There are a lot of different ways to update the suspension on your muscle Mopar. If you're looking for a complete aftermarket for the front of your ride, there are a couple of choices available for you. For the sake of this article, we wanted to just focus on what can be done to improve handling, while retaining the stock suspension system. In other words, there'll be no mention of coilovers, airbags, or four-links--just the straight-up Mopar design. Lest you think that's boring, consider that there are some very fast Mopars out there running stock-style suspensions.
The torsion bars are as good of a place to start as any. The torsion bar is basically a cleverly designed spring that provides excellent performance from a compact assembly. People might curse torsion bars when trying to install headers, but on the up side, having the torsion bars located low in the chassis reduces the center of gravity, and the torsion bar is also unsprung weight. As a further benefit, the ride height is very simple to adjust with the Mopar torsion bar design.
Changing the bars is fairly easy, once you invest in a torsion bar removal tool. The surface of the torsion bar is highly stressed, so care must be taken to protect the bars while knocking them out, so using a pipe wrench or locking pliers is not a good idea. Replacement bars are available in a range of different spring rates, covering everything from drag racing to street use, to autocross and road racing. The spring rate of the bar is determined by the fourth power of the bar's diameter, so even a small change in size will make a large increase in its spring rate.
The factory offered several sizes of torsion bars for each body line, according to the intended use of the car. The softest bars were used in light duty cars (read Slant Six–powered commuters), while the biggest bars were offered as part of heavy-duty suspension packages, or with optional engines. It is still possible to find original/used torsion bars at swap meets, but since aftermarket bars are readily available, it is probably easier to just order new ones. For example, Performance Suspension Technologies (PST) offers torsion bars for A, B, and E-Body cars in sizes from .880 to 1.180-inch diameter. This might not seem like a huge difference in size, but the spring rate on the 1.180-inch bar is more than three times as great as the spring rate of the .880-inch bar. So be careful when you order torsion bars, as too much of a good thing can definitely spoil the ride.
Spring rates for torsion bars are measured at the lower ball joint, so they are representative of what the wheel sees. On cars with coil springs, the wheel rate is much less than the spring rate due to the geometry of the suspension. So don't try to compare a 200 lb/in torsion bar with a 200 lb/in coil spring, unless you know you are comparing wheel rates. A handy rule of thumb when picking a bar is to select one with a wheel rate that is 1?10 of the front-end weight of the car. For instance, a 3,600-pound car with 50 percent of the weight on the front end has a front end weight of 1,800 pounds. A good starting point for the wheel rate would be 1,800/10, or a 180 lb/in bar. If you're working on a B-Body, the closest bar available is the 1-inch bar with a wheel rate of 186 lb/in. For an A-Body, the .920-inch bar at 150 lb/in is probably the best choice. The next size up is the .990-inch bar at 200 lb/in, which is probably a tad too stiff for most folks. Remember, A-Body bars are shorter than B-Body bars, which makes them stiffer. A fairly common question people have is if they can use the drag race torsion bar on street-driven cars. Obviously, this low spring-rate bar is going to have difficulty controlling a heavy car while cornering, so you typically wouldn't want to use it for any type of daily driving. The real reason to avoid such a bar on the street has to do with the fact that this bar could be dangerously overloaded in such situations. Remember, the torsion bar is nothing more than a spring. And much like a valvespring that is overloaded, an overloaded torsion bar can fail. With a spring rate of only 92 lb/in of travel, the drag race bar has to be severely twisted to support the nose of a heavy car. Such a dramatic amount of twisting sends the internal stresses sky high. If the car hits a large bump and bottoms out, this overloaded bar could snap from the stress. Even if it doesn't snap right away, the life of such an overloaded spring is going to be fairly short.