Adding Rigidity To An F-Body With BMR Suspension

The GM F-body was first released back in 1967 with the introduction of the Chevrolet’s Camaro and Pontiac’s Firebird. These cars were a very versatile platform and could be found on drag strips and road courses too.  And while they were great for racing, some areas needed to be beefed up in order to be really competitive. Unlike other cars, the F-body utilized a unibody design, meaning they never had a full-frame under them. The problem with the lightweight unibody design is they have a tendency to flex when additional power is added. 

Over the years, GM kept the same unibody design in the F-body, but ditched the leaf spring suspension and subframe that was available from 1967-’81 on both the Camaros and Firebirds. In 1982 these cars received a torque arm rear suspension, strut front suspension, and a K-member with struts instead of the traditional coil springs and subframe. While the third- and fourth-gen body and suspension is a bold improvement over the older design, it still has its share of problems that need some attention if you want them to rip on and off the racetrack.

Flex Is Bad

One of the biggest problems with an F-body is flex. We talked to Jonathan Cutler, Marketing Director of BMR Suspension, about F-body flex, and he said, ” A unibody does not handle twisting forces as well as body on frame designs.” 

Since these cars don’t have a frame, the bodies can bend and twist under the additional load when you add larger tires and more power. But flex is not associated with just the car’s body. These vehicles also suffer due to weak stamped steel suspension components. By eliminating the vehicle’s flex in the body and suspension, they become more efficient, putting what would be wasted energy into the ground. This change in dynamics offers better 60-foot times and straighter launches at the dragstrip, and quicker autocross times.  

In our first article, we installed a set of BILSTEIN shocks, BMR springs, sway bars, and lower control arm relocation brackets, which are shown in the top portion of this image. In this installment, we will focus on the BMR components in the lower part of the picture to stiffen up our WS6.

So what BMR suspension parts do we need to add to reduce the flex problem with our WS6? 

“Subframe connectors are a must for the body as they will join the front and rear subframe together making the chassis more rigid,” explained Cutler. “For the suspension, lower control arms (LCAs) and relocation brackets will make the most notable improvement in traction. And, replacing the factory stamped steel torque arm will reduce deflection and allow you to apply more power to the ground.”

Subframe Connectors

Our first step to reduce the chassis flex on our WS6 was to add a set of BMR Suspension’s subframe connectors (PN SFC023). This product offers a two-point bolt-on design that dramatically reduces chassis flex while increasing performance by tying together the car’s front and rear. They are manufactured from 2 x 2-inch heavy-duty steel tubing and laser-cut 3/16-inch steel plate, CNC-formed and available in red or Hammertone black. 

BMR’s subframe connectors tie the front and rear of the car together, adding rigidity to the structure of the vehicle.

The installation of BMR’s subframe connectors is straightforward, thanks to their design. The process can be done in a garage with jack stands and hand tools in just an hour or two. 

BMR's subframe connectors are very well engineered and their bolt-in design makes for a quick and easy installation. They also tuck up nice and tight under the body of the car giving you ample clearance.

With the car securely placed on jack stands, we removed the rear control arm front bolt on the driver’s side. We then used the supplied insert and slid it into the Firebird’s body. Next, we lifted the frame connector into place and used the provided hardware to secure the unit. We then moved over to the passenger side and repeated this process.

Tubular Lower Control Arms

The stamped steel lower control arms on the rear of an F-body leave a lot to be desired. They flex when cornering, causing erratic handling characteristics. They also utilize soft rubber bushings, which causes deflection leading to a host of other problems like wheel hop. BMR’s lower control arms (PN MTCA001) address these issues, allowing the F-body to launch harder while adding consistency to the vehicle in a straight line and in and out of the corners.

The factory rear control arms flex under a load causing erratic handling. They also utilize soft rubber bushings, which causes deflection leading to a host of other problems like wheel hop. BMR’s units cure all of these problems with a tubular design and polyurethane bushings.

The BMR’s lower control arms are manufactured from lightweight 1.625-inch 4130 chrome-moly tubing and include polyurethane bushings. The 95-durometer bushings are greaseable and internally fluted, perfect for high loads, and offers quiet, reliable operation. 

Like the subframe connectors, installation is a breeze. We started with the driver’s side and removed the front and rear bolts to remove the OEM lower control arm. We then replaced it with the BMR unit before reinstating the hardware. With the driver’s side complete, we moved on to the passenger’s side. At this point, we went ahead and torqued down the subframe connectors and the rear control arms to BMR’s specifications. 

BMR’s subframe connectors tie the front of the car to the lower control arm mounting point which helps to eliminate flex in our WS6.

Torque Arm

The torque arm on the F-body ties the rear axle to the transmission. This design has proven to be quite capable with drag and road racing. But, as you probably guessed, flex is a problem. Much like the rear lower control arms, this OEM part is stamped steel and uses a rubber bushing setting up a recipe for problems when power and traction are added. BMR’s torque arm (PN MTA001) is specifically designed with street performance, drag racing, and handling in mind. This unit is made of chrome-moly and is significantly stronger than the OEM part. It eliminates deflection allowing more power to hit the tires without a massive increase of noise and vibration thanks to the 95-durometer polyurethane bushing. BMR’s torque arm is also adjustable, allowing the user to dial in the rear axle’s pinion angle. 

As they say, ” A picture is worth a thousand words.” You can certainly see the differences between the adjustable BMR torque arm and the OEM. The BMR unit is made of chrome-moly and is significantly stronger than the factory part. It eliminates deflection allowing more power to hit the tires without a massive increase of noise and vibration.

The installation of the torque arm is not hard, but is somewhat involved. We started with the vehicle supported by jack stands under the frame to allow the rear axle to fall to its furthest point. With the rear end supported by a jack, we unbolted the shocks before lowering as far down as possible. We then removed the two large bolts from the rear of the torque arm and then the front torque arm mount from the T56. This mount is a clamshell design that will need to be modified to accept the new bushing. We located the four rivets, as stated in the instructions, before drilling them out. This allowed us to remove the factory rubber mount and made room for the BMR bushing. We then bolted the mount to the transmission before slipping the bushing onto the torque arm. With the bushing on the end of the torque arm, we installed the clamshell side of the bracket and reinstalled the hardware. 

We had to modify the factory torque arm bushing mount to accept the new BMR polyurethane bushing. This process is easy and can be done in any garage in just a few minutes with a centerpunch and a drill.

Unfortunately, we were not able to set the pinion angle at this time because we couldn’t find our magnetic pinion tool, which BMR offers (PN AF001). If you don’t have one, or if you can’t locate it, pick one up before starting the installation. It will allow you to set the pinion angle by measuring the driveshaft’s angle and the rear axle. To make adjustments, simply turn the adjuster on the torque arm. For an automatic transmission BMR recommends 1-2 degrees negative, and 2-3 degrees for a manual. 

The BMR torque arm is adjustable, making it easy to set the pinion angle for optimum traction.

Strut Brace

Our final piece to limit the flex on our WS6 was BMR’s strut tower brace. Like the subframe connectors, this part is not original equipment on the 1993-2002 F-bodies. However, it certainly adds more rigidity between the two strut towers thanks to its design and chrome-moly structure. 

The last piece of the puzzle was BMR's strut tower brace. This product eliminates any flex between the two strut towers.

To install BMR’s strut tower brace, we removed the front two nuts on the struts from both the driver’s and passenger’s side. Then we slid the strut bar on the nuts and reinstalled the nuts. Depending on the car model, you might need to push over the brake line or remove an A/C line support tab, both of which are easy modifications. 

With our WS6 stiffened up, we’re one step closer to hitting the race track. Since we have eliminated the Firebird’s flex, we won’t have to worry about wheel hop and will be able to put all of the power to the ground. The only problem now is we need more power and larger tires of course. 

 

Article Sources

About the author

Brian Havins

A gearhead for life, Brian is obsessed with all things fast. Banging gears, turning wrenches, and praying while spraying are just a few of his favorite things.
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