What is I-VTEC?

The VTEC (Variable Valve Timing & Lift Electronic Control) system, developed by Honda, enhances the performance and fuel efficiency of four-stroke internal combustion engines. Unlike standard VVT systems, which only adjust valve timing, VTEC also changes the camshaft profile and valve lift. Invented by Honda engineer Ikuo Kajitani, the system utilizes multiple camshaft profiles and hydraulically selects between them to optimize engine performance at different RPMs.

Context and Description:

Japanese automakers, including Honda, have focused on improving smaller engine designs due to tax regulations based on engine displacement. While some manufacturers use forced induction or rotary engines to boost performance, Honda's VTEC system changes the cam timing profile in real time. The system uses two cam profiles: one for low-RPM efficiency and stability, and another for high-RPM power. The ECU controls the switch between these profiles based on several factors such as engine speed and load. This allows for optimal valve timing, lift, and duration at both low and high RPMs.

History:

VTEC originated from the REV system introduced on Honda's CBR400 motorcycle in 1983. The first automobile application was in the 1989 Honda Integra XSi with the B16A engine. It soon appeared in other models, such as the 1991 Acura NSX and 1992 Acura Integra GS-R. Honda has since developed various VTEC versions, including i-VTEC and i-VTEC Hybrid.

DOHC and SOHC VTEC:

- DOHC VTEC: First introduced in the B16A engine, it uses separate camshafts for intake and exhaust valves. This system provides high-RPM power while maintaining low-RPM efficiency.

- SOHC VTEC: Applied to engines with a single camshaft, affecting only the intake valves due to spatial constraints. Innovations in engines like the J37A2 have allowed for VTEC on both intake and exhaust valves.

VTEC-E:

This variation focuses on improving combustion efficiency at low RPM while maintaining mid-range performance. The initial VTEC-E used two different cam profiles per cylinder to optimize fuel mixture. Later versions combined these benefits with high-performance capabilities, using three cam lobes per cylinder to provide both low-RPM efficiency and high-RPM power.

In summary, Honda's VTEC system enhances engine performance across a range of operating conditions by dynamically adjusting valve timing, lift, and duration. This innovation has enabled Honda to produce engines that are both powerful and fuel-efficient.