Modified Fun - written in mid ‘82.


Gale Banks Trans Am Firebird

- Even the best of us occasionally drift beyond the limits of driving prudence. The temptation to do so is particularly strong at the thermonuclear end of the potency scale. Our top-speed testing of Gale Banks's twin-turbocharged Pontiac Firebird Trans Am is a case in point.

This car has but a short, 3.42:1 rear axle ratio to harness its 560 horsepower, so we knew our top-speed testing would be just a simple hinge up to the 7000-rpm redline. With this in mind, we selected one of our shorter, but more convenient, California test sites instead of a more suitable, but distant desert venue, After waitmg for the mld-afternoon traffic to clear, with Gale Banks as my observer, I put the blown Trans Am's pedal to the floor Sure enough, it attained its 156-mph maximum in barely more than a mile, at which point we were rapidly closing on several cars that, had been mere flyspecks when we started the run.

I applied the brakes hard but without serious concern, since there seemed to be plenty of room to slow down before we would be into the traffic. Unfortunately, the Trans Am's brakes absorbed only about 50 mph of our speed before fading into futility. By then we were virtually on top of the traffic, which had artfully arrayed itself to block both lanes of the freeway. We took the left shoulder (an exit ramp clogged with more slow-moving traffic occupied the right), since. it was the only uncontested pavement remaining. But this was only a brief respite, since the shoulder ended abruptly as the road funneled into an overpass. Fortunately, since we were still at a three-digit speed, we were quickly past the blockers and back on the road with room to spare.

This top-speed exercise turned into more of an adrenalin high than usual, but the Trans Am's engine can duplicate the rush at practically any speed, Acceleration from rest was leisurely because of a poorly matched torque converter, but once we were rolling, 60 mph flashed by in 5.2 seconds. When the engine finally reached boost, the more serious accumulation of velocity began. In a mere 4.7 seconds more, 100 mph was attained, and 130 mph took only an additional 6.1 seconds. In the process the quarter-mile was covered in 12.9 seconds at1l9 mph.

To put this performance in to perspective, the sixteen-second 0-to-130mph time is over ten seconds quicker than a BMW M1’s and the 100-to-130 mph time of 6.1. seconds is less than a Porsche 911 SC needs to accelerate from 60 to 90 mph. The Trans Am's rocket sled acceleration never seems to stop.

The motivation for this is the Gale Banks twin-turbo, 560 bhp engine. Although Mr. Banks has been in the turbocharging business for thirteen years (in San Gabriel, California), he's better known for his marine engines than for his automotive work. The engine in the Trans Am uses much of his race-boat technology redirected toward. automotive application. It's based on the 350 cubic-inch Chevrolet V-8 with all of the heavy-duty factory parts: a beefy marine block, a forged-steel crankshaft, forged connecting rods, and large valve cylinder heads. Banks starts with basic blueprinting and balancing, then adds his own forged pistons with an 8.4: 1 compression ratio, a turbo camshaft, an Edelbrock Torker intake manifold, a modified Holley four-barrel carburetor, a special ignition system and, most important, the turbocharger components.

The heart of the system is two Rajay 301 E turbochargers, which are mounted on exhaust manifolds welded from tube forgings and feed a cast-aluminum chamber above the carburetor. Two Boost-Guard waste gates limit the pressure to 12 psi, while another valve in the carburetor chamber blows off excess pressure when the throttle is closed to help maintain turbo speed. An external metering circuit adds fuel to all four carburetor throats when activated by a pressure switch during high-boost conditions. For additional detonation control above 6 psi, water is injected into each compressor inlet by boost pressure. The turbos exhaust through two low-restriction mufflers via 2.5-inch-diameter pipes. All of the componentry is top-quality and beautifully finished.

Despite all of the hard-core performance parts and massive power output, the engine is amazingly docile. It idles smoothly and evenly at about 750 rpm,\ and is responsive and tractable, even at low rpm. The low-speed drivability is appreciated since the turbos don't really spin into action until well above 3000 rpm. This is indicative of Banks's marine background: high-rpm-only boost is typical of turbo boat engines, which are required to develop serious power only in the upper half of the rpm range. The automatic transmission fitted to the car is another stumbling block, for it resists demand downshifts and is linked to the engine through an overly tight torque converter.

This problem is not debilitating in the Banks car, however, because the engine makes 270 horsepower unboosted, or 100 more than the healthiest stock Trans Am powerplant. When the boost arrives it comes in quickly but without the kind of violent snap that can usurp driver control.

The Trans Am received minimal modifications to accommodate its additional 400 hp. Goodyear Eagle NCT tires (P245/60R-15) mounted on 7.5inch-wide Center Line Champ 500 wheels were fitted for enhanced high-speed durability. All rubber was removed from the rear axle's locating linkage. Recaro seats were fitted for maximum passenger support, and a l50-mph speedometer was installed to match the car's true capabilities. With these changes the Trans Am felt very stable and solid at speed, and was quite at home with its newfound muscles. It had more than enough go to match its swoopy looks.

The entire project was so successful that we're planning to work with Mr. Banks and certain other automotive maestros to build an even better version of the Trans Am-one with similar power spread over a broader rpm range, plus upgraded suspension, BIG brakes, and a five-speed manual transmission (to optimize overall gearing). With these changes the top speed will no longer be rpm-limited; it promises to be much higher. And we promise we'll make the trip to the desert to find its true potential.

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Second Try

Author: ArchitectPage

body style not tested car