VTEC is one of Honda's greatest invention. Though an undisputed expert in turbo-charging as evidenced by years of Formula-1 domination while Honda was active in the sport, Honda's engineers feels that turbo charging has disadvantages, primarily bad fuel economy, that made it not totally suitable for street use. At the same time, the advantages of working with smaller engines meantthat smaller capacity engines with as high power output as possible (ie very high specific-output engines) are desirable for street engines. Thus Honda invented VTEC which allows it to extract turbo level specific output from its engines without having to suffer from the disadvantages of turbocharging (though VTEC introduces disadvantages of its own). The Basic VTEC Mechanism The basic mechanismused by hydraulically actuated pin. pushed horizontally to link spring mechanism is used to original position. the VTEC technology is a simple This pin is hydraulically up adjacent rocker arms. A return the pin back to its
The VTEC mechanism is covered in great detail elsewhere so it is redundant to go through the entire mechanism here. Instead we will look at the basic operating principleswhich can be used in later sections to explain the various implementations VTEC by Honda. To start on the basic principle, examine the simple diagram below. It comprises a camshaft with two cam-lobes side-byside. These lobes drives two side-by-side valve rocker arms.
The two cam/rocker pairs operates independently of each other. One of the two cam-lobes are intentionally drawn to be different.The one on the left has a "wilder" profile, it will open its valve earlier, open it more, and close it later, compared to the one on the right. Under normal operation, each pair of cam-lobe/rocker-arm assembly will work independently of each other.
VTEC uses the pin actuation mechanism to link the mild-cam rocker arm to the wild-cam rocker arm. This effectively makes the two rocker arms operateas one. This "composite" rocker arm(s) now clearly follows the wild-cam profile of the left rocker arm. This in essence is the basic working principle of all of Honda's VTEC engines.
Currently, Honda have implemented VTEC in four different configurations. For the rest of this feature, we will examine these four different implementations of VTEC.
DOHC VTEC The pinacle of VTEC implementation isthe DOHC VTEC engine. The first engine to benefit from VTEC is the legendary B16A, a 1595cc inline-4 16Valve DOHC engine with VTEC producing 160ps and first appearing in 1989 in the JDM Honda Integra XSi and RSi.
Examine the diagram of a typical Honda DOHC PGM-Fi non-VTEC engine on the left, in this case the 1590cc ZC DOHC engine. Note that each pair of cam-lobe and their corresponding rockerarms though adjacent, are spaced apart from each other.
In the DOHC VTEC implementation, Honda put an extra cam/rocker in between each pair of intake and exhaust lobes/rockers. The three cam/rocker assemblies are now next to each other. The new middle lobe is the "wild" race-tuned cam-lobe. Using VTEC to link up all three rocker arms together, Honda is able to use either the mild or the wildcam-lobes at will.
Note : Though the ZC and B16A are well-suited to illustrate the difference between plain-DOHC and DOHC-VTEC, the B16A engine is not derived from ZC. In fact, ZC and B16A have different bore and stroke. The same applies for the B18A and B18C engines used in the JDM Integra series. DOHC VTEC implementations can produce extremely high specific outputs. The B16A for standardstreet use first
produced 160ps and now 170ps. In the super-tuned B16B implementation used for the new JDM EK-series Honda Civic Type-R, 185ps was produced from the same 1595cc. DOHC VTEC can also easily offer competitive power outputs to turbo-charged engines for normal street use. For eg, the E-DC2 Integra Si-VTEC produces 180ps from the 1797cc DOHC VTEC B18C engine. This compares favorably to...