what can variable valve timing do for you?
February 8th, 2006To literally breathe new life into their anachronistic pushrod engines, GM has started adding variable valve timing which optimizes valve timing over a broader range of engine speeds. (Overhead camshaft engines started down this path over a decade ago).
Car and Driver has sampled the new engine and reports:
A variable-length intake plenum optimizes airflow, and a new variable-valve-timing system rotates the cam to crack open the intake valves (and yes, the exhaust valves, too) earlier or later depending on the motion of your right foot. That’s a first for “cam in block†engines, says GM. Snigger if you wish. Say that’s like being first out with a black-and-white plasma-screen TV, but pushrod cam phasing is a new wrinkle worth noting and a widget that even the Corvette doesn’t have. Ultimately, easier breathing is what the fuss is about, and the 3.9 revs hard and fast with an unusually crisp song that we’re unaccustomed to in GM’s pushrod V-6s. It also doesn’t gasp at the far end of the tach, winding to the 6200-rpm redline with a steady, consistent push.
Note that variable valve timing is a blanket term that can mean different things. Systems may have two stages or be infinitely variable, operate on one or both camshafts, change just timing or timing and lift, etc.