VTEC stands for Variable Valve Timing and Electronic Lift Control and was Honda’s answer to increasing power from small capacity engines. Due to tax implications, the Japanese manufacturers needed to producer smaller engines than their European or American competitors but needed to have similar power and performance. Other manufacturers used turbos or rotary engines, Honda extended the development of REV (Revolution modulated valve control) that was originally fitted to a CBR400 motorcycle engine in the early 1980s. This technology used two valves at low speeds and four at high speeds.
Like variable geometry turbos that adjust themselves for different rev ranges, so does a VTEC engine. Overhead cam engines need different shaped cams for specific power outputs and usage. A low revving engine will have a different shaped cam lobe to a racing engine that spends more time at higher revs and needs the valves open longer and wider.
So Honda developed a camshaft that uses a solenoid to move a pin at a particular speed and locks either the low speed cam lobe or a high speed lobe. The engine has two rocker arms per cylinder with two low speed lobes sandwiching a high speed lobe. At low revs the low speed lobes are used but at a given point (approximately 6,000 revs on the S2000) the pin is moved to lock in the middle high speed lobe that is larger than the two either side, thus opening the valve further and longer.
The solenoid is activated by the ECU that is monitoring revs, throttle, oil pressure and engine temperature. Honda has developed SOHC cams with the two lobes for input only and DOHC cams (as seen on the NSX and S2000) that have one cam for input and one for the output, both with high and low speed lobes.
The 1989 Integra model was the first car to use VTEC and Honda have now produced VTEC engines for cars, motorcycles and marine engines and have also looked at how to apply this for low speed engines (VTEC-E) where only one intake vale is opened at low speeds and then at higher speeds both intake valves are used.
Current generation VTEC, i-VTEC and Advanced VTEC engines are optimised for performance and also emission controls to meet ever-stricter industry & Government regulations.