Honda VTEC Engines Explained
VTEC stands for Variable Valve Timing and Lift Electronic Control. Honda developed this variable valvetrain system in order to offer efficiency and power in smaller engines. VTEC systems use two camshaft profiles, one for bottom end economy and another for top end performance. Nowadays a number of different types of variable valve timing are in use with different manufacturers, from BMW’s VANOS, to the widespread VVT-i system used by millions of new Toyotas every year.
But the air let into the engine was controlled mechanically in a fixed way. Ikuo Kajitani, widely believed to be the father of the VTEC engine, was employed in the First Design Department at the Tochgi center. He believed the solution was a system that altered the valve operation for high and low engine speeds. This was extensively tested and eventually evolved into the VTEC engine.
In typical Japanese fashion, Kajitani belied the the goals set about by Honda bosses had been too low. Honda already ad a 130 hp 1.6-liter DOHC engine on sale and his target of 140 hp or 90 hp per liter lacked ambition The like-minded Nobuhiko Kawamoto, then president of Honda Research, agreed and have him a new objective: 100 horsepower per liter. In April 1989, Honda’s new Integra was launched with a new DOHC/VTEC engine. It was not only very powerful, but it also idled more smoothly and had no staring problems. The word praised it for having the first valve mechanism that changed the timing and lift on the intake and exhaust sides simultaneously.
"It felt like a dream," Kajitani recalled. "Conventional engines in those days could only produce 70 or 80 horsepower per liter. But here we were, being asked to increase it all the way to 100 horses. It wasn't going to be easy.”
The engine came with a new high-density, high-strength sintered alloy pulley that reduced inertial load on the timing belt. Honda was also first to increase the diameter of the intake valve, from 30 to 33 mm.
For this small engine to have enough torque low in the rev range, it needed to have more “bang”. The low speed cam was changed changed from 35 degrees to 20/30 degrees ABDC (after bottom dead-center). Simply put, the valves would close early in the cycle.
Obviously, making three cam followers fit and work in the same space as just one was a big problem. Honda created a new high-carbon, high-chrome cast steel alloy that was almost half as strong for the cam shaft. For the exhaust valves, they had to make a nickel-based alloy that was more heat resistant.
The first Honda with VTEC sold in the US was actually the NSX, a supercar with he reliability of a Civic arriving in an era where Ferraris were notoriously unreliable. This had a 3-litre DOHC VTEC V6 with 270-hp. In the same period, Honda developed the double overhead cam VTEC for 1.8-, 2.0- and 2.2-liter 4-cylinder engines.
As their cars increased in popularity, Honda saw the VTEC name was a good marketing tool and created the single over head cam (SOHC) versions. These had only one camshaft controlling intake and exhaust and only the intake valves could be controlled by the system. This problem was resolved on the J37A4 engine, a V6 3.7-liter modern unit that uses an innovative shape or the rockers which allows it to contact two intake valves at once.
VTEC has evolved over the years into hybrid technology, VCM (Variable Cylinder Management) which is a form of cylinder deactivation and the computer-controlled i-VTEC. But the basic idea championed by mister Tochigi lives on.