What's an underdrive pulley?

An underdrive pulley is a replacement pulley that bolts up the same as stock, but has a different size (ratio) and material specifications intended to free up lost horsepower. By increasing the diameter of each accessory pulley and decreasing the size of the crank pulley, the speed at which the accessories are turning relative to engine RPM decreases.

Under drive pulleys do not add power to the engine, they free up the power that is normally wasted on overdriven accessories. The theory is that a larger pulley will drive the accessories slower thus reducing their parasitic horsepower loss. No more power total, but more power sent to the wheels. As an additional benefit, the reduction in wear (less usage) on the accessories due to the lower duty cycles can extend the life of these parts.

For example, the alternator, power steering, water pump and air compressor rob horsepower from the engine. By replacing factory-sized crank balancer/pulley and water pump drive pulley with a resized pulleys, the accessories are slowed, resulting in more horsepower available to the drive wheels.

MOTOBLUE™ H.O. Series pulleys will increase horsepower up to 12 RWHP, and increase mileage by 1 to 2 MPG. MOTOBLUE H.O Pulleys are manufactured from billet steel, exceeding factory quality and are the only Pulley system available on the market today that are SFI approved for all racing applications.

Installation: The kit includes all required components and hardware for a complete installation.

Tech Notes: Use of Harmonic Balancer Puller tool required for factory Harmonic Balancer removal.

MOTOBLUE™ SFI Approved H.O. Series Power Pulley Kit
• 04 & Up Ford F-150 Truck, Navigator, Expedition, Ford Trucks as equipped
• H.O. 25% Harmonic SFI Approved Balancer
• H.O. 26% Water Pump Pulley
• Complete kit with installation bolt and new replacement balancer bolt

A PowerStat low-temp thermostat improves performance in two ways: first by increasing the mass flow rate of intake air, and second by reducing the engine's tendency to detonate.

From the laws of physics, cooler air is denser than warmer air. Since horsepower increases as the amount of air and fuel burned increases, cooler air (with more air molecules per cubic inch) makes more power. The PowerStat allows the engine to cool down to a lower temperature than the factory thermostat to make more power. At the drag races, water can be sprayed on the radiator between races to drop the temperature and improve performance. The PowerStat ensures that you leave the line at the same temperature on each run to give consistent maximum performance for bracket racing.

Detonation, usually producing audible pinging or even knocking sounds, refers to the spontaneous explosion of the unburned air/fuel mixture in the combustion chamber. Detonation abruptly and violently ends the normal combustion process, reduces power, and can severely damage the engine. A PowerStat reduces the temperature of both the incoming air/fuel mixture and the surfaces of the combustion chamber, greatly reducing the tendency to detonate. This allows the engine to safely develop more horsepower. PowerStats should always be used in an engine controlled by a computer to insure consistent performance.

Increases Mass Flow Rate of Intake Air Allows Engine to Cool Down to Lower Temperature than Factory Thermostats Reduces Engine's Tendency to Detonate Reduces Temperature of Both the Incoming Air/Fuel Mixture and Combustion Chamber Surface

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