4-Cylinder i-VTEC
Ushering in a new era of performance technology, Honda's original VTEC (Variable Valve Timing and Lift Electronic Control) has been elevated to a new plateau with the introduction of i-VTEC. This "intelligent" form of the highly effective VTEC package adds a new element to the mix in the form of VTC (Variable Timing Control), which provides for continuously variable phasing of the intake camshaft.

The formidable pairing of VTEC and VTC results in several major improvements to drivability, including more horsepower and torque at lower rpm levels, enhanced fuel economy and significantly lower emissions.

The VTEC system on the new 2.4-liter DOHC four employs two rocker arms with friction-reducing roller followers for each pair of intake valves, along with an intake cam that has separate lobes configured to optimize both low- and high-speed operation. Depending on engine load and rpm, an electronic controller determines which cam profile will be used and exactly how each intake will operate.

At low revs, where low lift and shorter duration provide optimal operation, the timing of the two intakes is staggered and the lift asymmetrically skewed in favor of the primary valve. This helps to create a swirl effect within the combustion chamber that increases the efficiency of the burn process. At higher rpm, a hydraulically actuated spool valve causes a locking pin to engage the secondary rocker arm with the primary one, transitioning the secondary valve into a high-lift/long-duration mode that improves output on the top end.

VTC allows the timing of the intake camshaft to be continuously varied throughout the engine's entire rpm range. Along with helping boost power, VTC also provides a more stable idle (allowing idle speed to be reduced) and reduced pumping losses by effectively creating an internal EGR effect at low and mid engine speeds. The result is increased fuel economy and lowered NOx emissions. Operation of the VTC is electronically controlled and is determined by input from sensors that monitor rpm, timing, throttle opening, cam position and exhaust gases.

Depending on conditions, VTC can vary the phasing of the intake cam (change its position relative to the crankshaft) by +/- 25 degrees. VTC activation is accomplished hydraulically via a spool valve that sends high-pressure oil to passages in the cam's drive sprocket.

At idle, the timing is almost fully retarded to minimize valve overlap. In normal highway driving, the intake camshaft is advanced to provide overlap for EGR effect. With the throttle wide open, valve timing starts in an advanced condition at lower RPM and continuously changes to a retarded condition when redline is approached. This allows optimum cylinder scavenging and pumping efficiency and provides outstanding power and torque throughout the rpm range.