Muscle Mustangs & Fast FordsHow To Drivetrain
Installing a Performance Automatic 4R70W Transmission in a 1999 Ford Mustang GT
Plug & Play 4R70W trans swap: Performance Automatic helps us shave serious e.t. without adding more power thanks to a built trans and an aggressive stall
The moment our New Edge GT launched at Auto Club Dragway shortly after we installed this month’s drivetrain mods, we knew it was going to be significantly faster. How could we tell? Because with the stock transmission it would barely lift the nose at launch as the Two Valve struggled to pull all that iron out of the hole in search of enough rpm to make things happen. But now, thanks to our latest modifications, the GT was coming out with the nose far higher than a stock Two Valve has any right to.
Let’s be honest. Stock automatic-equipped Two Valves aren’t known for their out-of-the-box performance. The stock converter doesn’t play well with the lack of low-rpm torque, and the slushy shifts mean that it spends considerable time between gears rather than driving forward. There’s no way around it—most stock 4R70W-equipped, light bolt-on New Edge GTs cover the quarter-mile in the low 15-second to high 14-second range with so little drama you could sip a latte and enjoy the scenery during the pass. This isn’t to say that auto GTs can’t be made into capable cars; it just takes the right recipe of aftermarket parts to unlock their performance. And in case you were wondering, that’s exactly what we’re doing here—starting with a transmission upgrade.
Say what? Yep, we’re not starting with more power because as any longtime gearhead will tell you, there’s lots of performance to be gained from an automatic transmission upgrade. Also, stock automatics tend to fail in short order with the addition of more power, so if we start by building a strong foundation we’ll have less problems down the road.
Harvey Baker of Performance Automatic says, “A well-built automatic transmission and properly spec’d torque converter can really wake up a car. The transmission can shift gears faster and hold more power, the upgraded components can withstand the converter being locked under WOT, and the performance converter gets the car up into the powerband much sooner.”
As many already know, the 4R70W automatic transmission is legendary for its strength when outfitted with the right aftermarket parts. Many hardcore drag racers have put more than a thousand horsepower through properly built examples without problems. This legendary four-speed automatic with overdrive has been in the Mustang since 1996, but was later updated in 1999 and remained relatively unchanged until it was replaced with the later 5R55S transmission in the S197.
As solid as the aftermarket can build 4R70Ws, it can’t be built to withstand the rigors of big power by just anyone. Secondly, in stock form it is more a slushbox than a gear grabber.
“The stock 4R70Ws are great transmissions, but they can’t handle big power or shift quickly since their design parameters were for a stock Mustang,” says Baker.
OK, so the stock box can’t handle big beans, but who are you going to trust to build a bulletproof version? In our case, the decision was simple: Performance Automatic. The company has been building transmissions for over 30 years. After getting a start in the transmission service business, Performance Automatic’s reputation for building wicked performance boxes not only made it the go-to place to buy a race-ready transmission, but it spawned the transformation of the company from the service side to production.
Baker says, “We offer several levels of transmissions, from performance replacements with a one-year or a lifetime warranty on up to full competition-level transmissions that can handle well over 600 hp.”
After speaking with Performance Automatic about our long-term goals and the intended use of our New Edge GT, the company spec’d a PA45101C-46L, which is a competition-level 4R70W transmission kit that came with everything necessary to get our Two Valve rolling.
“Our competition 4R70W transmissions come with all the right parts to survive track abuse while also allowing enough civility to be driven on the street in a performance application,” Baker explains.
Inside the case you’ll find plenty of top-shelf bits that are built to handle big power, like Raybestos Racing clutches, heavy-duty servos, a hardened stub shaft, high-performance bands, drums, and a diode, along with a street/strip valve body.
“We choose a specific combination of parts for our transmissions based on the intended use,” says Baker, “and in the case of the transmission for this New Edge GT project, our competition transmission with the street/strip valve body was chosen because it will hold up to 650 hp and plenty of track abuse without having punishingly hard shifts on the street.”
Believe it or not, a well-built performance automatic transmission is only a piece of the performance pie. It also needs to work alongside a set of quality components spec’d to complement one another.
Competitive drag racers know a quality torque converter is crucial to maximizing performance, but most hold this secret close to the vest. Baker says, “Specing the right converter to the application is important since the right unit can really wake up a car and get it out of the hole a lot faster.”
It’s no secret that a torque converter can be worth up to 2 1/2 times the engine torque thanks to torque multiplication. That means the 302 lb-ft of torque our Two Valve is making at the crank could be over 600 lb-ft at the input shaft of the transmission as it launches from the starting line with a higher-rpm stall converter. OK, so this torque multiplication is only momentary as the speed of the turbine and impeller inside the torque converter equalize and the converter reaches coupling speed, but at the given stall of the converter, the torque multiplication is greatest. Within reason, the higher the stall speed, the greater the torque multiplication.
“The factory stalls are roughly 1,100 rpm, which means the motor isn’t allowed to spin high enough into the powerband to make significant power before it’s loaded by the drivetrain, causing a sluggish launch. But get that stall speed up around 2,800 to 3,000 rpm and the Two Valve really comes alive off the line,” Baker says.
So that’s exactly what we did, with a PA45203 10-inch, triple-disc converter with a billet cover. In its current state with our mods, it stalls to roughly 2,800-3,000 rpm, but as we increase power that will change.
“We spec’d the converter with the end goal of more power, but the advantage of this unit is that we can modify the stall speed to suit any future mods you should add,” Baker says.
1. Performance Automatic (PA) takes the guesswork out of swapping in its built 4R70W transmission. The transmission is good for over 650 hp thanks to a Smart Pack, which comes with everything needed to turn power into forward motion.
2. PA helped us spec a 10-inch, triple-disc converter with a 2,800- to 3,000-stall speed. The unit is also upgradable should our future mods take us in a different direction.
3. Although we didn’t utilize the included PA transmission cooler, it is a killer nine-row unit that also comes with stainless steel braided lines.
4. See the sidebar for the full story on the MSD Atomic transmission controller that comes with the Smart Pack, but in brief it allows those with SN95s and Fox-bodies to swap to the newer 4R70W and have full control over the transmission with a few pokes of some buttons.
5. The midpipe and driveshaft will need to be removed to gain access to the stock 4R70W transmission. Thankfully our GT was in good hands at GTR High Performance, where Will Meza, Ricardo Topete, and the crew of Mustang gurus made short work of the swap.
6. Next up, the external connectors and the gear selection control cable need to be disconnected. The oil also needs to be drained from the transmission by removing the oil pan.
7. With everything disconnected, the GTR crew carefully secured the transmission to a trans jack with straps and a chain and then carefully lowered it from underneath the car.
8. PA literally thought of everything with the Smart Pack. PA stressed the importance of a properly made starter-index plate since poorly made units can cause all sorts of problems. Thankfully PA includes a quality unit in the kit. Before sliding the torque converter onto the input shaft of the PA 4R70W transmission, be sure to apply grease.
9. The PA triple-disc clutch needs to be filled with the included oil before being installed onto the transmission.
10. Ready for blastoff! It’s time to go skyward with the built PA transmission, but not before it is securely strapped to the transmission jack.
11. All of the speedometer and auxiliary connectors come with plugs from PA; you’ll need to remove them before reconnecting the OEM plugs, harnesses, and connectors.
12. A pry bar or a long flat-blade screwdriver is helpful when spinning the torque converter in order to tighten all of the bolts to the flex plate.
13. Make sure you have the gearshift selector cable in the right orientation before connecting it to the PA transmission or else the gear selection won’t be accurate.
14. PA includes a dipstick and filler tube in the Smart Pack. After the installation is complete, don’t forget to fill the new transmission with the included oil. Then it’s time to burn some rubber.
OK, so we’ve got a killer transmission and a proper converter, but there’s still another key component to the drivetrain upgrades: a proper installation kit.
“There’s nothing worse than buying an incomplete transmission kit that lacks the proper components to make it a bolt-in installation, which means you’re stuck waiting on individual parts and making unplanned trips to the local parts house,” Baker said.
In addition to killer components, Performance Automatic also prides itself on selling complete kits that literally have everything needed to get swap in a 4R70W (and other transmissions) into Fox-bodies, SN95s, New Edges, and other fast Fords with Performance Automatic’s innovative Smart Packs.
Baker says, “We’ve gone to great lengths to include everything the end user will need to install the transmission, like a properly sized starter index plate, the dipstick that Ford no longer makes, a transmission mount, a nine-row transmission cooler with steel braided lines, the filler tube, fluid, and literally everything needed to make the installation easy.”
That’s right; not only does Performance Automatic include everything needed to install the transmission in your Mustang, but thanks to the help of an included MSD Atomic transmission controller (see sidebar) and the supplied conversion parts, you can also replace the T5 or AOD in your older Mustang with a newer 4R70W.
“This can be a great upgrade for people with older cars who are either looking for a better street transmission with a lockup converter and a tall overdrive or looking to put big power into their Fox-body or SN95,” Baker says.
Usually the small details of getting an upgraded transmission into your Mustang are left up to the end-user, but in this case, Performance Automatic makes the swap easy.
The best parts are nothing without a tidy install. As we’ve done with many builds, we turned to the West Coast Mustang gurus at GTR High Performance in Rancho Cucamonga, California, for help. Will Meza, Ricardo Topete, and the crew of Mustang experts at GTR made short work of removing the stock stuff and installing the performance goodies.
In under a day the crew had completed the install and made mention that the Smart Pack made the installation much easier. Since our New Edge already had a 4R70W from the factory, we opted not to use the included transmission cooler at this time, nor did we need the MSD Atomic transmission controller since we had a previously installed DiabloSport Programmer that allowed us to dial in the transmission. But had we lacked the programmer, the Performance Automatic install would have been a plug-and-play affair, even if we were updating an older Mustang with a newer 4R70W.
Track thrash and driving impression
From the moment we spun the New Edge down the street after GTR High Performance was done with the install, we knew the GT was going to perform much better at the strip. The Performance Automatic stall converter got the motor into the powerband much sooner. The transmission not only ripped off shifts with authority, but with some tuning we were able to dial down the part-throttle shifts so it would be firm without being harsh. During daily driving the larger stall requires a little more throttle to get moving, but once under way it behaves much like the stock unit, and the converter locks up nicely on the freeway for good fuel mileage. The offset is that we can now smoke the tires with the stab of the gas, a feat the stock setup would never achieve—and all without increasing horsepower.
Shortly after the install we paid a visit to Auto Club Dragway in Fontana, California, for some track time to see what our drivetrain mods were worth in the way of e.t. and mph. To be fair, while we never baselined the car, it is safe to assume it was in the low 15s or very high 14s at best, since it was stock save for a CAI, mufflers, and a tune prior to these upgrades. As mentioned, the minute the GT yanked the front bumper in the air on the green bulb, we knew it was going to be good, but we could have never guessed it was going to run a 14.28 at 94 mph. Seriously, it launches considerably harder than you’d expect a bolt-on Two Valve would, it rips off shifts with quickness, and the acceleration only tapers in the upper gears when (as expected) we run out of steam. To run low 14s in an intake-and-exhaust–equipped Two Valve with an automatic is nothing short of impressive in our book, and it’s only going to get better with the planned mods.
We’ve not only laid the foundation for big power by building a bulletproof drivetrain, but we also improved performance by a considerable margin. Stay tuned. We’ve got some big plans for our automatic-equipped GT.
MSD Atomic Transmission Controller
In the high-performance community MSD is known for making some of the best ignition systems, but in recent years the company has also applied its expertise to EFI systems and transmission controllers. That’s right, the MSD Atomic transmission controller has the ability to fully control many transmissions like the Performance Automatic 4R70W, giving enthusiasts the ability to put the electronic-controlled transmission into an older chassis that didn’t come so equipped and then have full control over the transmission’s tuning. Want to tweak shift points, shift firmness, and torque converter behavior? Want to switch between auto-shift or manual mode? The Atomic unit can do it all. It also comes preprogrammed with the ability to monitor the transmission in real time. The easy-to-use interface makes getting started and getting the most of your automatic transmission tuning easy.
The Atomics are offered as freestanding controllers or with a harness. In the case of our Performance Automatic Smart Pack, the MSD Atomic EFI controller and harness come as part of the kit, so upgrading your Fox-body or SN95 to a 4R70W is a simple affair. Ah, the wonders of technology.
Axle-Exchange Aluminum Driveshaft
As part of the drivetrain package we also ditched the heavy and equally weak stock driveshaft for a feathery yet strong aluminum driveshaft from Axle-Exchange. This lightweight unit came cut to the exact dimensions, is high-speed balanced for the top-speed blasts we’ll be hitting this summer, and is built to handle all the horsepower and traction we plan on adding. Yep, not only will we be adding big power, but we’ll be slicking down at the track and letting this Two Valve eat . . . and the last thing we need to worry about is a stock driveshaft snapping in half and tearing through the floorboard at high speed. We consider a quality aluminum driveshaft from Axle-Exchange cheap insurance.