Underdrive pulleys can raise fuel mileage by decreasing load on an engine. An underdrive pulley is a pulley that has a smaller diameter than a car’s stock pulley. These pulleys reduce load on a motor. Specifically, they decrease resistance on the accessory drive belt which is connected to the crankshaft via the crank pulley. By reducing load on the crankshaft the pistons are free to move up and down with less resistance. This means it takes lesser amount of fuel to travel the same distance because you have freed up power in the motor. Usually underdrive pulleys are sold in kits of 2 or 3 pulleys including a new crankshaft pulley and alternator pulley.
1. Pulley Kits
Buy an underdrive pulley kit for your specific make and model year vehicle. There are many companies out there that sell pulleys made specifically for your car. A few that come to mind are March Performance Pulleys, Moroso, Trick Flow, ASP Pulleys, and BBK Performance.
2. Gas Mileage Gains
Some companies claim up to a 4% increase in fuel mileage by installing their underdrive pulleys. Make sure when buying underdrive pulleys you also purchase the recommended drive belt to fit your new pulley setup as your original drive belt will now be too large to fit.
Here at MPG Enhance we have tested an underdrive pulley setup installed on a late 90’s Pontiac Firebird LT1 motor. The response was phenomenal! Vehicle acceleration was markedly increased and roughly ten horsepower was gained. The vehicle climbed the rpm band much quicker and with less application of fuel. In addition gas mileage gains were approximately 1 mpg. This modification is highly recommended.