Tech Injection: GM's Direct Injection V-6 and Active Front Steering

The General's most potent V-6 ever owes much of its newfound power and efficiency to direct fuel injection. As with all DI gasoline engines, much of the improvement is due to the fact that evaporating fuel cools the cylinder charge enough to allow higher compression (from 10.2:1 to 11.3:1) without knock-even on regular fuel. Fuel efficiency is also expected to improve very slightly, and by using a dish in the piston to corral a locally rich air-fuel mixture and modifying the injection strategy when the engine is cold, start-up emissions are shaved by a healthy 25 percent. Also of note is the fact that the injectors are mounted in flexible "cups" that isolate them from the cylinder head, so that their intense injection impulses don't cause the ticking noise common in other DI engines. They're also nestled in the valley and covered by other acoustic isolators. We detected nary a tick.

The other, perhaps more interesting techno-trick is StabiliTrak 3's new active front steering system. Instead of using a planetary gearset like BMW's does, one end of the steering column connects to an electric motor's rotor, the other to its stator. A spring-loaded steel pawl (like the thing that keeps an automatic transmission in park) connects the two in case of power or electronic failure as a safety measure. Otherwise, varying the current across this motor allows it to add or subtract from the amount of steering delivered to the rack. This system, by JTEKT, is said to suffer less lash or geartrain slop than the BMW-style units, and it is controllable to within 0.2-degree, so drivers never feel any notchiness as it works to maintain the driver's intended heading when loss of traction or other forces might otherwise send it off course. The system also includes a new performance mode to allow more tail-out shenanigans, but at launch it will only be available on all-wheel-drive models.