2005 Pontiac Grand Prix GXP
Bob Plunkett
Date Posted: 8/2/2005
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ROSE BUD, Ark. -- A nifty LED screen on the dash of Pontiac's new V8-powered Grand Prix GXP sports sedan displays maximum G-force scores for accelerating, decelerating (braking) as well as lateral accelerating, or cornering.
What's a G-force score?
It's a measure of inertial force or the tug of gravity exerted on an object undergoing rapid movement. A score of 1.0 G is the gravitational pulling force equalivent to the entire weight of the dynamic object.
The G-force read-out in Grand Prix GXP won't work while the vehicle is moving, so you can't stomp on the accelerator and instantly find out how many G's your tire-screaming send-off is pulling, but when you stop the car the display will show what you've accomplished.
We pick an empty expanse of asphalt in pine-clad foothills of the Ozark Mountains of Arkansas to run a GXP through an orange-coned autocross course, then check the G-force scores on the LED screen to find out how quick and agile this new car can be.
Our starting-line blast-off acceleration -- drawing from the equivalent strength of more than 300 horses -- rates a score of 0.74 G.
Our best G-force deceleration comes at the first corkscrew corner, where we stand on the brake pedal hard enough to activate the Bosch four-channel anti-lock brake system (ABS). That move prompts a big decel score of 1.28 G.
And the corkscrew corner, tightest turn on the autocross lot, merits our best G-force measure of lateral acceleration with a reading of 0.75 G.
We find other high-tech instruments aboard the GXP Grand Prix to tell us how good we're running, as the driver's view through the windshield encompasses a head-up display with digital data indicating the vehicle's speed and operation of devices like the turn indicators.
Further, the GXP has two thumb-sized paddles -- labeled TAPshift for Touch Activated Power -- mounted on right and left spokes of the steering wheel.
A shift-it-yourself kind of driver can use the thumb and forefinger to move the paddles forward or backward and step up or down the powertrain's gear ladder in the same way race drivers control their open-wheel machines with finger-flicking upshifts and downshifts -- while keeping a proper two-handed grip on the steering wheel.
Core component that forges the GXP edition of Grand Prix is a new 5.3-liter aluminum V8 engine.
The overhead-valve V8, with high-flow cylinder heads similar to those found in the 6.0-liter LS2 V8 of Corvette, delivers 303 hp at 5600 rpm and big-time torque of 323 lb-ft at 4400 rpm.
That muscle produces quick acceleration for GXP, with a zero-to-60 mph time clipping under six seconds.
And the engine marks the first Grand Prix since 1987 to offer a V8 and the first Pontiac to apply GM's innovative Displacement on Demand (DOD) technology.
The engine's DOD wizardry automatically -- and seamlessly -- pares the number of cylinders engaged in the combustion process when boosted power is not needed.
For the V8 it means cutting back to a four-cylinder mode under light-load situations in a process which improves fuel economy numbers by as much as 12 percent.
Transmission is the efficient GM Hydra-Matic 4T65-E automatic with four forward speeds and the TAPshift paddles added.
But there's more working on the GXP Grand Prix than that sophisticated DOD V8 because re-tuning of the suspension drops the chassis about 9 mm for the road-hugging posture of a hunkered sports car.
Suspension modifications range from higher rate springs and Bilstein gas-charged struts for firm damping control to a hollow rear stabilizer bar at 17.2 mm for blocking body roll in tight corners.
For steering control, GXP gets GM's Magnasteer II variable-effort device with electronic controls for magnetic torsion to raise or lower the amount of effort required to turn the front wheels.
The high-performance disc brake system features aluminum calipers with vented and cross-drilled rotors.
Safety mechanisms include the Bosch ABS with electronic brake force distribution (EBD) and StabiliTrak, a four-wheel vehicle stability system that enhances tire traction during cornering maneuvers.
And GXP rolls on 18-inch forged aluminum wheels capped by high-performance tires.
The 18x8-inch front wheels carry P255/45R18 W-rated tires, with 18x7-inch rear rollers wrapped by P225/50R18 rubber.
Wide-track GXP looks like a serious performer too.
It sports new fascia up front, the twin-port grille ringed by chrome with honeycomb mesh inserts and bold low air inlets positioned between corner foglamps.
Flanks wear curvy rocker extensions and quarter-round honeycomb mesh engine vents, while at the tail there's a spoiler flying off the trunk deck and a thick new fascia wrapping tightly around rear corners with two sets of twin tailpipes tipped in chrome.
The design for GXP's cockpit brings innovations like flexible flip-and-fold seats and a generous cargo compartment in the rear plus back doors that swing wide -- virtually at a right angle -- to make broad portals that accommodate big loads of shopping gear such as a crate containing a television or desktop computer.
Layout for the cabin sets a pair of sport bucket seats up front and a bench for three in back.
The back of the right front bucket folds forward to form a flat horizontal surface, and backs of the rear bench, split into two sections of 60/40 percent, also fold flat on the same plane as the folded front seatback.
Cargo items as long as a nine-foot kayak or bulky snowboards may be loaded on top of these folded seats and extended from the dashboard rearward to the trunk's back bulkhead.
Large round analog gauges decorate the dashboard instrument panel, yet the driver may also view instruments as reflected off the windshield in the head-up display.
Seats are clad in leather with Ultralux suede inserts.
Brushed aluminum is used as trim accents on console and doors, with brushed aluminum doorsill plates.
Pontiac sets the MSRP for Grand Prix GXP at $29,335.
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| 2005 PONTIAC GRAND PRIX GXP VEHICLE SPECIFICATIONS |
| Description: |
Mid-size sports sedan |
| Model Options: |
Mid-size sports sedan |
| Wheelbase: |
110.5 inches |
| Overall Length: |
198.3 inches |
| Engine Size: |
OHV 5.3-L V8/DOD |
| Drive: |
Front |
| Braking: |
Power 4-disc, ABS/EBD/StabiliTrak |
| Airbags: |
2 (front) plus opt. 4 (side curtain) |
| Gas Mileage: |
city/hwy. 18/27 mpg |
| MSRP Price: |
$ 29,335 |
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