Pontiac Grand Prix 300 GPX

Article by Charles Ross
Photography by Scott Killen
Motor Trend Copyrights, March 1995
HTML coding and scanning by Paul Mercier

Power makes a musclecar, and the greater the power, the greater the musclecar. By that standard, the Pontiac 300 GPX lays claim to the division's musclecar heritage more rightfully than any Pontiac since the '70 GTO Judge. Three hundred horsepower from a supercharged version of GM's supple Series II 3800 V-6 lets this sneak-preview of what will likely be the next Grand Prix claim just about anything it wants - and lay waste to many preconceived notions of what a great musclecar is or can be. Although Pontiac is showing the 300 GPX as a "concept car", it's much more "car" than "concept". Rumors from Pontiac indicate that, except for the exaggerated wheel arch flares, this is very close to what the 1997 Grand Prix will be - including the powerful V-6. And we tested it.

For 1996, Pontiac is readying the supercharged 3800 Series II 3.8-liter V-6, an upgunned version of the engine currently used in the Bonneville. The concept tester is pressurized to 10 psi and makes 300 horsepower via functional Ram Air hood intakes and an air-to-water intercooler.

While the rest of the car is intriguing, it's the engine that's truly inspiring. The 90-degree, pushrod, two-valve-per-cylinder, 3.8-liter V-6 is equipped with a Roots-type twin-lobe Eaton Model 90 supercharger capable of forcing 550 cubic feet of air per minute into the engine, and producing a maximum boost pressure of 8 psi. Reclaiming Pontiac's historic Ram Air induction system, the 300 GPX twin hood inlets duct outside air to the supercharger's air-to-water intercooler. The result is 300 horsepower at 5500 rpm-75 more than the supercharged Series I 3800 currently available in the Bonneville SSEI and 95 beyond the output of the normally aspirated Series II standard in base Bonnies.

It's not the horsepower figure, however, that tells the supercharged tale of the GPX engine; it's the amazing torque production. Using the Eaton supercharger's instant boost characteristics to brilliant effect, the GPX bursts with 335 pound-feet of torque at only 3500 rpm (compared with the normally aspirated engine's torque peak of 230 pound-feet at 4000 rpm). That's 10 pound- feet more peak torque than the 5.7-liter LT1 V-8 in the '95 Trans Am. Recalling MotorTrend's test of the original '64 GTO, that car's 389-cubic-inch (6.4-liter) four-barrel V-8 spat out a rated 428 pound-feet of torque at only 3200 rpm. But if you keep in mind the wild optimism of that era's often-spurious "gross" engine rating methods, the GPX's net-rated torque production looks just about even with that of the old classic musclecar. Quite an accomplishment for an engine with two fewer cylinders and 2.7 liters less displacement. The supercharged Series II 3800 with an output of 250 horsepower will go into production for the '96 model year. If and when the GPX hits the assembly lines the year after that, power is expected to be closer to the 250 than the concept car's 300.

Unlike the original musclecars, the GPX is a thoroughly modern front-driver with its engine mounted transversely. The transmission is a carryover 4T60-E four-speed automatic unit from the '95 Grand Prix helped by the remarkable Torsen Traction System. The Torsen scheme is a clutch-free traction-control system. Torsen's unique no-slip gearing system governs torque transmission, torque proportioning, and differentiation in a single unit.

Styling-wise, the current Grand Prix was blended with today's Grand Am and shaken with future-think; out poured the GPX concept car. Rumors have the '97 Grand Prix looking similar to this version, with base and performance models featuring different faces; air intakes will likely reside below the bumper fascia for performance models, above for base cars.

While based upon the current GM-10 platform, which forms the basic structure of the Buick Regal, Oldsmobile Cutlass Supreme, Chevrolet Lumina, and Monte Carlo, as well as the current Grand Prix, the GPX represents a significant update. Using the new rear suspension that first appeared on the '95 Lumina and Monte Carlo, the GPX loses the current Grand Prix's transverse composite leaf spring in favor of coil-sprang struts with three locating links per side. The front suspension remains MacPherson strut-based and receives steering input from the same high-tech magnetic variable-speed assisted rack-and-pinion unit GM uses in the Oldsmobile Aurora and Buick Riviera. Thick anti-roll bars and gas-pressurized shocks help with handling, though the track on the GPX is exaggerated by its Mississippi-wide P255/40ZR18 tires. In fact, the front track is increased 5.5 inches over that of the '95 Grand Prix, while the rear is spread apart an additional 7.25 inches.

With the update of their rear suspension designs, the Lumina and Monte Carlo lost their rear disc brakes. The GPX, however, has kept all four discs, with big 11.9-inch rotors in front and 11.5 inchers at the rear. For economy's sake, at least on the base Grand Prix, when Pontiac puts this rear suspension into production, expect it to wear the Lumina's drum brakes. Whatever the actual brakes, the GPX and all Grand Prixs from '95 on get standard four-wheel ABS.

The increase to track width may restore the legendary Pontiac "Wide Track" look, but the chassis' actual dimensions are close to the current Grand Prix sedan's. The wheelbase has been extended 3 inches, from 107.5 to 110.5, but overall car length has grown only 1.2 inches. This slightly increases interior volume, most noticeably, rear-seat legroom, so the trunk space goes up only 0.5 cubic feet to 16.0.

The passenger cell is the least startling aspect of the entire vehicle. It improves on today's platform, with a well-balanced mix of performance and excellent passenger accommodation. Dual airbags are standard equipment. The show car has a rear console with integral (and hidden) stereo and headphone ports.

Inside, the GPX space is impressive, even for taller riders in the rear. Rear-seat passengers enjoy an aft center console with its own discrete stereo system, complete with jacks for headphones, cupholders and a "pommel grip" passenger assist handle, to help with entry and exit. While certainly stylish, this unique item isn't expected to make it into production Grand Prixs.

The driver's environment complements the sporty characteristics promised by the GPX's exterior. Comfortably deep bucket seats face dual airbags and a thick, leather-wrapped steering wheel with remote stereo controls. Instruments number only a few-a tach, speedo, coolant temperature, and fuel meter. Shoulder-belt height adjusters should ensure comfort, and visibility is excellent, especially forward, due to the hoodline's precipitous drop.

It's the wrapper around all of this mechanical goodness and interior comfort that's most striking. The curvaceous GPX blends Pontiac's historic strength in creating performance-oriented sport sedans with the distinctive flash and dash of a performance coupe. The current Grand Am's in fluence is clearly evident, especially from the rear and three-quarter views. The sloping roofline contributes to the integrated and sleek modern appearance. The desire was to offer the convenience and roominess of a sedan with the aggressive styling typically associated with a sport coupe. We loved the flare look and said so, and the Pontiac representatives on hand agreed. But notice how the flares extend into the front fascia and the rear doors? It's unlikely that those will make their way into production, since the doors will likely be shared with other GM divisions using the platform. Olds, Buick, and Chevy will want their own styling cues, not Pontiac's. More likely, the zippiest of Grand Prixs will get thermoplastic fender extensions similar to those used on the current GP.

300 GPX
Body Style···········2-door, 4-passenger
Vehicle configuration···········Front engine, front drive
Engine configuration···········Supercharged V-6, OHV,
2 valves/cylinder
Engine displ. ci/cc···········231/3785
  hp @ rpm, SAE net
···········300 @ 5500 rpm
  lb-ft @ rpm, SAE net
···········335 @ 3500 rpm
Transmission···········4-speed automatic
Axle ratio···········2.97:1
Wheelbase, in/mm···········110.5/2807
Length in/mm···········196.0/4978
Base curb weight, lb (est.)···········3400
Fuel capacity, gal···········16.0
Suspension, f/r···········MacPherson struts/struts
Steering···········Rack and pinion,
variable power assist
Brake, f/r···········Disc/disc, ABS
Wheels···········18x9.0, cast aluminium
Tires···········255/40ZR18 Goodyear Eagle
Acceleration, 0-60, sec···········5.8
Quarter mile, sec/mph···········14.3/98.2
Braking, 60-0 ft.···········116
Slalom, 600-ft, mph···········63.1

Our exclusive first drive in this hi-po Poncho left us wanting more. The 300-horsepower GPX accelerated like a Trans Am; 0-60 mph ticked by in 5.8 seconds, spot-on the time of our last 5.7- liter V-8 Trans Am road test, while the quarter mile flashed by in a fiery 14.3 seconds at 98.2 mph (particularly impressive for a front-driver). Braking via those big discs behind the show wheels was equally impressive; the car stopped from 60 mph in 116 feet. Perhaps best of all, the performance sound is as impressive as the new performance envelope. The free-flowing exhaust plumbs a fresh voice into the passenger cell, especially interesting at wide-open throttle. We hold few illusions that the production GPs will come out of the box with as powerful an exhaust note, but the GPX's voice was both satisfying and in concert with the car's performance ambitions. It's a real Woodward-Avenue-cruising musclecar, every bit an extension of the GTO philosophy.

In full-throttle driving style, the Torsen system's benefits are apparent. Whether during high-energy test passes at Texas World Speedway or blasting away from a stoplight, the steering wheel twisted slightly under the onslaught of torque, then settled in to track perfectly-no more torque steer than you'd expect with the current GP's base 140 horsepower, 3.1-liter V-6.

How does all this compare to such Pontiac performance legends as the GTO? Well, the '64 GTO took a loping 15.8 seconds to complete the quarter mile, attaining a 93.1-mph trap speed in the process. Heck, even the justly lauded '70½ Trans Am, with its Ram Air 400-cubic-inch V- 8, could only manage a quarter-mile clocking of 14.5 at 99 mph and a 0-60 time of 6.5 seconds. Obviously, the GPX doesn't just honor classic Pontiac muscle, it expands the legend.

In creating the 300 GPX, Pontiac endowed its concept with the comfort and people-friendliness of a four-door, the high style of a performance coupe-and the high performance of a Trans Am. That's more than any car from the classic musclecar era ever did. In fact, that's more than any musclecar ever set out to do. If the hopes, dreams, ambitions, and potential of the GPX are realized in the '97 Grand Prix, those rosy memories of the musclecar era are in for some serious reevaluation.

Pontiac has infused its latest concept car with styling cues reflecting familiar divisional design themes. The bulbous taillights and nestled rear decklid recall the Grand Am. The twin nostril nose recalls nearly every great Pontiac of the past. And the hoodscoops bring back Pontiac's legendary Ram Air heritage. If the GPX is an accurate preview and it should be-the '97 Grand Prix will be a stunning addition to Pontiac's lineup. Supercharged production cars will produce at least 250 horsepower, managed by a traction-control system.