Last month, Department X focused on a very unique V-6-powered Trans Am built and tested by Pontiac Special Vehicle Engineering. It was proposed as a possible alternative for a high-performance engine option if the large-displacement V-8 engines were to disappear from the lineup. The experiment was a success, as the supercharged 3800 V-6 proved to have at least as much power as the LT1 V-8s in production at the time.
This month, we are featuring another experimental Firebird, actually a sister car, built around the same time at Pontiac SVE. Like the black Trans Am, this red, steel-roofed Formula was an early '93 model upgraded to WS6 specs, featuring a smaller-displacement, supercharged engine. This time however, a V-8 was used. It also ran as if there were a much larger engine under the hood.
As mentioned last month, there was some question at the time as to whether large engines would have a place in anything other than trucks. Talk of tightening legislation, in the form of tougher CAFE standards and other directives, sent Pontiac back to the drawing boards to seek alternatives should those scenarios actually play out.
The supercharger used on the 4.3L engine was an experimental Eaton unit with a top-side air inlet. It displaced 112 ci per revolution and was larger than either of the units used on the production 3800 V-6 engines. Note the orientation of the throttle body to the blower. A large pulley kept boost down to 8.5 psi.
Pontiac had been using forced induction for more than a decade. They learned the advantages of making small engines run like big ones, while maintaining frugal mileage and light weight. The '80-'81 Turbo Trans Ams, the Sunbird Turbos of the '80s, the '89 Indy Pace Car Trans Ams, and more recently, the SSEi supercharged V-6 Bonnevilles showed that performance was indeed possible using smaller engines.
For this particular exercise, the engine used was the 4.3L, 265ci L99 V-8. It had seen duty as the base engine in the Chevrolet Caprice, which had ceased production in 1996. Externally identical to the LT1 used in the Firebird Formula and Trans Am, it used a 3.75-inch bore and a 3-inch stroke, just like the '55-'56 265 Chevy V-8.
In its stock form, the L99 was rated at 200 hp at 5,000 rpm and 240 lb-ft of torque at 2,400 rpm-not bad, but not that great either. If the performance reputation of the Firebird was going to be upheld, there was some work to be done on the mini LT1, and that is just what happened. Pontiac SVE beefed up the little V-8 considerably, adding a set of ported 350 LT1 heads with 1.94-inch intake and 1.50-inch exhaust valves, which were actuated by a stock LT1 camshaft.
Then things got interesting. The stock L99 induction system was removed and replaced with a custom intake manifold that mounted an experimental Eaton 112ci Roots-style supercharger and a one-off air-to-liquid intercooler. The blower was driven at a 1.93:1 ratio and maximum boost was set at 8.5 psi.
Aluminum ducting routed air from the throttle body, under the windshield, and into the blower.
Due to the blower's top-facing inlet, the air made a rather unusual journey to the combustion chambers. From the Ram Air hood, air entered a non-production airbox, which ducted it to the throttle body on the driver side. The dual 58mm LT1 throttle body was mounted on an elbow like the black V-6 car, but the assembly was located on the driver side. From there, custom-fabricated aluminum ducting routed behind the blower and then up into the Eaton's air inlet.
Once compressed, excess heat was picked up by the intercooler's finned element, which was mounted inside the intake manifold. Then the compressed and cooled air entered the cylinder at more than 1.5 times atmospheric pressure. After the combustion event, the spent gasses passed through factory LT1 manifolds to a prototype single-exhaust system, a later version of which ended up on the '98 WS6 Formulas and Trans Ams. Though it was a single-outlet system, it actually flowed substantially better than the duals used on non-WS6 V-8 Firebirds.