Originally Posted by Honda News

VTEC(R) (VARIABLE VALVE TIMING & LIFT ELECTRONIC CONTROL)

Acura's VTEC(R) (Variable Valve Timing and Lift Electronic Control) gives the TL and TL Type-S engines strong low speed torque and throttle response while enhancing high-rpm power.

At low speeds, the intake valves have lower lift and are open a comparatively short period of time during cylinder filling. At high rpm where breathing is critical, the valves switch to high-lift, long duration mode to deliver the best volumetric efficiency possible.

Both engines continue to use the 3-rocker VTEC system, which allows each of a given cylinder's intake valves to be controlled by its own low-speed cam lobe. (By comparison, with 2-rocker VTEC, both intake valves in a given cylinder are controlled by a single low-speed cam lobe). With different low-speed cam profiles for each intake valve, 3-rocker VTEC allows for staggered valve opening and lift, which promotes swirl in the combustion chambers, thereby improving efficiency. With better mixing in the cylinders, burn speed and combustion stability are improved.

When engine rpm reaches 4700 rpm (4950 rpm in the TL Type-S), the powertrain control module (PCM) triggers the opening of an electric spool valve that routes pressurized oil to small pistons in the intake valve rocker arms. These pistons slide into position to lock together the three intake rockers in each cylinder, which then follow a single high-lift, long-duration cam lobes. With the engine's intake valve lift and opening duration continuously adjusted to suit the operating engine speed, the TL benefits with a broad torque curve and superior peak power. The two engines feature different cam profiles, with the Type-S sharing the same higher lift and longer duration.