C1 Corvette Sport Chassis - Frame Job
Deconstructing Art Morrison's Criminally Cool GT Sport C1 Chassis
Writer: Bill Holland
photographer: Tom Owen, Craig Morrison
As best we can tell, C1 Corvette owners can be divided into three different categories. Those in the first group prefer to keep everything absolutely original. To them, any variation from stock is something akin to heresy. Category number two's members are a bit more open-minded, going so far as to make subtle changes to enhance their vintage Vettes. Finally, there are those radical few who are willing to do whatever it takes to improve the performance of their rides. For them, noted chassis builder Art Morrison has developed the C1 GT Sport chassis.
Although Art Morrison Enterprises has been cranking out a variety of top-quality frames for more than 30 years, it wasn't until the Fife, Washington-based firm introduced its bolt-in GT Sport chassis for '55 to '57 Chevys that it hit its first home run. Thanks to a sophisticated independent front suspension and triangulated four-link in the rear, the chassis gave "shoebox" Chevy owners a vehicle with sports car handling and a superb ride.
The new Morrison GT Sport Corvette chassis offers even more stunning performance, providing contemporary suspension technology to replace the over-50-year-old C1 frame. It will also make an excellent platform for a ground-up "kit car" using one of the several available fibreglass C1 replica bodies. Talk about a pedigree. When word of the new chassis came out, noted hot-rodders such as Boyd Coddington and Chip Foose were among the first in line. Coddington's '54 Vette project was even featured on the car builder's popular SPEED TV show, American Hot Rod.
The Hardware
What makes the GT Sport chassis tick? For starters, it employs a C5 Corvette front suspension, with forged aluminium control arms and fully adjustable Strange Engineering coil over shocks. But there's more to it than simply slapping some trick A-arms in place. The entire chassis has been computer-engineered for optimum handling and zero bump steer, so it can corner with the precision of a slot car. Because the body of the C1 is narrower than that of later-model Vettes, the track width has been narrowed, and AME's engineering department slightly increased the scrub radius for better driver feedback. With 9-inch-wide front wheels and 6.5-inch backspacing employed, everything is contained within the stock wheel wells. The front-view swing-arm arc has been shortened to maintain better camber angle during cornering, while the static roll-centre height has been reduced to minimize side scrub and jacking force. As a result, straight-line stability and ride quality have been enhanced.
The rear-end features a triangulated four-link suspension. This is a "best of both worlds" situation in which the upper, angled bars provide lateral stability while the lower bars control housing "wrap" under hard acceleration. And if you're wondering why a C5 IRS is not employed, it's because the C5's track is too wide to fit under the C1 body. The C5 setup is also quite costly.
Steering is handled through an AGR power rack. This hydraulically augmented system is offered in 15:1 and 20:1 ratios-which equate to 2.5 or 4 turns lock-to-lock, respectively. The former is best suited to aggressive driving on winding roads, while the latter is ideal for highway cruising.
Excellent braking is achieved through use of the 13-inch front discs from the C5 and an SVO rear-disc kit. For even more braking power, Wilwood six-piston callipers and 14-inch rotors are available optionally.
The frame itself is made from mandrel-bent 2-by-4-inch rectangular tubing, which is fixture-welded by AME's experienced craftsmen. To ensure perfect alignment, the core support and suspension, body, engine, and transmission mounts are installed while the frame is in the jig.
Among the most important features of the AME GT Sport chassis are the in-frame passages that allow the exhaust system to be routed through the frame rails. This allows for a lower-than-stock centre of gravity while also maintaining ample ground clearance.
A wide variety of drive train combinations can be employed, as there are motor mounts available for both the traditional small-block Chevy and the newer LS-series power plants. Most manual and automatic transmissions will also fit.
The Installation
What's involved in retrofitting a C1 Corvette with a Morrison GT Sport chassis? The operation is actually straightforward and can be accomplished by a competent do-it-yourselfer with access to a well-equipped garage.
To start the process, it's necessary to disconnect any items that would prevent the body from being lifted off the chassis, such as steering, pedal linkages, brake lines, and so on. Then it's simply a matter of unbolting the OEM Corvette body and core support and plucking the body off the frame. Morrison recommends using a two-post lift, with the arms positioned just in front of the door opening and forward of the rear wheel well. The body will lift off in one piece.
After the body is removed, some minor alterations will be required prior to re-installation. First, the inner-fender panels will need to be trimmed slightly to clear the C5 suspension. Next is the issue of the transmission tunnel. Most aftermarket trannies will clear, with the exception of the T56 six-speed. This trans is fairly wide in the back, and the tunnel must be expanded accordingly.
C1 Corvette Sport Chassis - Frame Job
The wheel/tire package is the next item to address. As you know, the first-generation Corvette came with tall, skinny rubber. Well, you're going to have to kiss those OEM 15-inchers goodbye, because the smallest rim that will fit over the C5 front brakes is a 17-incher. And since most-if not all-modern performance tires are significantly wider than their '50s and '60s counterparts, the rear wheel wells will almost certainly need to be widened for clearance. On Art Morrison's '60 Corvette, 265s on 9x18-inch rims were used in front, and 295s on 10x18-inch rims were employed in the back. Although this configuration required that the rear be "tubbed" by about two inches, it provides an excellent contact patch and should be capable of near-1g turns.
As you can see from the accompanying pictures, the body mods are relatively minor and do not adversely affect the appearance of the car. The GT Sport chassis even incorporates spare-tire and license-plate mounts in the stock locations.
If you want to keep the factory steering column, you'll need to shorten it at a point approximately seven inches out of the firewall, with about 1 1/4 inch of the shaft hanging out. You'll also need to mill a flat on the shaft, corresponding to a "double D" U-joint and requisite stub shaft. This will be used to connect the steering to the AGR rack that comes with the chassis. If you don't have access to a mill, an aftermarket replacement column will work.
The OEM radiator will bolt to the core support of the Morrison GT Sport frame. However, employing the factory shroud is somewhat risky, as its fit is fairly loose and open. Morrison used a PRC aluminium radiator and Flex-A-Lite electric fan on his own C1, and then fabricated a custom shroud to provide a tight seal.
As we mentioned earlier, the Morrison chassis is set up to accommodate both late-model LS and original SBC power plants, with motor mounts and special headers available to fit either. The GT Sport's through-frame exhaust passages even make it possible to install mufflers in the factory location, providing for the use of factory-style through-bumper exhaust tips.
Morrison offers the setup in three basic configurations. There's a complete bare chassis with less suspension; a "chassis with suspension" that includes C5 control arms, a power rack and pinion, front and rear adjustable coil-overs, a nine-inch housing, and a triangulated four-link; and finally, a complete chassis that's got everything needed for a "roller" except tires and wheels.
As you can see, the Morrison GT Sport chassis gives C1 owners and custom car builders the ability to combine the classic styling of early Corvettes with the performance and handling of their newer siblings. It's the proverbial "marriage made in heaven"-and an outstanding investment in long-term driving pleasure.
Morrison is shown pre-fitting the rear-suspension components. The chassis' triangulated four-link setup provides excellent lateral control and harnesses housing "wrap" under hard acceleration.
C1 Corvette Sport Chassis - Frame Job
The rear sway bar anchors to the frame via rugged polyurethane bushings and a control rod. /
A key attribute of the GT Sport chassis is the manner in which the exhaust is routed through the frame. This allows the car to be built with a low centre of gravity without sacrificing ground clearance. /
Looking down over the rear housing, the unique manner in which the coil over shock is mounted and braced is quite evident. This configuration has proved to be very reliable, according to Morrison.
This back-to-front shot shows the transmission and exhaust system being positioned. The two dished cross members aft of the tranny serve to stiffen the chassis and prevent any driveshaft mishaps. /
Mufflers can be nestled in the OEM location, allowing for factory-style through-the-bumper exhaust outlets. Also shown is the beefy nine-inch Ford rear, which can handle any amount of horsepower and has the industry's widest selection of ring-and-pinion-gear ratios. /
Triangulated four-links are equipped with Morrison's special polyurethane-bushed stainless steel rod ends. They provide an excellent combination of firm ride control and quiet operation for street use.
Another innovative feature is this "stepped" trans-mount setup, which can accommodate most popular manual and automatic trannies simply by swapping cross members. /
The use of an LS-type power plant is made possible with special motor mounts and these custom-made headers. They're specifically designed for use with a through-frame exhaust system. /
This shot of Morrison next to his under-construction '60 provides visual proof of just how low a C1 can go when fitted with a GT Sport