Since building gratuitous amounts of horsepower is getting easier and easier every day, it's not a far-out thought to have a street car putting out 700 to 1,000hp. With that level of power on tap, all the stuff behind the engine gets put though the proverbial wringer. We are going to run into that exact situation with a car our editor is building.
When asked about his new ride, he responded, "The car is a '72 Nova SS that I bought sans motor. It was set up for a 454, but I'll be putting in a 509ci Dart big-block and a lightweight TCI front clip. It was mini-tubbed before I bought it, but the previous owner kept the 10-bolt in it, which won't last five minutes behind the 669hp Rat, hence the need for a stronger rearend. It should be a fun street/strip car that'll (I hope) run high 10s on street tires, then maybe 9s when we hit it with some nitrous."
As you can tell from his plan, the car will be flogged on a regular basis and will see the business end of a nitrous bottle at some point. To keep all the power under control and transfer it to the tarmac, the vehicle will need a rear that can take the abuse of a lead-footed editor. Enter Currie Enterprises and the company's F9 fabricated 9-inch. This built-to-order differential can be built in multiple power-handling capacities to suit your specific needs and budget.
On Currie's recommendation, we decided on an F9 with 3-inch axle tubes, 35-spline axles, nodular iron 9+ Race Gear Case, 9+ Big Bearing pinion support, 9+ nodular iron yoke for a 1350 U-joint, and large bearing housing ends (Torino-style). Everything we just listed is actually made by Currie in house, well except for the casting/forging process. They make it all right down to the wheel studs and other hardware.
The only outside parts we needed to order were the Motive Gear 3.70:1 gear set and the Detroit TrueTrac helical gear differential. The gears will work great with the 27.8-inch diameter back tires and the TrueTrac will distribute the power to both wheels while still being streetable.
Currie recommended the TrueTrac for our F9 application. The TrueTrac differential from Eaton distributes power to both wheels without using wearable parts like clutch plates and springs found in traditional limited-slip differentials. The TruTrac uses a set of helical gears that mesh with side gears to allow one wheel to spin under light load for better street drivability. Once some torque is applied the gears lock up inside the diff and send power down both axles.
Currie uses Motive Gears in all the rearends it builds. "We use Motive Gears because we found they are high quality and provide quiet operation. Plus, Motive offers a tremendous range of ratios so we feel confident in getting the customer exactly what they want," said Brian Shephard from Currie.
Currie can install traditional street/strip gears like in our rearend or they can put in a soft, lightweight AX Motive Gear for full competition use.
We invaded the Currie building and followed the process of how the company builds this rear from basically scratch. Once the rearend was completed, it would be able to handle 1,000-1,200hp and live a nice long life under the Nova. Now if our editor Jim gets a little power hungry and upgrades the engine past 1,200hp, we'll need to have an even stouter rearend built by Currie, maybe a chrome-moly housing with 4-inch tubes and 40-spline axles.
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Here is the center of the F9 rearend that Currie designed and built. The housing body is b
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Here is a look at the gussets used to strengthen the third member face.
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Like we stated in the opening text, Currie builds the F9 from scratch, so the axle tubes s
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Then the tubes are chucked in a lathe where they are cut to the perfect size. The inner di
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One key feature to adding durability to the complete unit is how Currie indexes the axle t
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Here you can see where the flat part that was just cut in the tube indexes into the F9 hou