Michael Galimi
March 1, 2011

Speed is addictive, and we're always striving to go quicker and faster, and it seems to be getting easier in the modern world. Take, for example, the '07 Mustang GT featured on these pages. Last year, we added a Ford Racing Performance Parts supercharger kit, Steeda 10-rib pulley upgrade, custom tuning (Diablo-Sport), and a set of drag radials. That led us down a path of mid-11s with a best of 11.49 at 119 mph (with 479 rwhp through the stock automatic).

This year, the question was: What are we going to do in order to run quicker? Right off the bat, I conjured up a half a dozen ideas to increase power as a means to run quicker down the ol' 1,320. More power equals quicker times, right? In today's world of chassis-dyno racing, that seems to be true. There are, however, other ways to run quicker, and it doesn't involve adding horsepower.

Ultimately, we picked up nearly 0.3 second and we didn't add one horsepower. In fact, all of our testing was done with less horsepower than what was originally thrown down on the dyno-more on that later. Our focus for this story is improving acceleration, and we turned to the drivetrain for some time-honored modifications, namely an aluminum driveshaft, a steeper set of gears, and a looser torque converter. The purpose for the mods was to increase efficiency by utilizing the powerband of our twin-screw-blown, Three-Valve modular engine.

The rear gears are simple-the more gear multiplication, the quicker the car accelerates (to a point). We settled on Ford Racing 4.10 gears as a suitable replacement for the 3.31 factory cogs. Most will scratch their heads and wonder, Why such a steep ratio (numerically higher number) with a twin-screw combo? The goal was to optimize track performance, but not at the cost of the car's street manners.

"A higher numeric gear ratio will allow the engine to accelerate the car more efficiently and keep the car in it's powerband throughout the entire run down the track," said Justin Burcham of JPC Racing. "The optimum scenario for determining your gear ratio is to have your car cross the finish line with the engine just above your shift point. That way, you're using the entire powerband of the engine and crossing the line in the final 1:1 transmission gear at peak rpm."

The lowest gear ratio (though numerically high) we were willing to go with was a 4.10 since we drive the car everywhere. The 4.10s would put our trap speed in the 6,300-rpm range based on the car's previous quarter-mile speed (119 mph) and the Mickey Thompson's 26-inch-tall tire size. The highway rpm range is acceptable as well, as the math shows the engine will run at 2,643 rpm in Overdrive at 70 mph. The 4.10 gear offers the best of both worlds for track and street for this combo. If we add more power, thus increasing trap speed, then we could turn to a taller tire to knock down the finish-line rpm.

The next part on our list of modifications was to dump the heavyweight stock driveshaft for an aluminum one. The factory driveshaft in '05-present Mustangs is a two-piece unit that measures a robust 38 pounds. We picked up an Axle Exchange one-piece aluminum driveshaft that weighs half as much (19 pounds total). That saves 19 pounds from the overall weight, but more importantly its rotating weight. "The lighter driveshaft, like any lightweight drivetrain component, will allow the car to accelerate quicker because the engine doesn't have to waste power to accelerate the extra mass," commented Burcham.

The Axle Exchange one-piece driveshaft for '05-'10 Mustang comes with a price tag of $699. It's made from one-piece Alcoa 6061 T-6 aluminum and has a 4-inch diameter. The one-piece design eliminates the center CV joint, which has been a source of failure as power and traction are increased.

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