VTEC. Four letters that practically started a revolution. To Honda's engineers, it means Variable Valve Timing and Lift Electronic Control. But for some of us it sparks thoughts of many other things: space age-sounding technology, the unmistakable sound of a VTEC motor revving up, the innovation that yielded naturally aspirated engines 100 hp/liter before any other manufacturer-the very technology that arguably could have launched the sport compact scene in the early-'90s. But there's quite a bit more to it than that. VTEC innovations are evolving and constantly leaving their mark in the automotive world.
So how did it all begin? Variable valve timing, a technology adapted by many different automobile manufacturers, was a spin-off of another Honda project back in the early-'80s. At the time Honda's main goal was to create motors with decent power and excellent fuel economy. With the technology of the time, Honda engineers had already hit 50 mpg with the company's ultralow emissions CVCC technology, but Honda wanted more. By January 1983 a group of engineers were studying varying valve timing to improve mileage, but in October 1983 that team was split, with one group moving on to study more efficient fuel delivery systems and the other working on valvetrain technology.
The team responsible for fuel efficiency launched its NCE (New Concept Engine) project in March 1984. It was completed in 1985 with the release of fuel-efficient, low-emissions engines that had torque at low and high rpm and noticeable increases in horsepower-per-liter, 81 to be exact. These DOHC four-valve-per-cylinder engines found their way into the 1985 Integra and Civic and paved the way to even higher aspirations.
The NCE taskforce was reassigned to the D-development project in November 1986. Under the guidance of Ikuo Kajitani, the team's goal was to create a 100-hp/liter engine for the 1989 Integra.
At the same time, the valvetrain team was evaluating the Revolution-modulated Valve-control (REV) technology used in the 1983 Honda motorcycle, the CBR 400F. This technology allowed the four-valve head to operate with just two valves per cylinder for fuel economy at low rpm. A sensor detected engine speed and hydraulically controlled the locker arms, which at higher rpm would lock together with a pin, activating all four valves.
The team refined this technology over the next few years, eventually creating VTEC, which not only has variable valve timing, but also variable lift. Instead of turning off two valves during low rpm driving, as was the case with REV, the DOHC VTEC system employs all four valves at all times. The camshaft design had three lobes per cylinder, two low cam lobes and one high cam lobe. The two low cam lobes were tuned for drivability and economy. The high cam lobe actuated a cam follower that was disconnected from the two cam followers that actuated the valves while at low rpm. When the motor reached higher engine speeds, a VTEC solenoid sent hydraulic pressure to locking pins that connect all three cam followers. At this point, only the radical third cam lobe actuated the valves for timing and lift. The increased timing and lift increased airflow in and out of the cylinders at high speed, increasing power output.
By Richard Fong
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