Civic Si: i-VTEC Concept
The innovative Variable Valve Timing and Lift Electronic Control (VTEC) system delivers abundant low-rpm torque, exhilarating high-rpm power, and outstanding fuel efficiency. The Civic Si features the latest version of this remarkable engine system: i-VTEC. The "intelligent," i-VTEC system adds VTC (Variable Timing Control) to VTEC to provide continuously variable camshaft timing – taking the concept of variable valve timing to new heights. In the Civic Si, i-VTEC = VTEC + VTC. Not only does i-VTEC provide a substantial performance increase across a broad power band, it boosts fuel economy while also reducing engine emissions.

Civic Si: i-VTEC Valvetrain
The Civic Si engine uses an aluminum cylinder head and a dual overhead cam, four-valve-per-cylinder valvetrain incorporating the i-VTEC system. High performance camshafts are used that allow for aggressive intake and exhaust valve openings to boost the rate that air moves into and exhaust moves out of the cylinder. At high engine speeds, valve lift phase on the intake side is increased by five degrees and on the exhaust side by 10 degrees. The camshafts increase engine breathing and help deliver enhanced top-end horsepower. The camshafts are operated by a silent-chain drive that helps provide smooth, refined performance while also being maintenance-free.

The VTEC component to the innovative Civic Si i-VTEC system adjusts the lift and opening duration of the valves to help the engine produce both abundant low-rpm torque and excellent high-rpm power. At low rpm, VTEC provides valve timing and lift for optimum cylinder filling. In addition, the timing of the intake valves is staggered and their lift asymmetric-creating a swirl effect within the combustion chambers. The result is increased burn speed with improved combustion stability. As engine rpm builds, VTEC transitions to a high-lift, long-duration cam profile for improved high-rpm engine output.

The Civic Si uses a high performance version of VTEC that varies the lift and duration of both the intake and exhaust valves for maximum power output. At lower rpm, the valves follow low lift, short duration camshaft profiles to help boost low-end torque. Above 5,800 rpm, the intake and exhaust valves are operated by high-lift, long-duration cam profiles, for maximum high rpm horsepower. When combined with VTC, both versions help the Civic Si engine produce a remarkably broad and smooth power band with exceptional torque and horsepower.

Civic Si: VTC (Variable Timing Control)
The Civic Si's i-VTEC system adds VTC (Variable Timing Control) to VTEC for continuously variable camshaft phasing across the engine's entire power band. As engine rpm builds, a VTC actuator-controlled by an engine-control unit that monitors cam position, ignition timing, exhaust oxygen content, and throttle position-advances or retards the intake cam throughout the 50 degree range, optimizing engine output and reducing emissions.

During typical operation, the intake camshaft timing is almost fully retarded at idle to help provide more stable idling while reducing exhaust emissions (NOx). As rpm increases, the intake camshaft is advanced, opening the intake valve sooner and providing additional valve overlap. This results in increased fuel economy (by reducing pumping losses) and a further reduction in exhaust emissions (by creating a large, internal exhaust gas re-circulation effect). Also, to generate additional power throughout the rev range, the intake camshaft is continuously varying the amount of advance or retard, instantly adjusting to provide additional power as required by the driver.

Source: Honda PR