3-Stage VTEC is a multi-stage implementation of VTEC

VTEC

VTEC is a valvetrain system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. The VTEC system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda R&D engineer Ikuo Kajitani, and was the first system...

 and VTEC-E, (colloquially known as dual VTEC), is implemented in some 1995-present D series engines

Honda D engine

The D series inline 4-cylinder engines have been used in a variety of compact Honda models, most commonly the Honda Civic, CRX, Logo, Stream, and first-generation Integra. Its displacement ranges between 1.2 and 1.7 liters and is available in both SOHC and DOHC versions; with some equipped with...

, allowing the engine to achieve both fuel efficiency and power.

Stage 1 - 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 per cylinder

Cylinder (engine)

A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...

 in the 16-valve engine remains mostly closed to attain lean burn. The lean burn mode gets the air to fuel ratio above the 14.7:1 stoichiometric ratio and thus enables extra fuel saving. It is said that the valve which remains partially closed allows fuel to drip into the combustion chamber before ignition, which helps the leaner gas/air mixture to burn within the compressed cylinder, reducing hot spots from occurring atop the piston or valves. This creates a turbulent "swirling" in the air/gas mixture which improves combustion. An average of 30 km/l 30 km/L (70.6 mpgU.S.) can be achieved while in lean burn at a constant speed of 60 kilometre per hour.

Stage 2

From ~2500–5500 RPM, all of the engine's intake valves are used. The engine now operates like a normal fixed timing 16 valve engine.

Stage 3 - VTEC

From ~6000 RPM to the rev limiter

Rev limiter

A rev limiter is a device fitted to an internal combustion engine to restrict its maximum rotational speed. This is usually carried out to prevent damage to the engine, however sometimes these devices are fitted to prevent an engine reaching the point at which it develops maximum power...

, the engine's VTEC wild cam lobe is engaged, increasing performance and fuel consumption.