FAQ:

How does VTEC Work?

Information:

Honda's VTEC (Variable Valve Timing and Electronic Lift Control) system depends on a cleverly designed valve rocker system paired up with a unique camshaft. In an B-Series Honda engine (Ex. Integra GS-R's B18C1) there are 24 of these rockers equaling to six for each cylinder. This means that there are three on the intake side and three on the exhaust side for each cylinder. (An example is shown below)

The pins you see between the rockers are the pins that engage the middle rocker when the computer feels the engine should enable VTEC. The pins move back and forth depending on oil pressure coming through the passages from the rocker shaft. The oil pressure is controlled by a solenoid that is operated by the car's computer.

Unlike conventional rockers which have a pivot point in the middle of the rocker, these have their pivot point at one end. On the far end of the Primary and Secondary Rockers there are extensions with adjusting screws and locknuts. These rockers each operate a valve. The camshaft in this system is positioned on top of the rockers, and there are three lobes on the cam for each set of three rockers. Each cam lobe has a different contour and lift. The lobe of the secondary cam on a B18C1 is 1.27mm higher than the primary on the exhaust side for instance, and the mid cam is 2.609mm higher. The primary and secondary cams have a "mild" contour for smooth low speed operation. One operates its rocker and opens its valve slightly before the other on the intake side to impart a swirling action to the incoming fuel/air mixture, for combustion efficiency.

When operating at low RPM's all three rockers will move independently. The middle rocker will not be engaged by the pins meaning that is has no effect on the valves opening and closing. When you add this all together you get an engine that has a flat torque curve. This means that from 3000 RPM to 8000 RPM the torque curve is steady allowing for you to out perform normal cars that run out of air and drop off torque around 6000 RPM.

Below is an animation that will help illustrate the process in more depth.