We recently spent a day at General Motor's top-secret proving grounds outside Detroit. We didn't have to jump over the barbwire fence or sneak past the guards. GM invited us to a technical briefing for some of its future technology, including engines, and we were told some of these technologies would likely make it into production vehicles within the next two to five model years. GM didn't want to reveal which vehicles would get the new goodies, however, even though we were allowed to drive mule vehicles fitted with the parts. These GMs were nothing more than test beds, according to the company, which wouldn't confirm or deny whether they'd get the upgrades.
Vortec 3500
It was shaping up to be a rather mundane trip to Detroit--until we spotted three heavily camouflaged pickup trucks parked among the mules. Upon closer inspection, we realized these were early prototypes for Chevrolet's S-10 replacement, the '04 Colorado. Having seen them only in spy shots, we were pleasantly surprised when GM told us we could drive each truck. A stern warning that we could write only about the powertrain performance preceded this accessibility. Under no circumstances could we pass along our impressions of interiors, exteriors, ride, or handling. But our initial reaction that there was no story was quickly refuted as we hit the test track.
Two engines will be available for the Colorado and its GMC brother, the Canyon, which replaces the GMC Sonoma. The base engine is a 2.8-liter I-4 that produces 170 horsepower and 177 lb-ft of torque. The optional is a 3.5-liter I-5 that makes a respectable 215 horsepower and 225 lb-ft of torque. Both are part of what GM calls its Vortec Inline Engine Family. The first is the 4.2-liter I-6 that appeared in late 2001 as the lone powerplant in the '02 Chevy TrailBlazer, GMC Envoy, and Olds Bravada (soon to be the '04 Buick Rainier). Producing a V-8-like 270 (275 for '03) horsepower and 275 lb-ft of torque, the Vortec 4200 won praise from journalists and buyers alike for its smooth operation and willing power delivery.
By design, the 2.8-liter I-4 and 3.5-liter I-5 use 75 percent of the same parts as the I-6. This will allow GM to spread engineering costs across several vehicle brands and models, and the engines can all be built on a common assembly line, saving money. One GM engineer describes the I-4 and I-5 as an I-6 with cylinders removed. Common parts include pistons and valvetrain. Key features of these inline engines are an aluminum block and cylinder head, double overhead camshafts, four valves per cylinder, variable exhaust valve timing, coil-on-plug ignition, and electronic throttle control.