A torsion bar is a long round spring steel bar that resists twisting and returns to its original position after being twisted, thus providing a spring action for the car. It is a form of a weight-bearing spring. Torsion-bar suspension systems were used in most Chrysler vehicles of the 1950s, 1960s, and 1970s, Cadillac Eldorado, Oldsmobile Toronado, Packard, and more. They are currently used in trucks and SUVs from Ford, General Motors, and Dodge. Although all of these torsion-bar systems operate basically in the same manner, this book concentrates on the Chrysler-built cars as they are still popular on most drag strips around the country.
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Chrysler had three main passenger car platforms called A, B, and E. The A-Body torsion bars were 35.7 inches long, while the B- and E-Body bars were 41 inches long. For all three bodies, the hex end measured 1¼ inches. Therefore any bar with the same length could be swapped into another car regardless of diameter.
Chrysler A-Body cars with 35.7-inch-long torsion bars include:
1960–1976 Plymouth Valiant
1963–1976 Dodge Dart
1964–1969 Plymouth Barracuda
1971–1976 Plymouth Scamp
1970–1976 Plymouth Duster
1961–1962 Dodge Lancer
1971–1972 Dodge Demon
Chrysler B-Body cars with 41-inch-long torsion bars include:
1962 Dodge Dart
1962–1964 Dodge Polara
1962–1964 Plymouth Fury
1962–1964 Plymouth Savoy
1962–1970 Plymouth Belvedere
1963–1964 Dodge 330
1963–1964 Dodge 440
1965–1974 Plymouth Satellite
1965–1976 Dodge Coronet
1966–1978 Dodge Charger
1967–1971 Plymouth GTX
1968–1975 Plymouth Road Runner
1975–1978 Plymouth Fury
1975–1979 Chrysler Cordoba
1977–1978 Dodge Monaco
1978–1979 Dodge Magnum
1979 Chrysler 300
Chrysler E-Body cars with 41-inch long torsion bars include:
1970–1974 Dodge Challenger
1970–1974 Plymouth Barracuda
The torsion-bar system from a 1972 Dodge Demon consists of two round steel bars (one left and one right) with a 1¼-inch hex on both ends measuring 35.7 inches long. The torsion bars run from the floorpan crossmember to the front lower suspension arms. The rear mount of the torsion bar is inserted into a six-sided socket built into the floorpan crossmember, which is perpendicular to the torsion bar. The front mount of the torsion bar is a six-sided socket built into a lever and attached inside the lower suspension arm, also perpendicular to the torsion bar. The lever in the lower suspension arm has an adjuster that can apply more or less pressure (preload) on the torsion bar.
Torsion bar front suspension systems as used in all Chrysler, Plymouth, and Dodge vehicles (beginning in 1957 and lasting through 1979), are perhaps the easiest suspension systems to modify that were available as original equipment. Torsion-bar front suspensions are very durable and offer easy adjustment of ride height, regardless of age. The torsion-bar suspension system easily converts the front of the car from a streetable setup to a drag-race setup by adjusting or replacing the torsion bars with bars of a different diameter (strength) and adding race-quality single-adjustable or double-adjustable shocks under the front. Once the right torsion bars have been installed, it is very important to have a good set of quality shocks to control the spring rate.
Torsion bars can easily be swapped for bars with a lighter spring rate. Just as you can replace front springs in a GM- or Ford-built car with lighter-rated and taller “trick” springs to create stored energy (allowing the front to raise more readily), you can go to a smaller-diameter torsion bar that produces the same effect. Then the torsion bar can be adjusted with the lower suspension arm adjustment bolt to give the desired ride height, just as you do by using taller or shorter springs with the same weight rating (pounds per inch). Depending upon how you set the adjuster you can add or take away preload, raise or lower the car, and allow more or less weight transfer upon acceleration. Instead of changing to a different spring, the preload is adjusted by forcing rotational twist of the torsion bar. Screwing the bolt in farther puts more pressure (preload) on the torsion bar and unscrewing the bolt applies less pressure (preload) on the torsion bar.
More preload with smaller- diameter torsion bars acts the same as a GM or Ford car with lighter-weight taller springs, which also give the cars stored energy to lift it faster and harder than it previously did. Changing to a torsion bar of lighter weight or smaller diameter requires the adjuster to be screwed in farther, creating even more preload.
Naturally, every car will respond differently. The main idea here is to know that the parts exist and that different shock and torsion bar combinations are available to fine-tune your vehicle’s launch characteristics. Your car’s torque, horsepower, weight, tire size, and gearing has different needs than another similar car with different specifications.
Although many diameter torsion bars are available, the following are recommended as a starting point for maximum weight transfer during hard acceleration.
There is no “one size fits all” setup, nor are there enough pages here to give exact settings for every combination. The following information will help to get you started.
Torsion bars used for drag racing should be of as small a diameter as possible for more weight transfer (pitch rotation), yet strong enough to support the front of the car under all conditions. To plant the rear tires as hard as possible when launching a car with a factory-style suspension, it is necessary to get as much weight transfer (pitch rotation) as possible and to do so as quickly as possible. You don’t want the rear tires to start moving any distance before the weight starts to transfer. Smaller-diameter bars are lighter in strength and weight, and therefore respond quicker than the heavier bars they replace.
For example, 100 pounds taken off a smaller-diameter torsion bar raises the front of the car farther and quicker than 100 pounds taken off a larger-diameter torsion bar. Care must be used when using smaller-diameter torsion bars on the street. Smaller-diameter torsion bars may not be sufficient to control the car in a street-driving situation, even if they achieve what is needed for the drag strip. Traveling down a rough, uneven road surface using smaller-diameter torsion bars can get your car bouncing up and down uncontrollably, like a boat going over rough waves. Be honest with yourself regarding your vehicle’s true intended purpose, and choose the best-possible bar for your application.
Too much weight transfer (pitch rotation) makes the car slower in 60-foot clockings. During pitch rotation, the front bumper of the car rotates in a circle using the rear tires as the axis. Therefore, as the front bumper raises, it is actually moving in an upward and rearward direction. The more pitch rotation and rearward movement of the front of the car, the more torque the engine needs to move the car forward the same distance in the same amount of time.
Although this is also addressed in Chapter 2, it needs to be mentioned here, too. If you are running rear leaf springs that have more arch on the passenger’s side for the purpose of preload (such as the Chrysler Super Stock springs), you need to raise the diver-side front with the torsion bar adjuster to lower the passenger-side rear corner to level the car (side-to-side). This preload on the right rear tire helps control torque roll in the chassis.
The shocks must be upgraded to an adjustable race-designed unit that has the ability to be loosened or tightened as your car demands. Not all tracks are the same, nor is one track the same from week to week. A good set of adjustable racing shocks gives you the ability to adjust your suspension to maximize your car’s performance. Remember, a good-hooking car is more consistent and the driver has a better chance to win the race with the confidence that the car is working right. A good-hooking car with everything else running properly allows confidence and accuracy when predicting ETs.
Many manufacturers offer a good choice of quality adjustable shocks with aluminum bodies for the A-, B-, and E-Body cars. The QA1 PN TC- 1538-P is a single-adjustable shock that I recommend for mild street use and some drag racing with less than 450 hp. The knob has 12 valving options to adjust both compression and rebound (extension) simultaneously, allowing suspension control in one easy-to-reach knob. For drag race only applications with 450 to 600 hp, I suggest the QA1 PN RC- 1538-P, which is similar to the TC- 1538-P except that it comes with a fixed firm compression and 12 valving options to adjust rebound (extension) only. For cars with 600 hp or more, or the racer who wants to be able to fine-tune the suspension for every tenth of a second possible, I suggest the double-adjustable QA1 PN DTC-1538-P. It is adjustable independently in both compression and rebound (extension). This shock has 24 different positions on each knob for a total of 576 valving options. The knobs are clearly labeled. The “+” direction firms the action while the “-” direction softens it.
A good starting point for any adjustable shock is in the middle of the settings. If your car is lifting too high in the front, the front shocks need to be set to a stiffer setting on extension. You may also need to add travel limiters to shorten the travel before the front tires leave the pavement. This greatly reduces the amount of travel before the front tires lift, thus slowing the pitch rotation and making it harder to jerk the front tires as high off the ground. If your car needs more weight transfer, use a looser extension setting and trim (or remove) the upper control arm bump stops for maximum front suspension travel.
If your race car is coming down hard after the launch and bouncing, the front shocks need to be stiffer on compression so the car doesn’t hit the pavement as hard. Ideally the front of your car will come down as softly as it rose. How high your car raises in the front depends not only upon your suspension, but also upon how much torque your combination makes and at what RPM. The proper match of the torque converter (in automatic-transmission-equipped cars), camshaft, and intake within your peak torque RPM range also makes a huge difference in how the car reacts at the starting line upon launch. Obviously, this has a lot more to do with engine design than with suspension, but it does impact how a car launches. A well-matched power package is a big part of finding success at the drag strip.
A lot of drag racing success comes down to power and weight. Finding more power is one thing, but losing weight is another subject altogether. Did you know that cars have two types of weight (sprung and unsprung)? Unsprung weight is any weight below the springs that supports the chassis. Unsprung weight is considered dead weight and cannot be taken advantage of during pitch rotation (weight transfer). The only way to use unsprung weight to your advantage is to reduce it. For example, replacing steel wheels with lighter-weight aluminum versions. Front wheels and tires can also be reduced in diameter and width for greatly reduced unsprung weight. Be sure to check the weight of new wheels and tires before purchasing them. I have seen aluminum wheels that were thicker and actually weighed as much as the steel wheels they were replacing. Rear slicks can be run without tubes to also reduce weight but at a reduction in sidewall stiffness.
In conrast, sprung weight can be used in pitch rotation (weight transfer) to add more weight over the rear axle to plant the rear tires harder. This is where the suspension needs to be fine-tuned to allow the front of the car to go up high enough to transfer the right amount of weight to the rear tires so the car hooks as well as possible.
Another way to take advantage of weight during launch is to remove as much of it as possible from the front of the car. If your car has to run a minimum weight for a particular class, any weight removed from the front of the car needs to be reinstalled in the back of the car. One good example is relocating the battery to the trunk. Safely using the lightest-possible components in the front of the car is always a good way to go to help your car accelerate more quickly. For instance, removing the inner fenders or adding an all-aluminum radiator, aluminum cylinder heads, aluminum intake manifold, fiberglass fenders and a fiberglass hood, all reduce the weight of the front of the car, allowing it to accelerate faster.
Also, lighter-weight front brakes could be used. Chuck Lofgren, Chrysler specialist and owner of Lofgren Auto Specialties, states that on his car, going from factory disc brakes to drum brakes saved close to 20 pounds per side (40 pounds total) in weight. Going to an aftermarket disc brake could save another 15 pounds per side (30 pounds total) in weight. (Lofgren Auto Specialties makes and sells after-market suspension parts and builds engines, specializing in both early- and late-model Chrysler muscle cars.)
Last, but not the least important, are the alignment angles used to correct bump steer or toe change due to front suspension travel. Achieving 1½-degrees positive caster and 1/4-degree positive camber corrects the toe pattern to be within 1/8-inch total toe change throughout the suspension travel.
Torsion-bar-equipped cars are made of a unibody construction, which means they don’t have continuous frame rails from the front of the car to the rear of the car. The frame and body are integrated as a single unit. Structural integrity is designed into the vehicle’s floorpan. For racing, install subframe connectors to tie the front and rear subframes together. This stiffens the car and helps reduce body twist, making the car respond better to racing conditions.
These handy prefabricated connector packages let you tie the front and rear subframe longitudinally and are available for all A-, B-, or E-Body drag cars. Packages include two connectors, brackets, and the necessary mounting hardware. Frame connectors can be bolted in or welded in depending on individual preference. Mancini Racing has more than 45 years of drag racing experience and has developed a line of racing parts for the front or rear of your Chrysler-based race car.
Bars and Cages
Another frame modification you can make is to add a roll bar or roll cage. For bracket racing, current NHRA rules dictate that a roll bar is mandatory in all cars running 11.00 to 11.49 seconds in the quarter-mile (7.00 to 7.35 seconds in the eighth-mile) and all convertibles running 11.00 to 13.49 seconds in the quarter-mile (7.00 to 8.25 seconds in the eighth-mile). But they are permitted in all cars. In my opinion, they are necessary in all unibody cars, not only for safety but for helping eliminate body roll and flex. A well-built roll bar or cage can actually aid traction. Energy that once twisted the body and chassis is now directed to the tires.
Current NHRA rules also dictate that a roll cage is mandatory in all cars running 10.99 seconds or quicker in the quarter-mile (6.99 seconds in the eighth-mile), or any car exceeding 135 mph. For full-bodied cars with unaltered firewalls, floors, and bodies from the firewall rearward with or without wheel tubs running quarter-mile times of 10.00 (eigth-mile 6.40) to 10.99 seconds (eigth-mile 6.99) a roll bar is permitted in place of a roll cage.
The actual rules are more detailed than this, so be sure to consult the current NHRA rule book or call NHRA technical support for the interpretations of the current rules.
Front suspension arm bushings made of rubber were used in passenger cars for both ride and comfort. For racing, they should be replaced with polyurethane bushings for better suspension control. These give the car more stability, and as you make other suspension changes, the car responds better due to the lack of flex in the hard polyurethane as compared with the softer rubber.
Polyurethane bushing packages are available through Mancini Racing, as well as front strut bars to keep the front lower suspension arms in the proper place. Made of heavy-duty steel, these struts are a full 1 inch in diameter, which is 43 percent thicker than the original struts. Also, for those who are weight conscious (remember, lighter means faster), they are available in aluminum which is CNC machined using 7075-T651 material and are .875 inch in diameter (compared with about .700 inch in diameter for the original steel struts). The aluminum weight is 36 percent as much as the equivalent amount of steel, so these struts are both stronger and lighter than the original components.
Mancini Racing carries a complete line of torsion bars and tubular upper front suspension arms. The upper arms are jig built, heliarc welded, and powdercoated. They come with Moog balljoints and urethane inner bushings. Mancini engineers them with some extra positive caster for improved stability. A set of these arms dramatically improves the way your car drives. Mancini also offers stiffeners for your lower control arms with a lower-control-arm plate kit. These kits contain two steel plates and can be welded into any A-, B-, or E-Body lower control arm.
You should now have enough information to get the front of your torsion-bar-equipped car ready for the drag strip. While testing in time trials, focus on the 60-foot times to see if you are making positive or negative adjustments. Remember, one sample 60-foot time is not enough to make any firm conclusions about the next adjustment. A minimum of two 60-foot times must be used. If they are not very similar, you have an issue that needs to be addressed before moving on to another adjustment. Otherwise, you are basing your last adjustment on inaccurate information.
Written by Dick Miller and Posted with Permission of CarTechBooks