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™ H.O. Series Power Pulley Kit
• H.O. 25% SFI Approved Replacement Harmonic Balancer Pulley
• H.O. Water Pump Pulley
• H.O. GEN II Idler Pulley
• Retains Stock belt

RPM is proud to announce the introduction of the NEW MOTOBLUE™ GEN X and the Original GEN II BILLET IDLER Pulleys.

Replace your factory hi drag, low quality stamped steel OEM idler pulleys with either the new MOTOBLUE™ GEN X double bearing cnc machined pulley or the original GEN II single bearing cnc machined billet idler pullies.

MOTOBLUE™ GEN X and original GEN II are CNC machined from aircraft quality 6160 billet aluminum. CNC machined for a perfect fit featuring the highest quality “sealed for life” bearings.

The NEW GEN X 90 MM double bearing has been designed specifically to eliminate high RPM wobble common to auxiliary idler pulleys on supercharged applications . The NEW Gen X effectively eliminates any bearing failure caused by supercharger belt side load. This is the same technology that industrial supercharger manufactures use for high load supercharged belt driven systems.

Installation does not require any modification, Hardware and detailed instructions included for a trouble free installation. Choose your own combination of 90mm and 100mm Pulleys. These pulleys are in stock and available for same day shipping.

MOTOBLUE™ GEN X Pulley
• 90mm Double Bearing Billet Idler Pulley Kit
• SILVER Hard Anodized Finish Machined Face
• CNC 6160 billet aluminum, “sealed for life” bearings

MOTOBLUE™ GEN X Pulley
• 90mm Double Bearing Billet Idler Pulley Kit
• BLACK Hard Anodized Finish Machined Face
• CNC 6160 billet aluminum, “sealed for life” bearings

MOTOBLUE™ GEN II Pulley
• 90mm Billet Idler Replacement Pulley
• SILVER Hard Anodized Finish Machined Face
• CNC 6160 billet aluminum, “sealed for life” bearing

MOTOBLUE™ GEN II Pulley
• 90mm Billet Idler Replacement Pulley
• BLACK Hard Anodized Finish Machined Face
• CNC 6160 billet aluminum, “sealed for life” bearing

MOTOBLUE™ GEN II Pulley
• 100mm Billet Idler Replacement Pulley
• SILVER Hard Anodized Finish Machined Face
• CNC 6160 billet aluminum, “sealed for life” bearing

MOTOBLUE™ GEN II Pulley
• 100mm Billet Idler Replacement Pulley
• BLACK Hard Anodized Finish Machined Face
• CNC 6160 billet aluminum, “sealed for life” bearing

Replace your factory hi drag, low quality stamped steel OEM idler pulleys with the MOTOBLUE™ GEN X double bearing cnc machined billet aluminum idler pulley.

The MOTOBLUE™ GEN X 90 MM double bearing has been designed specifically to eliminate high RPM wobble common to auxiliary idler pulleys on supercharged applications.

The MOTOBLUE™ GEN X 90 MM double bearing effectively eliminates any bearing failure caused by supercharger belt side load. This is the same technology that industrial supercharger manufactures use for high load supercharged belt driven systems.

Installation does not require any modification, Hardware and detailed instructions included for a trouble free installation. These pulleys are in stock and available for same day shipping.

MOTOBLUE™ GEN X Pulley
• 90mm Double Bearing Billet Idler Pulley Kit
• SILVER Hard Anodized Finish Machined Face
• CNC 6160 billet aluminum, “sealed for life” bearings

MOTOBLUE™ GEN X Pulley
• 90mm Double Bearing Billet Idler Pulley Kit
• BLACK Hard Anodized Finish Machined Face
• CNC 6160 billet aluminum, “sealed for life” bearings