For daily driving and casual performance use, modern, electronically controlled automatic transmissions offer an array of advantages over the hydraulic design of older gearboxes. Units like the current six-speed box used in the Mustang have twice as many gears as the transmissions that were installed in Ford’s pony car back in the original muscle car era, and that means that Ford’s engineers can give the box quick ratios in the lower gears to improve off-the-line performance while also yielding great fuel economy with the overdrive cogs used in the higher gears to keep the revs down at highway speeds.

Some of the modern electronically controlled gearboxes in use today also provide levels of customizability in terms of gear change schedules and shift firmness to keep the motor in the power and provide fast response when hustling the vehicle on-track or out on a winding stretch of road. So in general, the modernization of automatic gearboxes is a positive one in nearly all aspects of typical performance. But what if your application goes beyond typical performance?

For those who’re racing competitively and are serious about lowering their e.t.’s, ditching the factory transmission for a purpose-built, hydraulically controlled gearbox that’s configured for racing can make a huge difference in performance. That’s just what we did with this Coyote-powered, 2013 Mustang GT, swapping the factory 6R80 six-speed box for an ATI Performance TH400 three-speed unit that’s dialed in for drag racing. Here we’ll look into the particulars of the transmission swap as well as the other components we added to the mix in order to enhance this pony’s capability at the strip.

Going Turbo Hydra

While some of the differences between the transmission designs are clear from the outset, there’s also some disparities that might not be immediately obvious.

“Obviously you’re losing two overdrives and half the gears,” JC Beattie Jr. of ATI Performance points out. “But some might be surprised to discover that first gear in the stock six-speed isn’t as aggressive as the one used in this TH400. This gearbox will really improve the vehicle’s ability to apply the power at the track, as most modern gearboxes won’t give you full power in First gear – these stock transmissions are designed to be warrantied for 100,000 miles at a specific power level. The TH400 will give the driver full control over the transmission while providing firm shifts and better gear ratio pairing.”

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For OEMs, much the design strategy involves being able to use as many parts across as many vehicles as possible to keep manufacturing costs down and to minimize the chances of broken components in order to avoid warranty claims and a reputation for unreliability. As such, the six-speed gearbox used in the Mustang GT can also be found in luxury vehicles like the Lincoln Navigator as well as F-Series trucks. Each of these vehicles have decidedly different core missions, and for drag racers who want a gearbox that's tailored specifically for racing, swapping over to an ATI gearbox like this one — which can be configured with 12 different First gear ratios based on power output, tires, weight, and other racing factors — puts full control of the transmission's operation in their hands, and that includes the use of all the engine’s power right off the line.

While we tend to think of modern gearboxes as being more efficient due to all the technology in them, JC points out that in certain instances, the result is actually quite the opposite.

“Since there’s less going on in the TH400 there’s less hardware for the power to go through, and in turn, there’s less opportunity for parasitic loss,” he explained.“You’re also getting rid of quite a bit of weight in the process, and OEM torque converters are not aggressive with the pump angle and stator. The OEM torque converter’s job isn’t so much to multiply torque as it is to transfer power continuously and smoothly.”

With performance being the top priority in ATI’s transmission design, the compromises made by OEMs in order to keep the car’s street manners within the company’s guidelines for noise, harshness and vibration don’t really apply here.

“We’ve had a couple race converters returned to us because those customers thought they were too violent,” he adds. “A good torque converter can be the difference between 4-foot wheelies and lifting the tires an inch off the ground.”

When adapting a Brand X-style gearbox to work in the Mustang, builders have two main options for installation strategy.

“You can cut the stock bellhousing and, using a locating ring, hook the Ford mod motor to it,” JC said. “Our kit comes with the flexplate, adapter and all the hardware to make it a drop-in installation.”

For those who would prefer not to modify the stock bellhousing, ATI Performance also offers an aftermarket case that bolts right in with no locating ring needed.

“It’s a nice and easy setup,” he tells us. “The transmission is going to bolt up like the one that came out of the car, but you’ll still want to check for clearance. The crossmember has to be changed, and since the two transmissions are different lengths (the 6R80 is longer than the TH400), the driveshaft will need to be swapped as well. The shifter and the dip stick will need to be changed over too, of course.”

ATI also offers builders a number of configuration options when they’re ordering a transmission, including 12 different First-gear options depending on the vehicle’s weight, the tire being used, the type application it’s being used in, and how much power the gearbox needs to contend with. ATI builds boxes that can to handle up to 4,500 horsepower.

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The longer dimensions of the 6R80 transmission coming out of the car (shown top left) means that the stock driveshaft won't be long enough to work with the shorter TH400 that’s replacing it. But aside the driveshaft, shifter and potentially the crossmember needing to be swapped for pieces that are compatible with the ATI gearbox, this transmission swap is a pretty straightforward operation. You need to use a locating ring in order to hook the new gearbox to the Coyote motor if you choose to cut the stock bellhousing, but ATI also offers aftermarket bellhousing that bolts right up with no locating ring needed.

“We have a street/strip line, then a mild race line which is 800-1,500 horsepower,” he said. “After 1,500 (and up to 2,500 horsepower), every single piece is changed versus the lower-horsepower units, as well as the materials and manufacturing process. After 2,500, we’re talking about Pro Nitrous-level performance – larger input shafts, aluminum pumps, etc, to handle the five stages of nitrous being used.”

Fluid Dynamics

Many folks tend to overlook the importance of choosing the right fluid for a particular application, assuming that there’s little difference between two performance transmission fluids, if any. But after speaking with the folks at Driven Racing Oil, who helped develop the transmission fluid that ATI uses in its TH400 gearboxes, it’s clear that this conventional wisdom is flawed at best.

“The fluid you choose for an application like this definitely matters,” Lake Speed Jr., of Driven Racing Oil, said. “We worked with ATI to develop this fluid to address the specific stresses of the performance applications these transmissions are used in. Many modern fluids are optimized to provide smoother shifts, and what ATI has been seeing is that these fluids tend to cause more slippage, which leads to overheating the bands and premature wear.”

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Lake Speed of Driven Racing Oil says that a lot of folks that he talks to say that they choose their fluids based on brand trust, which is rooted in sound logic but not an ideal approach if you're looking to maximize the performance and longevity of the hardware the fluid is going to be used with. "There is no one-size-fits-all transmission fluid," he explains. "Although they're both automatics, a modern eight-speed transmission is a completely different animal than something like a TH400."

“We spent a lot of time with JC and the engineers at ATI in the testing and development process,” Lake added. “It was truly a combined effort – we started with a formula based on the attributes they wanted in their transmissions. The frictional characteristics need to be right – you don’t want excessive drag between components, but you also want it to hold before the clutch is engaged. We also needed to have the correct fluid properties – it needs to release air properly so it isn’t holding air in. It shouldn’t be compressible.”

Lake also explained that along with real-world testing out at the track, a transmission dyno helps engineers fine tune for the formula.

“Telemetry data can tell us a lot, especially in road racing and endurance applications,” he said. “But with the dyno we can monitor very specific changes – does this formula make the transmission run hotter? Colder? When we zero in on a formula that looks good, we can then head to the track for testing, see how it performs, and then return to the dyno and run those tests again to get the full story.”

Lake said that for applications under 1,500 horsepower, Driven recommends its 20-weight Super F fluid, while applications above 1,500 horsepower should go with the company’s 30-weight Max Duty fluid.

Due to its lighter weight, the Super F fluid provides several key advantages for a racing transmission in applications under 1,500 horsepower, since its lighter weight allows it to move through the transmission with greater ease while also increasing torque converter flash by roughly 100 rpm and decreasing transmission pressure by about 10 pounds, thereby improving the transmission’s overall performance and helping to lower those e.t.’s.

The Right Shifter

As mentioned earlier, the transmission swap also requires changing out the shifter as well, so we selected the TCI Automotive Outlaw shifter for the job due to its solid feature set and sharp looks.

“The Outlaw shifter features a removable gate plate that has positive stops for each gear,” Kevin Winstead, of TCI, said.

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The stock shifter isn’t compatible with the TH400, so we swapped it out with this NHRA-compliant TCI Outlaw shifter. It features billet aluminum construction, a reverse lockout that prevents accidental shifts into reverse, and a park/neutral safety switch.

Featuring billet aluminum construction, a pistol-grip shifter and a black-anodized cover with an optional quick release setup, this shifter is designed to be easy to live with on the street but durable enough for racing applications as well.

“While being light weight, the billet aluminum construction makes this shifter strong enough to handle the rigors of regular track use,” Kevin reiterated.

The shifter is available with either two-, three- or four-speed gate plates and can be purchased with or without a cover. Other options include a single push button switch or dual switches as well as an electric shift option. Further bolstering its race readiness is the shifter’s full NHRA compliance.

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With the stock gearbox already being removed, most of the work involved with removing the stock shifter was already taken care of. Bolting up the new shifter was simply a matter of hooking it up to the new transmission once that was connected to the rest of the drivetrain and buttoning everything up by reinstalling the various pieces of the center console.

“The NHRA requires that a vehicle’s shifter must have a reverse lockout mechanism in order to be compliant,” Kevin explained. “The lockout ensures that the shifter can’t be accidentally shifted into reverse at speed.”

Controlling the Launch

While we were in the process of the transmission swap we added a pair of components from MSD Performance that should help cut our e.t.’s down even further.

The MSD Two-Step Launch Controller (PN 8731) connects right up to late-model Fords to aid in consistent launching and better 60-foot times by allowing the operator to set an RPM limit to stage with. Similar to the OEM launch control systems found on some late model performance cars, when the two-step launch controller is activated it will hold the engine RPM at that pre-determined level and once the green light comes on, you’re ready for takeoff.

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MSD's kit includes the module itself as well as a wiring harness and the requisite hardware. RPM adjustments are made on the rotary dials seen on the side of the module in the image on the left.

Once installed, setting up the controller is a hassle-free process. Adjusting the launch RPM to taste is dead simple using the two built-in rotary dials, which allow you to make adjustments in 100 RPM increments ranging from 1,800-9,900 RPM.

The other piece of the MSD equation here is their digital shift light (PN 89631). As you might expect, this shift light alerts the driver when they should upshift to the next gear, reducing any chance of over-revving while in the midst of barreling down the drag strip at wide-open throttle. Six red LED lights are triggered when the engine RPM reach the programmed point in the rev range, and the light allows for up to four different values for use with different gears, if needed.

All in, these modifications should comprehensively transform this Coyote-powered Mustang’s capability at the track while keeping the car reasonably streetable when needed.

Looking to replace your pony’s transmission with something that’s purpose-built for drag strip capability? Give the folks at ATI Performance a buzz and see what’s available for your project, and don’t forget to check out the offerings from Driven Racing Oil, MSD Performance, and TCI Automotive when you’re ready to start shopping for the ancillary components that will help bring this swap together and maximize its benefits out at the track.