Wayne Cook
September 8, 2010

Tech | Drivetrain Upgrade
Our '68 Torino GT is factory original in every way except for a 4V carb and intake. At just over 100,000 miles, the drivetrain seems to be fine, making no serious noises. We're planning on some power upgrades in months to come and when the opportunity arose to visit Currie Enterprises of Anaheim, California, to have the company inspect the rear axle on our car, we we're glad to visit.

Currie is a time-tested leader in rear axle technology, and it is the only outfit we know of that covers such a wide scope of third member possibilities. Currie won't try to sell you an axle that will support 1,000 horsepower for your weekend-driven 289 Mustang, but rather recommend just the sort of upgrade that's appropriate to your application. In our case, we wanted to upgrade our existing unit to handle perhaps an expected maximum of 250 horsepower at the tire. Currie can build an 8-inch axle for any project, but it is reluctant to do so for projects where more than 300 rear wheel horsepower is anticipated.

When a Mustang was equipped with a K-code engine making 271 horsepower, the car got a 9-inch axle. We wanted to see what Currie would recommend and what procedures that it would perform to turn our 8-inch differential into a bolstered brute, and we learned that the real secret to building a durable axle is careful component inspection and assembly procedure.

Although we don't plan on using our car for drag racing, we wanted the strongest possible assembly using our stock components and a Currie TSD or "torque sensing differential." This differential would replace the open factory unit and provide traction to both wheels simultaneously, while being quiet in the turns. In our past experience we've had great success with the Currie TSD and we were jazzed to have one installed into the peg-leg Torino.

There are different kinds of performance and for this car we want open road prowess. The car doesn't have an overdrive transmission (yet) but with the car's 2.79 gears and relatively tall tires, the car goes 75 miles per hour at 2,400 rpm. We'd like to have the added acceleration that a 3.50 gear would provide, but with a 1:1 final drive ratio at the transmission, the long legs would be gone. Nothing takes the fun out of a road trip for us like having big rigs blow by you like you're tied to a tree. For this reason we elected to stay with the stock gears and will consider changing to a deeper ratio if the car ever receives an overdrive transmission.

For higher performance applications using an 8-inch axle, Currie now offers an aluminum gearcase casting capable of supporting more horsepower. Once we get into the category of 9-inch axles, the range of selection at Currie is almost endless. With its line of excellent 9+ products, as well as modern 8.8-inch axle possibilities, Currie Enterprises can construct an axle that's perfectly suited to your application and your budget.

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