Not since the legendary Buick Regal GNX, GMC Cyclone, or even the GMC Typhoon has a similarly quick, turbocharged American product existed. Unfortunately, Chevrolet's TrailBlazer Twin-Turbo exists only as a concept vehicle, and we can't give you an on-sale date. Yet. What we can offer is a behind-the-wheel view with a fully instrumented track test of this 400-hp engineering study. And we can report that this agile TrailBlazer and its twin-blown Vortec 4200 engine are being evaluated for production.
GM is a very different place nowadays from what it was even a year ago. Top management has been shaken up, and there are many new faces on deck, aiming to revitalize this sleepy giant. One such is Ron Kociba, GM Powertrain's chief engineer on the 4.2L inline-six. At Mid-Size Truck, there's another batch of engineers and techs that have the same goals under vehicle- line executive Tom Wallace.
Ask Fritz Indra, Powertrain's executive director of advanced engineering, why 400 horses are being extracted from a truck engine that makes 270 in production form, and he makes it sound like a logical extension of everyday engine-development work. "We just think 400 is a nice, reasonable number," he deadpans with his Austrian physics professor's accent. "And we were going after significantly more performance without changing the engine to a V-8."
"Of course, if we needed more, there's more to be had," adds a smiling, but equally dry Kociba. "The point was to demonstrate the bullet-proof nature of this engine with fairly minor modifications."
We were surprised to learn how little is changed to create this Bullitt Mustang-performance-equaling six, with its twin Aerodyne turbos and air-to-water intercooler. For example, the block, crank, head, head gasket, cams, and valve sizes remain virtually untouched. The extra breathing hardware adds but 45 lb to the engine's mass. The only critical mods were a switch to 8.5:1 pistons (from 10.1:1), the addition of piston-cooling oil squirters, shorter (by 2 mm) connecting rods, thicker piston pins, higher-flow oil pump and fuel injectors, and a freer-flowing exhaust system. As you'd expect, the 4L60-E four-speed transmission's internals required some beefing, and the transfer case was swapped for the ultra-tough all-wheel-drive unit found in the 6.0L V-8-powered Cadillac Escalade.