Art Morrison Enterprises GT Sport A-Body Chassis - Survival Of The Fittest
The GT Sport A-Body Chassis from Art Morrison Enterprises
From the May, 2011 issue of Chevy High Performance
By Sean Haggai
Photography by Courtesy of the Manufacturer
Through the years, the ’64-72 A-body fameoriginally designed to support passenger car sheetmetal from Chevelles, El Caminos, and wagons has become one of the must-have and best-known platforms around. GM asked nothing more of it than to fetch groceries and haul the family around; it was never meant to handle the serious demands of autocrossing with substantial rubber underneath. It has quickly developed into one of the most popular foundations for performance. While the aftermarket is fat with new bolt-on components for aging A-body frames, Art Morrison Enterprises (AME) has been evolving and looking ahead; completely redesigning GM’s most popular midsize sedan frame from the ground up.
Twisting and flexing are inevitable in high-grip situations, and bolt-on suspension components can only take the factory A-body frame so far before it has reached the limit for structural rigidity and adhesion to the road. It’s not just the additional load created by hard cornering, either. Combine the stresses of a torque-happy mill and the burden the frame is already enduring is intensified. The factory frame was never meant for overexertion, and it’s prone to cracking, thanks to sharp-angle bends and lack of any lateral bracing. To a certain extent, there’s only so much the factory frame can commit to before that resource becomes exhausted and you lose grip.
At the rear, a main crossmember...
At the rear, a main crossmember serves as a location to mount key suspension components like the triangulated four-bar tubes and also as a driveshaft retention device. The wide hoop ties the outer rails together, increasing torsional rigidity but to also allow for a large, custom exhaust to clear the body.
Knowing this, AME went back to the drawing board and reverse-engineered a frame to produce a user-friendly bolt-on chassis in a package that all works like a well-tuned orchestra. Their efforts created the GT Sport frame that’s 600 percent stronger than the original open-channel design by boxing it in and forming a latticework of crossmembers. This created a rigid frame and allowed for additional mounting points for suspension components to work off of. Then AME hung an all-new front suspension utilizing tubular upper and lower arms, and a track-proven triangulated four-bar with a 9-plus housing to complete the rear. To fine-tune the performance level and driving style, adjustable antiroll bars (front and rear) with shocks are available as well. The end result was a new chassis that would be stronger than the original, offer a performance ride and handling, and eliminate the need for serious floor modifications.
Whether you’re looking for an ultralow stance or an all-out autocross warrior, AME’s GT Sport A-body chassis can deliver. It includes some of the best engineering to date, and we were lucky enough to get an in-depth look. We’ve detailed the entire chassis and included everything you’ll need to know, including AME’s line of options for suspension components. Look forward to the GT Sport chassis as early as spring 2011!
Small lateral crossmembers...
Small lateral crossmembers were added to provide extra strength for the center framerails that mount the transmission. They also provide a design feature that permits four additional mounting locations for the underbody ribs to attach on the frame. Joining the body to the chassis in more areas forms a more rigid platform.
Although AME traditionally...
Although AME traditionally makes use of 2x4-inch mandrel-bent rectangular tubing for framing, this boxed rail was designed to maximize chassis stiffness while maintaining a low profile. The extensive use of FEA (finite element analysis) programming designed a rail that’s more rigid than the OE piece but still fits the stock floorpan. The boxed rail design also minimizes the amount the rail hangs below the pinch weld, creating an aesthetically clean look for the finished car.
GT Sport motor mounts are...
GT Sport motor mounts are an integral part of the chassis structure. They are designed from thick, 1.5x0.120-inch mandrel-bent tube and also work as gussets to increase rigidity to the front crossmember. The mounts will cradle small- or big-block power, although AME has also created a bolt-on adapter plate to mount the extremely popular LS engine platform.
Extending chassis utility...
Extending chassis utility and strength within the chassis, AME’s transmission crossmember is designed to mount virtually any transmission. The built-in adjustability allows nearly any transmission fitment from a Powerglide, to a 4L80E, or a T56 six-speed. AME also designed exhaust notches to maximize room and tuck the exhaust closer to the frame.
The front portion received...
The front portion received an all-new suspension design with a new crossmember and steering arm to support aggressive handling and capitalize on the use of extra-wide rubber. AME went through nine alterations before finding a package that placed the suspension correctly around the engine and pulleys. It’s based on the C6 Corvette upright and includes a new set of tubular control arms with 4.5 degrees of caster and static 0.5-3 degrees of negative camber gain. Uprights also allow for numerous brake options.
Upper A-arm pivots were fabricated...
Upper A-arm pivots were fabricated using AME’s in-house CNC machine. The pivots are designed with strength and adjustability in mind and housed in polyurethane bushings to provide driver comfort with Zerk fittings for grease. Adding or removing spacers behind the pivots allows fine-tuning of the geometry.
Having the ability to modify...
Having the ability to modify the suspension gives the end user a greater range of adjustability. AME is now including tubular adjustable antisway bars on all its frames, including the GT Sport A-body chassis. The A-bodies will receive a 11/8-inch hollow bar up front with a 3/4-inch solid bar out back. With three adjustment holes, it’s easy to make significant changes to the roll stiffness.
While welds are visually pleasing...
While welds are visually pleasing to the eye, they also serve to strengthen joints. All Art Morrison chassis welds are completely done by hand with a MIG, while the suspension components, like the control arms, are all TIG-welded. This is done to maintain control and accuracy throughout the build process.
As part of the suspension...
As part of the suspension packaging challenge for the front suspension, mounting the rack-and-pinion while allowing enough room for the engine was a challenge. AME’s rack-and-pinion for the GT Sport will clear any powerplant and uses a shorter steering arm with a 20:1 ratio. This gives the chassis a neutral feel through the steering without eliminating any feedback from the road.
Basing the rear around the...
Basing the rear around the Currie 9-plus center, AME welds on its own axletubes, brackets, and CNC housing ends in-house. It’s a tried-and-true triangulated four-bar rear suspension adaptation of the original suspension, although the upper and lower arms are tubular. By altering the geometry, the result is a stable suspension with a solid roll center that can take corners with ease.
Keeping with the adjustable...
Keeping with the adjustable nature of the suspension, the GT Sport A-body chassis features adjustable Strange Engineering coilover shocks as a standard feature. The single-adjustable shock allows the customer to easily fine-tune their ride with a simple click of the shock’s dial. For all-out performance, AME also offers double-adjustable strange shocks as well as the full range of Penske Racing Shocks.
A positive side effect of...
A positive side effect of the GT Sport frame’s unique design is that it opens up a ton of space in the front and rear, allowing the ability to run a variety of tire sizes. Race-wide tires are no problem; the front will support a maximum P275 tire and the rear will suck up a massive P335 with no clearance issues on the frame. CHP