Ford 9 Inch Rear End Upgrade - Horsepower Hookup

Gearing For Power
An engine that produces neck-snapping torque and horsepower without the correct gearing might as well be a boat anchor. Internal combustion engines require rpm multiplication through a transmission and differential gears. The transmission controls the engine's rpm range by making gear changes that transfer the engine's torque and power peaks to the differential. The driveshaft links the torque and power from the engine's transmission and sends it to the differential. The driveshaft is connected to the pinion gear and intersects with the ring gear to drive the axles. This moves the vehicle forward or backward.

When increasing the wheel/tire size it is always a good idea to check the engine's torque and power zones at highway speed. You don't want to make an increased tire size change and find out you have lost 500 rpm during highway cruising mode. Keeping your tachometer reading around 2,000-2,500 rpm will maintain your engine performance and fuel mileage. Increasing the rear tire diameter means the tire rollout was increased and this will affect your fuel mileage. To adjust the engine rpm and wheel/tire rpm, a ring-and-pinion gear change is the answer.

We spent some time at Currie Enterprises in Anaheim, CA, with project managaer Brian Shepard, and Armando Nila, their technician "Ace", as he refurbished a Ford 9-inch rearend with a new ring-and-pinion gear set, pinion support bearings, axle races, shims, seals and bearings, third member gasket, and T.S.D (torque sensing differential) limited slip unit.