Power managed foolishly pretty much leaves you sitting there with your pride (or broken parts) in your hand. Managing the power for your project doesn't just mean building a tough-as-nails engine that will crack the 400-horse mark on a dyno. No, you have to consider that the 400 rampaging horses coming off your engine's flywheel have to be channeled through a transmission, driveshaft, and, ultimately, to the rearend where the power is transferred to the pavement.
When we consider getting that power to the pavement, we think about tires, traction bars, shocks, springs, torque arms, and more. But do we ever consider the differential? We don't give that chunk of steel enough of our time, especially during the planning phase of our projects. The transmission gets pulled for a complete overhaul, the driveshaft gets new U-joints and balancing, but what happens to the rear? The rearend usually only gets our full attention when it breaks, or when we get spanked that first Saturday night at the drag strip because we didn't calculate the proper gear for the power on board. We wind up picking up the rearend pieces because we forget to build for 450 hp.
Our point? You can't get there effectively with a smelly, old, worn-out differential. You have to plan your differential just like you plan the engine, transmission, chassis, and brakes. This means setting aside some of your project building budget, thinking about your overall desires and needs, and picking the proper parts to build a sound and reliable rear that can handle what you've got in mind. Remember, building a rear for your project is different than adding a stereo system or a billet grille--you really don't want to go back and upgrade later.
Spend the money now and build the rear your project will need for now, as well as into the future.
Planning For Power
Your differential build plan needs to begin just like the rest of the car's building and driving plan.
- How do you intend to use the vehicle?
- How much power do you intend for your engine to make?
- Will your transmission have overdrive?
- What's your budget?
- How do you choose a differential, rear axle housing, and all of the components?
Currie Enterprises offers the most extensive line of differentials and rear axles in the world and has been upgrading Ford rears for decades. We're going to focus on what's most popular with Ford buffs: the removable carrier 8- and 9-inch rear axle assemblies available in Fords since 1957.
This is Currie's basic 9-inch carrier based on the C7AW-E Ford casting. Currie throws a little more meat into the places where it counts, such as around the pinion pilot. That makes this stronger than the factory C7AW-E casting. For less money, Currie will sell you the stock C7AW-E gray iron casting for under $100.
Used Currie C7AW-E Casting Price: $79.95
New Currie C7AW-E Casting Price: N/A
Here's the Currie 9-Plus Sportsman...
Here's the Currie 9-Plus Sportsman casting assembled. This is a nice, durable case complete with caps, bolts, billet spanner nuts, and spanner nut retainers. This one takes up to 600 hp.
Currie 9-Plus Sportsman Casting Price: $257.07
Currie's 9-Plus Race Case...
Currie's 9-Plus Race Case casting is cast from 65,000-psi nodular iron. There are two versions sporting different carrier bearing bore sizes (3.062 and 3.250 inches) designed to accommodate 28- and 31-spline, and 35- and 40-spline hubs and axles...
...This guy will take up to...
...This guy will take up to 850 hp.
Currie 9-Plus Race Casting Price: $384.20
PN 4027 (3.062" Carrier Bearing)
PN 4028 (3.250" Carrier Bearing)