Motown Muscle

In Detroit this year, the North American International Auto Show recorded its 100th anniversary, and the city joined in on the celebration as the domestic automakers hogged the spotlight. General Motors won both the Car and Truck of the Year awards with the Saturn Aura and Chevrolet Silverado-the first time in history that one manufacturer swept both categories. Ford and Chrysler generated plenty of attention with their new hardware as well. It was a very good show for Detroit, in Detroit.

Naturally, the mainstream media focused on Detroit's leading-edge efforts in hybrid, electric, alternative-fuel, and high-mileage vehicles. But the same green technologies that have boosted efficiency and reduced emissions have spun off an additional benefit just for us: lots of horsepower. While only a few years ago, 500 hp in a production vehicle was unthinkable, thanks to all these advances, that number has become the new baseline. Suddenly, a manufacturer is not a serious player in the Motown horsepower wars unless it has a 500hp engine in its lineup. And now, Detroit has raised the bar again, this time all the way up to 600 hp in a single jump.

Chrysler
Dodge is the first to blow past the 500hp benchmark and officially raise the ante to 600 hp with its new Viper. Formally launched at the Detroit show as an '08 model, the new-and-improved snake goes on sale this summer. The Viper's old truck-based V-10 engine has evolved a bunch since it was introduced in 1992 and even since the previous (third-gen) version was revamped for 2003-the one rated at 500 hp. "It's the same architecture but almost every part has been touched," says SRT Engine Team Supervisor Kraig Courtney, whose group developed the powerplant with engineering input from Ricardo and McLaren Performance Technologies. The displacement is now up to 8.4 liters due to a 1.0mm bore increase, but that's mainly so the V-10 can share the forged pistons and cracked connecting rods of the 6.1 Hemi V-8. The real keys to the big power boost are in the cylinder heads and valvetrain. "We've used the classic racing-engine strategy: make more power with airflow and rpm," Courtney says.

The new cast-aluminum cylinder heads sport CNC-cut combustion chambers, and the valve angle has been reduced from 18 to 12 degrees. Intake-port cross-sectional area has been increased 13 percent for 23 percent greater airflow, while the exhaust ports are up 13 and 10 percent, respectively. A freer-flowing intake manifold uses a pair of 74mm throttle bodies (borrowed from the 4.7L V-8) with fly-by-wire control. There is a revised airbox, a new Motorola CPU that is 10 times faster with 100 times the processing power, and the redesigned roller lifters have been lightened 28 grams each. But easily the trickiest and most intriguing piece in this new engine is the camshaft.

Any rodder who has degreed a camshaft is familiar with lobe separation angle (LSA). A defining factor in engine performance, LSA is the angle between the intake and exhaust lobe centerlines, and on a single-cam engine, it is locked in when the camshaft is manufactured. A wide LSA is generally good for low-end torque, driveability, and emissions, while a narrow LSA means increased overlap and usually better top-end power. When you select a camshaft, you unfortunately have to pick one or the other or settle for a compromise somewhere in the middle-until now, that is. No such compromises are required in the Viper V-10, which uses a novel form of variable valve timing (VVT) Chrysler calls CamInCam.