Since the introduction of the new, late-model Challengers, Chargers, Magnums, and the Chrysler 300s, we have to admit that the performance offered by these vehicles is outstanding. In fact, we've driven, modified and tested several late-model vehicles in the pages of Mopar Muscle, and have always been impressed by their manners both on the road and at the track.
Mopars have long been known for their prowess on the street and drag strip, but while classic Mopars—with their one-piece differential housings—are well suited for drag racing, and do well on stock-car type oval tracks, when it comes to touring or road course racing, they leave a lot to be desired. Conversely, modern Mopar cars are equipped with independent rear suspensions, which make them a great match in terms of braking, accelerating, and taking turns in both directions like is necessary for road course racing. These cars offer a wide stance, and can accommodate big tires both in the front and out back, leaving us wondering why more enthusiasts aren't using late-model Mopars for road racing.
We happened to have access to a body in white Challenger, that doesn't have a VIN or title, so it can only be used as a racecar. The owner decided this car would be used as an open track car. With limited experience in road racing, he enlisted the help of Razor's Edge Motorsports in Pompano Beach, Florida, to help with the build. Razor's Edge is a big supplier of late-model Mopar aftermarket products, including a whole list of suspension components for the new Dodge Challenger. Further, Razor's Edge played a big role in building a Dodge Challenger for the Grand-Am class of road racing, making them a great choice to assist with this build.
Consulting with Paul and the crew at Razor's Edge, it was decided that since the body in white comes as just a body shell, that we should start with the suspension and chassis to give the car a solid foundation. Razor's Edge suggested starting at the rear, and secured a rear suspension cradle for the Dodge. Knowing that a stock differential that comes in the new Dodge Challenger (and other LX platform cars) can be a weak link in high-powered applications, Dynatrac developed their Pro 60 IRS components to turn this weak area into one part of the Challenger that the owner will never have to worry about breaking.
The Dynatrac Pro 60 IRS center section is a custom cast, high-strength nodular iron housing, based on the legendary Dana 60 differential. The housing is a direct bolt in, and is available with multiple gear ratios, from 3.54 to 7.17, and multiple options in terms of internals. For drag racers, the Pro 60 IRS can be fitted with a spool, and for street or road course enthusiasts, a Detroit locker, Truetrac, or even air or electric lockers are available. For this application, the owner chose an Eaton Truetrac, with a 3.73:1 gear ratio. The Pro 60 IRS comes with 35 spline inner stub shafts, and he also chose their high-strength chrome-moly axle shafts featuring high-torque CV joints and 35 spline outer stub shafts and hub bearings.
This month we build and install a Pro 60 IRS differential and axles from Dynatrac Performance.
The Dynatrac Pro 60 IRS is much larger and more durable than factory or even aftermarket IRS center sections for late-model Mopars. The Dynatrac parts are all made in the U.S.A., and feature a one-year limited warranty. The Eaton Truetrac offers maximum traction while still allowing some slip for cornering, and is known for quiet, smooth performance. With helical cut gears, the Truetrac also has no wearable parts, so the unit requires no maintenance. For the do-it-yourselfer Dynatrac also offers the unit as a housing with stub shafts only, making it easy to custom build the centersection to your specs.
Installing the Dynatrac Pro 60 IRS is easiest with the rear suspension cradle dropped from the car. If you're installing the Pro 60 IRS in a complete car, dropping the rear cradle is an easy task, and with the cradle out of the car, it's a good time to install additional aftermarket suspension components.
Razor's Edge offers a ton of parts designed to stiffen the chassis of late-model Mopars, and also manufactures parts specifically intended to enhance the handling of these cars. During assembly, this car also received billet tension and adjustable upper control arms from Razor's Edge. The tension arms feature an 85 durometer bushing on one end, for less flex and distortion, and a fiber reinforced bushing on the other end. Tested to over 60,000 psi, these tension arms are more than twice as strong as factory arms, and lighter as well. The adjustable control arms are a proprietary design, incorporating shims. The adjustable control arms are manufactured from 6061 billet aluminum, and come with a set of shims instead of threaded adjusters, allowing easy adjustment without the wear associated with the axial loading of threads. These parts will allow the user to align the rear wheels of their car for any track condition.
PRICE TAG Dynatrac Pro 60 IRS complete with axles $6,286.00 Razor's Edge Billet Rear Tension Arms $349.00 Razor's Edge Adjustable Rear Control Arms $699.00 Eaton Detroit Truetrac for Dana 60 (separate) $539.97
1. The body-in-white Challengers are production cars that were plucked from the assembly line prior to being fully assembled. Therefore they don’t have any suspension, wiring, plumbing, interior, or glass, nor do they have an engine or transmission. In our eyes, this is a perfect starting point for an open track road race car.
2. Razor’s Edge suggested starting with the rear suspension and differential. Late-model Mopars incorporate an independent rear suspension, making them ideal for thandling, and the Pro 60 IRS replaces the stock center section with one based on the super-tough Dana 60.
3. The Pro 60 IRS is centered around a custom nodular iron housing, with 35-spline chrome-moly inner stub shafts.
4. To fill the Pro 60 IRS the owner chose an Eaton Detroit Truetrac limited slip differential. The Eaton Truetrac is known for maximum traction, while still offering quiet and smooth operation. Even better there are no wearable parts so maintenance is easy.
5. Dynatrac assembled the differential using the Eaton Truetrac unit and 3.73 gears. Dynatrac offers multiple options from spools to lockers, and gear ratios from 3.54 to 7.17. They also offer the Pro 60 IRS as a housing with stub shafts only, allowing the builder to custom tailor the differential to his or her needs.
6. Dynatrac also offers high-strength chrome-moly axle shafts with heavy-duty CV joints, along with 35-spline outer stub shafts and hub bearings. This upgrade will ensure that there is no need to worry about the differential of the Challenger, no matter how much power the soon-to-be-installed late-model Hemi makes.
7. The rear cover allows the Pro 60 IRS to be directly bolted into late model Mopars, and the unit has provisions to drain and refill the differential for easy maintenance. This unit is larger and heavier than a stock differential, making it much stronger than even aftermarket factory style center sections.
8. Installing the Pro 60 IRS is easiest with the rear suspension cradle removed from the car. With the factory center section removed, the Dynatrac unit simply bolts directly in place using the hardware provided by Dynatrac. With the IRS installed, the Dynatrac axle shafts can be bolted in. These axle shafts are included with the Pro 60 IRS kit, and feature heavy duty CV joints and 35 spline outer stub shafts and bearing hubs.
9. A drawback of the Challenger’s factory rear suspension is that the wheel alignment is not adjustable. Now’s the perfect time to upgrade the suspension with new billet-aluminum pieces. These tension arms offer heavy duty bushings, and are more rigid than the factory arms, meaning less flex in the rear suspension. Upper control arms from Razor’s Edge Motorsports incorporate aluminum two-piece arms, with laser cut steel shims for easy adjustment in half-degree increments. These are quality parts that look and perform great, bolt right in place of the factory arms, and will be a huge help tuning the suspension once the Challenger gets to the track.
10. The rear suspension cradle is now assembled.
