Steve Baur
Former Editor, Modified Mustangs & Fords
January 1, 2008
This '04 Cobra, No. 3,620, has logged only 12,800 miles, many of them a quarter-mile at the time.

If you've been reading Muscle Mustangs & Fast Fords for some time, you've no doubt seen all of the press that the supercharged '03-'04 SVT Cobras have received. Many people knew beforehand that modular engines liked forced induction, but things really took off once Ford equipped its top-tier Mustang with a bulletproof short-block and a supercharger.

Starting out with 390 hp from the factory, induction and exhaust bolt-ons made 450-500 rwhp seem like child's play. Soon, there were 550-, 600-, 700-rwhp cars out there on the street.

Transmission-wise, the Terminator ('03-'04) Cobras' T56 gearbox is a stout piece and handles most of what Cobra owners throw at them. Clutches, on the other hand, don't last as long, and most Cobra owners know they have to sacrifice clutch longevity for quick elapsed times. The weight of the supercharged Cobras is also an issue.

The good thing is, the aftermarket has you covered on clutch and T56 upgrades, but what if your car is too fast for your driving-skill level? Or maybe you just don't want to drive a stick anymore? There's an answer, and it comes in the form of a 4R75W swap.

BC Automotive shipped the 4R75W transmission, torque converter, and transmission cooler all in one package.

Craig Smith of Jacksonville, Florida, is a retired electrician who regularly enjoys driving the wheels off of his '04 Cobra. His venomous snake is a little more potent these days thanks to the Kenne Bell supercharger and a 100-shot of nitrous oxide, in addition to a full complement of bolt-ons. At 62 years of age and troubled by an occasional bad back, Smith found it increasingly difficult to properly powershift the T56 like it needs to be and sought a remedy for the situation.

In the Jan. '07 issue of MM&FF, we followed along as Orange Park, Florida's HP Performance installed a 4R70W in a Bullitt Mustang. Since that time, HP did another auto swap in a bone-stock Terminator. While we didn't get to cover that one, we grabbed our cameras when we learned the company had another one lined up, this time on Smith's Cobra. What made this deal even better was that Smith had baseline track numbers and was more than willing to blast down the 1,320 for some post-swap testing.

The T56-to-4R75W swap is much like the one we performed on the Bullitt Mustang. Having a great experience with the company before, HP went back to BC Automotive, which built the Bullitt's 4R75W, and ordered a 4R75W automatic transmission and lock-up torque converter.

BC modifies the trans with upgraded bands, a stainless steel forward sun shell, and gears. They also fit extra clutches into the internals to spread the torque load across more area.

"We tightened up the torque converter for this application because of the power characteristics of the engine," said BC's Darrin Burch. The extra low-end grunt of the twin-screw supercharger and nitrous combination will work the converter a little harder, and after modification, an approxi-mate stall speed of 3,200 rpm was achieved. The torque converter is a lock-up unit that features furnace-brazed fins, a billet lockup piston, Torrington bearings, and a large-diameter clutch for added surface area.

The total power handling capability for this transmission is tested continually throughout BC Automotive's customer base. Burch says he has had a 4R75W behind a 700-rwhp twin-turbo car with no problems, and that he wouldn't be surprised to see it handle up to 800. "At that point, something will probably break, and we'll just fix that until the next weak link appears," he says. At that kind of power level, most people go for a C4, but if you like your Overdrive, BC Automotive has you covered.

That being said, you may want to think about where your supercharged Cobra is headed in terms of modifications and final power output. The BC trans and converter package retails for about $3,400 by itself. HP Performance's Tony Gonyon noted that having it installed, along with the additional parts involved, can bring the total price near $5,000.

Our subject vehicle had been upgraded with an aftermarket clutch, flywheel, and numerous transmission mods, which probably add up to a G-note or two, which is about what you can sell the setup for used. Two-Valve owners wanting to upgrade are usually on the lookout for this type of deal, so keep that in mind.

Now that we've decided to automate this Mustang, here are a few things regarding the installation that you may want to make note of.

Our subject vehicle had been equipped with BBK long-tube headers. The passenger-side ball and socket flange was extremely close to the transmission pan, so the pan was slightly modified for clearance. We've also heard that the Kooks headers for the Cobra will fit the automatic too.

One of the key components in this install is the transmission harness, which is procured from any '96-up automatic Mustang GT. Unlike the GT and Mach 1s, the Cobra has no provision in the main harness to plug in the transmission harness, so the end must be repinned into the ECM. The transmission harness is made up of 12 wires that go through a grommet in the tunnel and directly to the PCM. Wire count may vary depending on what wires you reuse.

The '03-'04 Cobras use two intake air-temperature sensors. A primary sensor is located near the MAF, and the downstream sensor is located in the intake manifold. The Mach 1 computer that is used does not have the two-sensor application built into the processor, so the primary is disconnected and the downstream is wired into the primary pin.

Speaking of processors, the Mach 1 SYM2 processor is the computer of choice, as it's the fastest ECM before Ford changed to the '05-and-newer Spanish Oak processors.

The intercooler pump relay is controlled by the Cobra ECM through a ground circuit. Since the Mach processor has no provision for this, the intercooler relay is wired to a chassis ground and comes on at the turn of the ignition key. This isn't a big deal since many Cobra owners put the intercooler pump relay on a switch anyway.

Where there would normally be an Overdrive light on the dash in a factory-automatic Mustang, the Cobra has a shift light for the manual trans. HP simply removes the bulb in the dash; otherwise, it stays on all of the time.

While you're under the dash, you'll want to connect the Neutral safety switch on the clutch pedal to the transmission selector module on the auto transmission. This will ensure that the car starts in only Neutral or Park.

The transmission tunnels are also different between automatic and manual-equipped Mustangs. There is a plate welded to the top of the tunnel on the manual cars, and if you install the auto shifter inside the car, it will sit too high for the factory bezel to snap back in place. You can cut and reposition the plate, but HP remedies this in a much easier fashion by utilizing spacers and mounting the shifter from underneath the vehicle.

Lastly, a 111/42-inch longer driveshaft is required and needs to have a 4R75W yoke. You can reuse the Cobra flange at the other end. It does require a stepped U-joint to mate them, but you can get it from the local parts house, or any good drive-shaft shop should have it in stock and can install it when they make the driveshaft.

With all of the particulars out the of the way, we can tell you that car owner Smith had an ear-to-ear grin after his first test drive behind the automatic.

On the dyno, the peak numbers suffered, but we expected a slight decrease due to increased frictional losses. Baseline horsepower was 643 (735 on nitrous) and 572 lb-ft of torque (713 on squeeze). After the automatic installation, horsepower checked in at 584 and 630 on the sauce. Torque registered 527 lb-ft naturally aspirated and 612 on nitrous.

The driveshaft needs to be 111/42 inches longer. The yoke also needs to be changed to a 4R75W piece. You can reuse the Cobra flange at the other end. It does require a stepped U-joint to mate them.

At the track, this '04 Cobra had run a best elapsed time of 10.74 at 131 mph. Smith, who for more than a year hadn't made any passes in the car, jumped in and ran 11.08, riding the brake pedal. "I accidentally left my foot on the brake pedal because I was getting ready to shift the next gear," he says.

We met up with Smith the following week at the first Mustang vs. GTO Shootout in Gainesville, Florida, and our boy made an easy pass in 10.85 seconds at 128 mph. Traction is now an issue as the automatic has transformed the nitrous-oxide's effect on the torque curve. With HP's Tony Gonyon at the wheel, the snake charged to another traction-limited, but better, 10.30 at 130 mph.

Sure, there's plenty left in the Cobra, and Smith managed to take down the top GTO that day at Gainesville Raceway. What's even better is how much more he enjoys the car now.

"I've driven it around for about a week, and it's pretty neat," he says. "It sounds completely different, and I have lots of problems with the street tires now that the torque down low has increased so much."

Mach 1 ECM SYM2
Dipstick Tube XR3Z-7A228-BA
Dipstick XR3Z-7A020-BA
Driveshaft Yoke 1R3Z-4841-EA
Shifter Assembly 1R3Z-7210-AA
Trans Shift Cable XR3Z-7E395-AA
and Isolator
Trans Kickdown Cable
Shift Interlock Cable F6ZZ-3F719-AC
Shift Lever Stud E43Z-7B415-A
Plug for the Mechanical
Speed Sensor
Speed Sensor 1L3Z-7H103-AB
Digital Range
Transmission Sensor
Also Called Shift
Position Sensor
(make sure you get
the kit with the
spacers and bolts)
{{{GT}}} 4R75W Transmission
Wiring Harness,
Transmission Cooler,
Lines and Fittings,
{{{Eight}}}-Bolt Flexplate and
Auto Midplate