VTEC-E is a twist on the regular VTEC mechanism. Whereas VTEC's purpose can be more
or less summarized as: extracting high RPM performance while maintaining smooth low RPM operation, VTEC-E can be
summarized as: allow extremely lean fuel-air mixture at low RPMs in order to increase fuel economy. In other
words, VTEC technology is used to optimize different ends of the RPM range in the two different implementations
First, some background information. Fuel is mixed with air and then combusted in
cylinders to make torque. How much torque is generated is affected directly by how much and how well the fuel and
air are mixed together. Less fuel and more air is called
a "lean" mixture, the opposite is called a "rich" mixture. For low RPMs, a normal engine's intake charge velocity
is low enough that the fuel and air are not mixed together very well. To make up for the sub-optimal mixing effect,
a slightly rich fuel/air mixture (more fuel) is needed to maintain smooth operation. VTEC-E artificially
increases the intake charge velocity, which creates a swirling effect inside the cylinder. This promotes a very
good mixture of the fuel and air, thus allowing a lean fuel/air mixture to be used. The result of this is great
fuel economy when running at low RPMs. Indeed, the current Civic HX, a 2400lb coupe, is capable of 37cty/44hwy
fuel economy from a 115hp 1.6L VTEC-E engine. Now lets see how VTEC-E works in detail.
Unlike regular VTEC mechanisms, there aren't any extra cam lobes in a VTEC-E engine.
So each pair of valves works off of exactly two cam lobes. Since VTEC-E merely increases the low RPM intake charge
velocity, it is a mechanism that only affects the operation of the intake valves. VTEC-E is found only in SOHC
engines due to its economical intentions. All this means that we only have to look at the two intake cam lobes and
the associated rocker arms and valves in order to gain a full understanding of VTEC-E.
A non-VTEC-E engine normally has one single cam profile for the intake valves. A
VTEC-E engine has two different intake cam profiles. At low RPMs, each intake valve works from its own intake
cam profile. One of the intake cam profiles is very normal looking. The other one, however, is almost perfectly
round, with just enough profile to it so that it pushes the valve open just enough to avoid
pooling of fuel above the valve lip. Therefore at low RPM, only one intake valve is opening and closing. Most of
the intake fuel and air are squeezed through this one valve, resulting in a good swirling effect in the cylinder.
The swirling effect optimizes the fuel/air mixture, thus allowing a very lean mixture to be used.
As the RPMs increase, the demand for more fuel/air rises as well. Once a certain
RPM is reached (approximately 2500RPM for the Civic HX), the one-intake-valve configuration starts to become a
significant intake restriction. At this time, a solid pin is pushed through the two intake valve rocker arms,
thus binding the two rocker arms into a single unit. This causes both intake valves to open and close according
to the normal cam profile, while the almost-round cam profile is no longer used.
VTEC-E is some times confused to be just another high-RPM optimizing mechanism like
other VTEC variants. And there is some truth to this: since only one intake valve is used at low RPMs,
the one normal cam lobe is made to open that one valve slightly taller and for longer duration than if both intake
valves are used. At higher RPMs, both valves follow this same cam lobe so they are both opened slightly taller
and for longer duration. This results in a slight improvement in high RPM breathing compared to non-VTEC-E engines
and thus slightly more power. This is evident by comparing the Civic DX and Civic HX engine. The two engines are
essentially the same except for the VTEC-E in the Civic HX. But the Civic HX's VTEC-E mechanism results in 115hp,
versus 106hp from the Civic DX. So the Civic HX has more power in addition to better fuel economy. But make no
mistake, VTEC-E is designed with economy as the primary goal, not power output.
The info on this page is a copy of the webarchive.org pull of www.leecao.com, which at the time of this posting this (10/31/2007) was no longer a valid site.