Muscle Mustangs & Fast FordsHow To Drivetrain
2007 Ford Mustang Drivetrain Upgrades - Accelerate Your Life
Improving The Drivetrain Efficiency Is As Good As Adding More Horsepower And Torque.
To keep it all honest, we kept the street tune in the PCM for the after-testing with the TCI torque converter and Axle Exchange driveshaft. We ventured to Atco Raceway to get some on-track results. The gains were instantly realized as our GT ran 11.31 at 120.04 mph. That was a 0.27-second improvement over our previous best of 11.58 with reduced timing. The mph was similar, but the time was quicker thanks to a better 60-foot. The 11.58 came by way of a 1.71, and the 11.31 featured a 1.57 short time.
The 11.31 wasn't enough, so we plugged in the DiabloSport Trinity hand-held tuner and added a degree of timing through the entire curve, bringing it to 17 degrees at 6,500 rpm. Our car dug in, rocketed through the 60-foot clocks with the same 1.57, and made it to the finish line with a new best of 11.24 at 120.62 mph. Not bad for a car we drove to the track, swapped the tires, and only cooled down by opening the hood. On the street, the car is an animal, and the only difference is that the torque converter feels slightly looser.
Now we're thinking-with low 11s so easy, what would it take to run 10s?
MPH x Rear Gear x 336 (constant) / Tire Height
119 x 4.10 x 336 / 26.0 = 6,305 rpm
On track and at 119 mph, the rpm will be screaming at 6,305 since we run on 26-inch-tall ET Street DOT tires. Given tire growth, the rpm will probably be a little lower, but we don't have an accurate way of accounting for it. Radials won't grow like bias-ply meats, so that factors into finish-line rpm as well. According to Burcham, ideally you want to select a gear ratio that will rev the engine no more than 500 rpm past your peak horsepower. If the finish-line rpm is above 500 rpm, then a numerically lower rear gear is needed or a switch to taller tires, which effectively changes the gear ratio. Burcham also suggested that if you are crossing the stripe and the engine is below peak hp rpm, then its time to add a more rear gear.
To calculate highway cruising speeds in Overdrive, simply take the trans Overdrive ratio and multiply it by the formula's result. In our case, a 70-mph cruising speed combined with the street-tire height of 25.9 inches gives us an engine speed of 3,723 rpm. The 5R55S has a 0.71:1 Overdrive gear, so it would knock the cruising rpm down to 2,643 rpm (3,723 x 0.71).