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Pontiac Solstice
(2006) - All-American Roadster

Pontiac Solstice cutaway - click to enlarge

Since it was first introduced as a concept vehicle at the 2002 North American International Auto Show in Detroit , the Solstice has evoked a passionate response. Inspired by the pure driving experience offered by classic roadsters, the 2006 Pontiac Solstice delivers both the thrill of open-air driving with balanced performance and refinement at an attainable price.

Solstice delivers pure roadster performance through a powertrain that drives the rear wheels. It consists of a 2.4L Ecotec engine with variable valve timing and a standard close-ratio five-speed manual transmission. Later in the 2006 model year, an optional Hydra-Matic 5L40-E five-speed automatic transmission becomes available.

The 2.4L Ecotec four-cylinder is rated at 177 horsepower at 6600 rpm and 166 lb-ft of torque at 4800 rpm. That power is available throughout much of the rpm band, as approximately 90 percent of peak torque is available from 2400 rpm to 5600 rpm. And with Solstice’s curb weight of just 2,860 pounds, the 2.4L Ecotec engine helps give the vehicle a weight-to-horsepower ratio of nearly 16.2 to 1.

Balanced performance and economy are hallmarks of the Ecotec engine family, with the 2.4L engine offering unique features such as variable valve timing, coil-on-plug ignition, piston oil-cooling jets and integrated engine oil cooler. To accommodate the increased power level of the engine, the 2.4L Ecotec’s cylinder block bulkheads – the areas where the main bearing caps are attached – are enlarged for strength. Other areas of the engine were enhanced to reinforce the structure; the water jacket is deeper for added cooling capacity and improved cylinder bore roundness.

Pontiac Solstice cutaway - click to enlargeThe camshafts of the 2.4L engine have phasers that support the continuously variable intake and exhaust valve timing. They also have cam position sensors, so that the electronic control module can accurately control valve timing. The crankshaft and camshaft position sensors on the 2.4L engine are digital. The 2.4L engine also has premium features designed to ensure smooth and quiet operation, including a polymer coating and skirt design for the pistons that reduces noise during cold starts. An automatic hydraulic tensioner also is used; it maintains optimal tension on the timing chain, which reduces noise and vibration.

An Aisin five-speed manual transmission is standard on the Solstice. It features a 3.75:1 first gear, along with closely stepped higher gears that help keep the engine at the sweet spot in its power band during shifts. This contributes to a sportier driving feel and extracts maximum performance from the 2.4L Ecotec engine. Shifter feel and throw length is optimized to deliver short, precise shifts. First and second gears feature triple-cone synchronizers for a smoother shift feel.

Later in the ’06 model year, the advanced Hydra-Matic 5L40-E five-speed automatic transmission was offered as an option. As with the five-speed manual, the gear steps of the automatic complement the horsepower and torque bands of the engine.

The transmissions channel torque to an independent rearend that features a 3.91:1 axle ratio. The gears are housed in a rear axle derived from the Cadillac CTS, which was chosen for its excellent performance characteristics and high torque capability. A limited-slip rear differential is available. It uses a pre-loaded, friction clutch-type design and divides power equally between both rear wheels during normal driving conditions, but in low-traction conditions, the differential transfer torque to the wheel with better grip.

The foundation for Solstice’s responsive suspension system is a lower-dominant tube structure for the chassis. Hydroformed frame rails, which run the full length of the vehicle, are the basis of the chassis, while additional stampings form a rigid structure onto which the bodywork is attached. The hydroformed tube structure, which runs from the front bumper, through the left- and right-hand frame tubes and all the way to the rear bumper, provides an extremely strong foundation. Hydroformed tube structures have typically been used in light-duty truck frames and in some front-wheel drive vehicles, but Solstice is one of only two vehicles to feature an entire hydroformed chassis – the other being the Chevrolet Corvette.

The hydroforming process uses pressurized fluid to form each frame rail from a single piece of steel, rather than several pieces of steel welded together. This creates a stronger frame rail and requires less time to form it. Also, it provides a high strength-to-weight ratio, with additional components and stampings are added to the frame rail during vehicle assembly. A unique assembly method was adopted for the production of the chassis, with extensive use of MIG (metal inert gas) welding. Where typical automotive sheet metal assembly typically uses spot welding because of its speed through automation, MIG welding was selected to attach brackets and other chassis and body structures because the hydroformed frame tubes don’t allow access on the inside of the tube – and spot welding requires access to both sides of a piece of metal to create a weld. Although more time intensive, MIG welding allows parts to be joined with access to just one side.

A tunnel at the center of the chassis, which houses the transmission and driveshaft, is internally reinforced and enclosed at the bottom to enhance stiffness. This built-in strength reduces chassis flex and cowl-shake in a vehicle designed from the outset as a convertible. Solstice’s bending frequency is 20.9 Hz and the torsional frequency is 18.8 Hz –figures that compare with competitors at the top of the segment.

The strength of Solstice’s lower-dominant architecture means the body doesn’t have to carry much of the vehicle’s strength. This allowed for more exterior design flexibility, while also enabling precise suspension tuning.

The architecture’s rigid structure also permits more precision when it comes to tuning the suspension, as engineers don’t have to account for chassis flex. The short-long arm suspension design features forged aluminum upper and lower control arms that are strong and low in mass. The rear suspension also features a toe control link and the rear differential housing has an optimized three-point mounting design. Bilstein monotube shocks are used at each corner and provide immediate and controlled damping.

Solstice’s responsive suspension is linked to the road via 18 x 8-inch aluminum alloy wheels and P245/45R18 all-season tires. The wheels are mounted at the outer corners of the vehicles, enhancing grip and giving the vehicle an aggressive stance. The five-spoke wheels come standard with a painted finish and a bright polished version is available.

Four-wheel disc brakes are standard and consist of 11.7-inch (297 mm) ventilated front rotors and 10.9-inch (277 mm) rear rotors. ABS (with dynamic rear proportioning) is available. Power-assisted rack-and-pinion steering is standard. It features a 16.4:1 ratio and requires only 2.7 turns, lock to lock. The steering system is tuned to provide a confident “on center” feel and delivers excellent driver feedback, further enhancing the driver’s feeling of being connected to the road.

General Motors © 2006

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Pontiac Solstice

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