Honda Guide to VTEC

If you know anything about cars you have probably heard of VTEC. But do you actually know what it is, what it does, or what it stands for? This article is designed to teach you the in’s and out’s of VTEC. After you are done reading you will finally understand why people love thier VTEC engines so much.

Introduction to VTEC

VTEC (standing for Variable valve Timing and Electronic Lift Control) is a system developed by Honda to improve the combustion efficiency of its internal combustion engines throughout the RPM range. This was the first system of its kind and eventually led to

different types of variable valve timing and lift control systems that were later designed by other manufacturers (VVTL-i from Toyota, VarioCam Plus from Porsche, and so on). It was invented by Honda’s chief engine designer Kenichi Nagahiro.

In the regular four-stroke automobile engine, the intake and exhaust valves are actuated by lobes on a camshaft. The shape of the lobes determines the timing, lift and duration of each valve. Timing refers to when a valve is opened or closed with respect to the combustion cycle. Lift refers to how much the valve is opened. Duration refers to how long the valve is kept open. Due to the behavior of the gases (air and fuel mixture) before and after combustion, which have physical limitations on their flow, as well as their interaction with the ignition spark, the optimal valve timing, lift and duration settings under low RPM engine operations are very different from those under high RPM. Optimal low RPM valve timing, lift and duration settings would result in insufficient fuel and air at high RPM, thus greatly limiting engine power output. Conversely, optimal high RPM valve timing, lift and duration settings would result in very rough low RPM operation and difficult idling.

The ideal engine would have fully variable valve timing, lift and duration, in which the valves would always open at exactly the right point, lift high enough and stay open just the right amount of time for the engine speed in use. VTEC can be used not only for economy but also for performance.

In practice, a fully variable valve timing engine is difficult to design and implement. Attempts have been made, using solenoids to control valves instead of the typical
springs-and-cams setup, however these designs have not made it into production automobiles as they are very complicated and costly.

The opposite approach to variable timing is to produce a camshaft which is better suited to high RPM operation. This approach means that the vehicle will run very
poorly at low RPM (where most automobiles spend much of their time) and much better at high RPM. VTEC is the result of an effort to marry high RPM performance with low RPM stability.

This article is continued in another post about VTEC Engines…

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