Three-stage VTEC is a multi-stage implementation of Honda's

VTEC VTEC (Variable Valve Timing & Lift Electronic Control) is a system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine, resulting in higher performance at high RPM, and lower fuel consumption at low ...

and VTEC-E (colloquially known as dual VTEC) technology, implemented in some of the company's D series engines from 1995 to the present day, allowing the engine to achieve both

fuel efficiency Fuel efficiency is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical potential energy contained in a carrier (fuel) into kinetic energy or work. Overall fuel efficiency may vary per device, wh ...

and power. VTEC-E (for "Efficiency") is a form of VTEC that closes off one intake valve at low RPMs to give good economy at low power levels, while "VTEC" is a mode that allows for greater power at high RPMs, while giving relatively efficient performance at "normal" operating speeds. "Three-stage VTEC" gives both types in one engine, at the cost of greater complexity and expense.

Stage 1 – 12-valve VTEC-E

VTEC-E (economy) was designed to achieve better fuel economy, at the cost of performance. The engine operates in "12-valve mode", where one

intake valve A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapor flow into an engine. It consists of a hole or open-ended chamber, usually round or oval in cross-section, and a plug, usual ...

per

cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infin ...

in the 16-valve engine remains mostly closed to attain

lean burn Lean-burn refers to the burning of fuel with an excess of air in an internal combustion engine. In lean-burn engines the air:fuel ratio may be as lean as 65:1 (by mass). The air / fuel ratio needed to stoichiometrically combust gasoline, by con ...

. The lean burn mode gets the

air to fuel ratio The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...

above the 14.7:1

stoichiometric Stoichiometry refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equal ...

ratio and thus enables extra fuel saving. This works similarly to the principle which gave the Buick "Nailhead" V8 its reputation for high torque (in that case, the engine had notably small intake valves, giving good torque, but limiting peak power). In an engine running at lower RPMs, a smaller intake valve area forces a given volume of air to flow into the chamber faster; this causes the fuel to atomize better, and therefore burn far more efficiently. An average of can be achieved while in lean burn at a constant speed of .

Stage 2 – 16 valve

At about 2500RPM and further the engine is able to switch to the 16-valve mode, which is usual to the classic engines. The first VTEC solenoid is opened and directs the oil to the sliding pin that connects the rocker arms of the intake valves with the first intake valve's lobe. Thus all the two intake valves are moving at the normal profile of that lobe. The engine's performance is usual to the non-VTEC engines. This mode is suitable for mid-range RPMs.

Stage 3 – 16-valve VTEC

From ~5200 RPM to the

rev limiter A rev limiter is a device fitted in modern vehicles that have internal combustion engines. They are intended to protect an engine by restricting its maximum rotational speed, measured in revolutions per minute (RPM). Rev limiters are pre-set by th ...

, the engine's high-lift VTEC cam lobe is engaged. A higher lift lowers restriction even more, giving the highest airflow. If one built a non-VTEC engine to make the maximum power, the trade-off would be very low efficiency at low RPMs in order to get the most flow possible at high RPMs. A three-stage allows the engine to run in "economy", "standard", and "high power" modes, while a VTEC only gives "standard" and "high power", and a VTEC-E only gives "economy" and "standard".

References

{{Reflist Variable valve timing Honda engines Engine technology