By: Kong-Ngai Wong
VTEC is one of Honda's greatest invention. Though an undisputed expert in
turbocharging as evidenced by years of Formula-1 domination while Honda was
active in the sport, Honda's engineers feels that turbocharging 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
meant that 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 Temple of VTEC is specifically created by Jeff Palmer as a dedication to
this great technology and the Temple of VTEC Asia is dedicated to the home of
VTEC -and of Honda, Japan and the region of Asia.
In this permanent feature, we will examine the basic mechanism that make up
the VTEC technology as well as the various implementations of VTEC.
The Basic VTEC Mechanism
The basic mechanism used by the VTEC technology is a simple
hydraulically actuated pin. This pin is hydraulically pushed horizontally
to link up adjacent rocker arms. A spring mechanism is used to return the
pin back to its original position.
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 principles which 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-by-side. 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
operate as 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