Words: Tommy Parry
Coming off the back of their success with the HellBoy C10 and Velocity Camaro, Keith and Bob decided to push the envelope and progress past where the two aforementioned builds were limited – all while sticking with the rules of SCCA and hillclimbing. They started with the vision of pushing a Trans Am well past the conventional goalposts, and expanded the idea of what a Pro Touring machine could be.
The appeal of the TA is obvious. Great lines, a modest wheelbase, a curb weight just under 1.5 tons and one of the slipperiest cars to come out of the states in the 1980s, it holds plenty of potential.
However, as the car was pushing 30 years, they opted for a full tube frame. The advantages in strength, safety and weight are undeniable. It also dovetailed nicely into their considerations about geometry and suspension adjustment.
Having a widely adjustable suspension that is both accessible and quickly adjusted, as time between run sessions are usually brief, was the next aim. Front alignment (caster, camber, toe, roll center), rear alignment (camber, toe, roll center, roll steer), shock valving, shock rubbers, spring load, spring rate, sway bar rate, gear ratio and brake bias were all taken into account.
They also wanted to keep the majority of mass low and as near to the center of the car as possible. They began by moving the engine further back by a few feet, and a few inches lower, thanks in part to a thin A&E oil pan for the dry-sumped setup.
To relocate the engine, they grabbed a big chunk of aluminum and whittled out a bearing plate. It bolted to the bellhousing and carried an input bearing from a super T-10 (in a wet oil cavity), and also had bolt-up provisions for a TH-400 tail shaft. All that was needed then was a custom shaft that fits a 26-spline LS to a TH400 slip yoke.
For ideal weight distribution, they started searching for a transaxle that would plant the rear tires, trim some weight from the car, be easily serviced with available parts and not break their conservative budget. They decided on a Speedway Engineering Quickchange IRS center section with a Platinum-Drive diff unit. This was built to accept Porsche style 934 CV joints with 33 spline axles, and allowed the team to raise the diff to an 11.800″ centerline. This kept the axle/CV angles within range at full stroke of the suspension, cemented the driveline direction and allowed them to move forward into full fab stage.
Careful consideration of the suspension geometry came next. With ball joints and tie rod ends on the rear knuckles, they were able to make rear toe adjustments quickly, accurately and easily. This style of modification also allows them to tune the roll-steer of the car, as well as set a baseline toe-in on the rear.
Next came the exhaust. Their plan was to route the exhaust (heat) out and under the rockers, then in and under the differential and out the back of the car. The OE rocker is plastic, so they made some aluminum rocker skirts to prevent a fire. With just enough room to fit a 2 1/4″ x 4″ oval tube under the rocker and the bottom flat and flush with the bottom of the chassis, they were truly threading needles with this compact, crowded layout.
The header flanges are 3/8″ thick – a little heavy, but they shouldn’t leak. Just one of the many compromises made in the name of reliability which, for a car that is intended to see plenty of track time, takes precedence over overall weight. The primary tubes start 1 3/4″ and then step to 1 7/8″, and are a little shorter than desired at approximately 17″. This hinders the torque curve somewhat, but the improvement in heat management is worth it. Just another item on the long list of this car’s sensible compromises.
After deliberating over a Wilwood firewall-mount pedal set, they realized it was too much of a compromise. The ratio was not exactly what they wanted, the pedals didn’t fit as nicely as they would’ve liked, and getting to the masters would be outside of their maintenance window. So, they custom-fabbed their own. Again, a racing car must be serviceable and provide a strong interface with the driver.
Additionally, some keen eyes may have noticed the manual rack. Being sick and tired of pumps, pulleys, belts, hoses, coolers, heat and leaks, they avoided conventional power steering.
The Trans Am has come a long way since Keith and Rob started on it, and it’s only continuing to grow towards what might be the ultimate Pro Touring Pontiac. Give it time — with their technical understanding, ability to weigh pros and cons and single-minded focus on usable performance, these two have all it takes to make something truly special.
For more on this machine and a better understanding of the complicated considerations made when building a purpose-built racing car, you can follow their build thread here.
