The muscle cars built by Dodge and Plymouth have always had a very devoted following and a style all their own. Home to Hemis and Six Packs and clad in colors like Curious Yellow and Plum Crazy Purple, they just scream muscle car. Yet, despite competing next to Camaros and Mustangs in the old SCCA Trans-Am series, and rocking NASCAR with Hemi Chargers, Super-birds, and Daytonas, they never really caught on with the general hot rodding public as performance-handling cars. That’s a shame, because they have some real potential.
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Mopar muscle cars have some unique front suspension features. At first glance, the suspension bears a passing resemblance to that used by Ford but there are some major differences. The most obvious is the use of torsion bars rather than coil springs. Torsion bars have been used with great success on everything from Porsches to the M1 Abrams battle tanks. The torsion bars interface with the lower suspension arms, so they are the weight bearing arms, which is the opposite of the Ford design. A wide assortment of torsion bar rates is available direct from Mopar Performance and also from companies like Firm Feel. These range from drag race (very soft) to rock-hard road race rates. Due to the mounting format of the Mopar torsion bars, they’re all adjustable for ride height, which is a feature all the other muscle car makes have to go to the aftermarket for. This makes selection much easier because ride height isn’t part of the selection process. They’re sold by bar diameter and generally .92- to 1.06-inch-diameter bars should be used for street touring to Pro Touring applications.
Tubular upper A-arms are as popular for Mopars as they are for all the other muscle cars, and for the same reasons. Properly designed upper A-arms let you crank some much-needed positive caster and negative camber into the front end, which improves road feel and performance. Fixed-length offset arms are available from Firm Feel. Single-adjustable arms are available from Reilly MotorSports and Hotchkiss among others, but they require disassembly to adjust. Double-adjustable arms with hard-anodized aluminum hex adjustment sleeves are available for B- and E-bodies from SPC. These do not need to be disassembled to adjust and have a larger range of adjustment than the aforementioned single-adjustable arms.
It’s also important to note that Mopar arms are particularly flimsy. They flex so much it actually affects dynamic camber and caster! That makes replacing the stock A-arms almost a requirement for good and consistent handling.
The geometry of A-, B-, and E-body Mopar front ends is much different than that of their Ford and GM counterparts. Rather than having a pronounced positive-camber curve in bump, theirs is negative. Rather than the roll center being much too low, it’s actually too high. That means they have a whole different set of issues. On paper, they should handle quite a bit better than some of the other popular muscle cars. But, in factory form, they seldom do. This is due mainly to the extremely soft torsion bar rates and shock dampening, or lack thereof, of the factory suspension components. They also used small sway bars, if they even used sway bars. Because of this, Mopars respond exceptionally well to tuning.
Body roll is inhibited by the high roll center, but the roll center is high enough so suspension jacking can be excessive. Sway bars can help with this, but combined with a high RC they can induce understeer. That makes a rear sway bar even more necessary than normal for a well-balanced handling platform. An adjustable-rate rear bar would be an exceptionally good idea. With the proper application of higher torsion bar tension and stiffer sway bar rates, along with improved dampening and alignment specifications, great gains in drivability and handling can be had. You won’t get road racing car handling from this type of combination, but you can make a very significant improvement and produce a really fun and competent street performance car.
The alternative to modifying the factory suspension is to go to an after-market K-frame with an all-new suspension attached. Be cautious, since some of the aftermarket K-frames maintain stock geometry and are intended only for weight reduction. These are primarily designed for and used in drag racing applications. The best known K-frame suspension conversion is the “Alter-Ktion” system from Reilly MotorSports, which has been in production for a decade. It’s proven to be simple and effective, using coil-over shocks, boasting tubular A-arms top and bottom, and bolting to unaltered frame rails. Another alternative is the “Series II” package made by XV Motorsports, which takes the curious approach of improving Mopar handling with a generous dose of factory Chevrolet parts—aluminum spindles and lower A-arms sourced from the C5 Corvette. By all indications this looks like a well-designed package because the C5 Corvette is a very well-handling car.
The rear suspension on Mopar muscle cars is a pretty typical parallel-leaf-spring design. The normal technologies apply. Mopars do have a few unique features when it comes to the rear suspension, though. See Chapter 2 for more details than I cover here.
First are the legendary “Super Stock” springs. These were designed by Chrysler specifically for drag racing. They feature more forward leaf bias than typical springs would, to provide better traction. It’s not unusual to see them being run with spring clamps on the front half of the leaf pack and no clamps on the rear half. As discussed previously, this is not ideal for handling. It decouples the rest of the spring pack from the main leaf in droop, or for the inboard spring in roll while cornering. This decoupling adversely affects cornering and braking, so make sure there are clamps on both ends of the spring packs for all-around performance use. The forward leaf bias isn’t a bad thing, as long as the springs provide enough roll rate for a handling application and otherwise fit into the total package.
Mopar Performance offers a kit to move the leaf springs inboard for more tire clearance. This is fine, but be aware that this adversely affects the spring’s motion ratio in roll, so more spring rate (or sway bar roll rate) may be necessary than would otherwise be required.
An unusual Mopar rear suspension option is the use of a tall, adjustable pinion snubber to enhance traction. This, in effect, uses the pinion housing of the rear end like an ultra-short torque arm or slapper bar. It’s actually pretty effective, as many Mopar racers have proven over the years. It should be used with caution, though; by design, snubbers add binding and effective spring rate. A pinion snubber has much less affect on roll than a comparable bolt-on slapper bar arrangement. But it can still have an unsettling effect if and when it makes contact in mid turn and increases the effective spring rate of the rear suspension. So take advantage of an adjustable pinion snubber at the drags, and then adjust it down and out of the way for street driving and any type of handling use.
Another cool feature of Mopar leaf springs is how their front mount can be replaced with a heavier-duty reinforced mount, a mount that allows for specific aftermarket shorter springs, or even mounts with more than one mounting hole. This last option allows you to adjust the side-view geometry of the springs by raising the front of the spring. Doing so lowers the car roughly 1 inch, and also improves off-the-line traction.
Like many other popular muscle-car platforms, rear suspension packages are available to replace the leaf springs with links and coil-overs or air bags. Some of the most popular are the RideTech AirBar and Chassisworks G-Bar, which are related systems, and the Street Lynx from RMS. These are converging four-link systems.
Mopar sway bars are also a little different than those of other muscle cars. For starters, a lot of Mopars didn’t come with sway bars from the factory. This fact contributes to the reason they’re not often associated with performance handling. Secondly, those cars not equipped with sway bars don’t have any provisions to mount them! Naturally, the aftermarket has stepped in and made bars and brackets available, but they vary wildly in how well they’re executed. Some of the brackets for the front sway bars appear to be cheaply made. Look for beefy, clean brackets and bars that don’t compromise ground or tire clearance.
Mopar rear sway bars are typically frame-mounted. That’s a good thing because it makes the weight of the bar sprung weight, rather than unsprung weight. However, some very good Mopar bars are axle-mounted instead to gain more bar-to-tailpipe clearance, extra room for adjustable end links, and multiple mounting points for rate adjustment. Many of the newer rear bars weigh only 8 or 9 pounds, and, because they’re being bolted to a 300-pound rear axle, I’m not concerned about where they’re mounted, just that they work as promised. Of course, I prefer an adjustable-rate bar every time it’s available.
The lack of chassis stiffness reappears again in Mopar muscle cars. Subframe connectors are a must, and are available from Mopar Performance, Hotchkis and others.
Building a Pro Touring-style Mopar may be taking the road less traveled, but that’s often the most rewarding road.
Written by Mark Savitske and Posted with Permission of CarTechBooks