Images: Blow By Racing

Ever since Tremec’s T56 appeared in the 2003 Cobra, Mustang fans have been enamored with the six-speed transmission. We’ve wanted to swap a six-speed into every Mustang since. Even if the Mustang came from Ford with a six-speed already in it, we’ve looked to Tremec again to bolt in the bad boy we discuss here, the Magnum XL.

As we’ve previously covered, Tremec’s Magnum six-speed is probably the baddest out-of-the-box, factory-style manual transmission you can put in a Mustang, and when Blow-By Racing decided to add one to this ’15 Mustang GT, we had to follow along.

The Magnum XL is versatile, tough, and with two overdrive gears, economical from a fuel usage standpoint, as well. The best thing is, though, Tremec has two versions of the transmission, which makes it possible to bolt it into any late-model Mustang.

The Magnum transmission was initially designed to fit in a Fox Mustang, and have the shifter in the stock location. Since the Fox and SN95 chassis are basically the same, that application didn’t need a redesign. However, when the S197 chassis debuted, the shifter location was moved back, when compared to a Fox/SN95 shifter location, and the S550 floor pan is roughly the same as the S197. Therefore, the original Magnum wouldn’t work with the new cars.

During all this, Tremec was also contracted to build the Shelby GT500’s TR-6060 six-speed transmission. The TR-6060, for all intents and purposes, is a Magnum with a remote shifter set-up for the extended shifter location in the newer cars. Tremec’s answer for this was to extend the tail housing on a Magnum transmission, and call it a Magnum XL, for extended length. The extended tail housing made it possible to install a stronger, solid-mounted shifter, six-speed transmission into the S197 and S550 chassis.

Why Make the Swap

There are several reasons for swapping a Tremec Magnum XL into your Mustang. Many Mustang enthusiasts have never cared for the remote shifter arrangement, which is most often the reason people switch to the Magnum XL. Plus, for pre-’11 GT owners, many longed for a six-speed transmission. And for ’11-up owners, many didn’t care for the Getrag MT-82 six-speed transmission that came factory. This author, having driven many ’11-’14 Mustang GTs, felt that in town you were always shifting the car. The transmission gearing lends itself well to drag strip action since the rpm doesn’t drop on shifts, but in town it seems you spend much of your time shifting the Getrag. For Blow-By’s Chris Jones, he says, “We’re trying to keep the car as a street car with plans for big power so we decided on the Magnum XL.”

First things first, the factory Getrag MT-82 transmission needs to come out. The shifter, and all its bracketry must be loosened, as well. And of course, the center part of the exhaust must be removed. A transmission jack makes this job easier than not using one. Loosen all the bolts for the transmission, saving the transmission crossmember bolts for last. Then you can use a transmission jack to support the transmission while loosening the transmission crossmember bolts.

With the revised gear ratios in the ’11-up Shelby GT500, you didn’t have to spend so much time shifting. You could leave it in 3rd, or 4th gear, and motor through town. The transmission gearing would allow you to leave it in a certain gear even if you had to slow down, and accelerate again.

However, most complaints we have heard is that of the Getrag not standing up to aggressive driving like what takes place at the drag strip. Since so many Mustang owners add power, the Getrag would seemingly check out after being worked over by power adder-equipped ’11-’14 cars. Owners wanted something stronger, and that’s where the Magnum XL comes in. Tremec’s Magnum XL is one of the toughest six-speed transmissions on the market. Thankfully, the S550 floorpan’s shifter location didn’t change. Therefore, a Magnum XL will bolt into a 2015 GT, as well.

The Magnum XL is available in two different gear ratio packages. One is a 2.97/2.10/1.46/1,00/.80/.63 first through sixth gear set, while the other is a 2.66/1.78/1.30/1.00/.74/.50. Remember, a numerically lower first-gear means a higher torque capacity, which ultimately is the Magnum XL’s top selling point.

The latter ratio mimics the gear set found in the 2013-’14 Shelby GT500’s TR-6060. The latter gear set lends itself to a more long-legged driving experience, and manageable fuel economy on the highway. We’ve seen 1,000-rwhp Shelbys get 19 mpg on the highway with the .50 sixth-gear.

Blow-By Racing used an Exedy clutch for the swap. The Magnum XL uses a different spline count than the factory clutch. The Magnum XL uses a 26-spline input shaft so the clutch's spline count needs to mirror that number. The Magnum XL, unlike the TR-6060 has a separate bellhousing so that is bolted on after the clutch and flywheel.

What You Will Need

If you’re reading this, and interested in swapping your Mustang’s MT-82 transmission for a Tremec Magnum XL, here’s what you will need. Of course, you will need the Magnum XL transmission, but you’ll also need a new clutch. The spline count (26) on the Magnum XL’s input shaft is different than the Getrag so the factory clutch will need to be replaced with a 26-spline unit. Plus, if you’re upgrading the transmission, that means you’re upgrading it because there’s increased horsepower over stock, and the potential for track time, so it only makes sense to replace the clutch with a more performance oriented unit.

Just as Blow-By did for this install, it’s a good idea to add an SFI-approved bellhousing. If we’re going for performance, that means aggressive launches will be the usual drill. With the SFI-approved bell housing, we’ve taken safety measures into account when it comes to the swap, and if you plan on going really fast at a drag strip, your car will be required to have an SFI-approved bell housing anyways.

When it comes to the Magnum’s mounting into the S550 chassis, Jones used the 2011-’14 transmission mount, Jones says, “It bolted right up.” Something else to think about with this swap is the speed sensor/speedometer issue. The two transmissions use different methods of vehicle speed. Jones tried a recalculation box, but it didn’t work properly. “The 2015 ECU, I believe, looks at the wheel ABS for the speedometer. MPH was spot-on with nothing additional,” Jones adds.

If making the swap to a Magnum XL, you will also need a new driveshaft. The factory driveshaft, for one, will be too long with the Magnum XL in place. Plus, a vast majority of Mustang owners, even with the stock Getrag in the car, replace the factory two-piece driveshaft with a one-piece aluminum shaft for less weight, which equals improved performance. In this case, though, there’s no questioning it, you have to add a new driveshaft, and an aluminum one-piece design is the way to go. The Getrag uses a flange-style bolt-in arrangement, while the Magnum uses a slip yoke-style attachment. All the driveshaft manufacturers stock what you need to bolt in their aluminum one-piece units.

The Magnum XL comes with a shifter on it from Tremec. You can change it out for a unit you are more accustomed to, or one from the shifter manufacturer of your choice. However, if the Tremec shifter is to your liking, you won’t need to purchase one. Having experienced a Tremec shifter, this author can vouch for the manufacturer’s shifter, but we know everyone has their favorite.

Something else you will need, if you’re doing the swap yourself is a lift, and a transmission jack. Both will make the job so much easier. If you don’t have both, we would highly recommend utilizing a shop to do the swap for you. Back in the olden days, we would simply lift a T5 into place, but neither of these transmissions is a T5. Both are heavier than the old T5. Yes, you can lift the Getrag out of the way and the Magnum XL into place, but trust us, a lift and transmission jack is the way to go here.

Blow-By Racing installed a Dynatech one-piece aluminum driveshaft the same time as the Magnum XL, as well. 'Dynatech was able to make us a custom driveshaft in a timely manner,' Jones says. As you can see by this car's exhaust arrangement, we have a feeling the engine's going to see redline on a regular basis.

After the Swap

So what can you expect from this swap? You can expect increased reliability over the Getrag, a better, more sure-shifting experience, and perhaps improved fuel economy as well. Of course, we doubt you will see much improved fuel economy at first; you’ll be having too much fun with the Magnum XL in place to worry about those MPGs!