It’s been well documented that the Coyote engine really responds to forced induction. Even on low boost, just bolting a blower up to Ford’s modular 5.0-liter mill can really transform the way that DOHC V8 behaves. But as the horsepower goes up, so does the stress on all of the components that grunt gets sent to.
With an L&R short-block, a VMP Performance Gen2R supercharger, JBA long-tube headers, cat-less mid-pipes, Comp Cams Stage 2 camshafts, forged pistons and connecting rods, Boss 302 cylinder heads and a few other goodies, this 2013 Mustang GT is putting down about 800 horsepower to the wheels, a combination that puts this pony in the nines at the drag strip on competition rubber.
But now that it’s putting out more than twice the power that it offered in stock form and it’s getting all that grunt to the pavement through those gummy Mickey Thompson drag radials, it’s clear that the stock rear end is being asked to put up with abuse that Ford never designed it for.
In the interest of not scattering rearend components into the staging lane the next time we line up at the lights, we’re turning to Moser Engineering for a custom 9-inch rearend that’ll be future proofed to 1,000 rear-wheel horsepower. Here we’ll discuss the particulars of the new rear with the experts at Moser, and go over how to correctly spec out a custom assembly for a specific application, talk differential lubrication with the folks from Driven Racing Oils, and upgrade the rear suspension with an anti-roll bar kit from BMR Suspension.
A Robust Rearend
While increased strength might be the most obvious reason to swap out the OEM rearend for an aftermarket piece, the benefits aren’t limited to just beefed-up durability. Still, stock rearend failures are often what initially sends enthusiasts Moser’s way.
There are a few reasons for switching to a fabricated 9-inch from a factory housing. — Jeff Anderson, Moser Engineering
The most important thing to consider first is your intended use for this vehicle. — Jeff Anderson, Moser Engineering
“The Moser M9 housing itself features a geometric design to distribute load forces evenly to the face plate and the axle tubes,” Jeff added. “The M9 fabricated is not assembled from individual triangles but from a single, laser-cut piece of steel that is then shaped on a press to allow a perfect geometric alignment that could never be matched by welding individual pieces together. This allows a direct transmission of load forces through the housing to the face plate. We also add Internal bulkhead style gussets so that the tubes and housing are rock solid, as well as oversized fill and drain plugs also allow ease in maintenance for any serious racer. And when comparing equal size splines on the axles, you can actually lower the weight of the rear when going to a fabricated M9 design over the stock unit.”
Of course choosing the proper specs for your application when ordering a custom rearend is particularly important if you want to get the most out of this modification, and Jeff offered some advice in that regard as well.
“The most important thing to consider first is your intended use for this vehicle,” he said. “Is it a street cruiser, a road course racer, a strip-only car, or a little of everything? You will also need to think about the differential, wheels and tires you’re going to run and also brake options. With that information you can then put together a plan for the spline count needed along with bolt pattern and stud size. You also want to consider the axle bearings you should use, along with any ABS options you may need to retain, then you look at the carrier or differential options and case type from aluminum to nodular depending on your needs, gear ratio and type of gear, and finally the yoke size.”
It may seem like a lot of info to put together into an effective plan, but Jeff is quick to point out that the experts at Moser — who’re racers and street-rod enthusiasts themselves – are just a phone call away if you need some assistance with zeroing in on the most ideal setup for your application.
“Gear oils utilize a completely different chemistry than motor oil, and that is because the sliding loads in a rear gear are much higher than in any engine,” says Driven’s Lake Speed Jr. “As a result, the level and type of extreme pressure additives must be tailored to the needs of a differential. This is especially true of a hypoid-style rear gear. Because NASCAR has mandated Ford 9-inch hypoid style rear gears for decades, we have over a million race miles of experience with hypoid gears.”
He says that most applications can run a 75W-90 synthetic after the gears are broken-in, and just like your engine, you should be using a break-in gear oil to break-in any new differential or manual transmission.
“After break-in, a 75W-90 is good up to about 1,000 horsepower. A 75W-110 is good up to 1,500 horsepower and a 75W-140 is good beyond that,” he added.
With that experience under its belt, Driven has been able to hone in on the specific lubrication attributes that are best suited to the demands asked of the rearend assembly in a performance setting, especially those using the hypoid-style gears with an offset pinion gear. These arrangements allow for larger, more durable gears that run quieter.
“The key lies in balancing traction and extreme-pressure/anti-wear protection,” Lake explained. “While hypoid gears need a lot of extreme pressure and anti-wear additives, these additives can actually increase friction, which can cause a whole other set of problems, so the formulator must balance the needs to reduce friction and provide excellent wear protection. Friction and wear are not two sides of the same coin — just because you reduce wear does not mean you reduce friction and vice versa.”
Planting The Power
While we’re in the process of swapping out the stock rearend for the Moser unit we’re also upgrading the rear suspension with an Xtreme anti-roll bar kit from BMR, as the stock sway bar can no longer be used with the new rearend without additional legwork. Along with being compatible with the new differential hardware, the BMR bar (PN XSB011) features some design improvements over the stock piece that should help keep the rear suspension in check during hard launches.
“The BMR XSB011 replaces the stock sway bar with an anti-roll bar that’s better suited to this kind of performance application,” BMR’s Mustang suspension specialist Kelly Aiken said. “It also eliminates the need to purchase and install additional components like our sway bar relocation kit (PN SRK001), and the XSB011 is unique in that it is the only S97 anti-roll bar of its kind with Delrin bushings, which are much stiffer than a poly bushing and typically last a lifetime.”
Offering more than a 400-percent increase in stiffness compared to the OEM bar, the BMR bar also helps plant the power more effectively by eliminating the body roll that the S197 three-links suffer from.
So essentially what the BMR anti-roll bar will do is keep the suspension consistent side to side. — Kelly Aiken, BMR Suspension
This motion causes the rear passenger side suspension to compress, which actually takes force away from the tire in this scenario. On the driver side when the body rises it is planting the tire, but if it rolls too much, it will unload and shock the suspension.
“So essentially what the BMR anti-roll bar will do is keep the suspension consistent side to side,” Kelly added. “This ensures that the driver-side tire plants smoothly and does not over extend, and the passenger side will not squat as much, which takes away force and unplants the tire.”
With the new rearend assembled, the car up on the lift, and the rear wheels removed we got to work removing the old components. Since we opted to use Moser’s Performance Dynamic Rear Drag Brake Kit we wouldn’t need to transfer over any components from the old rearend to the new one, so all of that hardware was removed as one piece.
Since the driveshaft came out for the rearend swap, we opted to fortify this as well, replacing the stock unit with a beefier piece from JE Reel, along with a driveshaft loop from BMR. First the new Moser rearend needed to be installed though, followed by the new brakes.
With the brakes installed on the new rear, we hooked up the new driveshaft as well as the new driveshaft loop.
Next we turned our attention to the installation of the BMR anti-roll bar kit. To open up more room to work, we removed the mufflers.
All in, this setup should not only provide much more strength and durability than the stock rearend, it should also yield improved e.t.’s by more effectively putting the power to the ground and offer more consistency in its performance overall.
Ready to step up your rearend game? Moser Engineering, BMR Suspension, and Driven Racing Oil have the stuff you need to lower those e.t.’s while ensuring that you won’t be “that guy” with the detonated differential at your next drag night. Stay tuned…