameter ensures compatibility with standard crankshaft applications and provides a secure, concentrically-balanced interface critical for sustained high-RPM operation. Coleman Racing Products machines this pulley to exacting tolerances, maintaining dynamic balance to prevent harmful vibration that could compromise engine longevity or bearing life. The 15-percent reduction ratio is the ideal sweet spot for naturally aspirated engines—aggressive enough to yield real dyno gains without over-stressing the serpentine belt or creating charging deficiencies under load. Weighing just 1.93 pounds, this component minimizes rotational mass, further improving throttle response and allowing your engine to rev more freely.

Mechanics and engine builders routinely specify underdrive pulleys for both street and competition applications, from small-block Chevys to modern LS platforms. Installation is straightforward on engines with accessible upper pulley access, though proper crankshaft locking and torque verification are essential for reliable assembly. This pulley integrates seamlessly into existing serpentine belt systems and pairs well with high-amp alternators and performance water pumps. Verify your engine's crankshaft bore diameter and pulley mounting configuration before ordering to ensure perfect fitment and maximum performance gains.