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.
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).
If we been paying attention to the acronyms used by Honda, Toyota and BMW over
the last few years, we've probably noticed that the letter "V" has
become quite popular lately. We've got "VTEC" appearing in all the
Acura and Honda brochures and "VVTi" showing up in the majority of
Lexus and Toyota literature. Finally, beginning this year with select BMW 3
Series engines, a new Double VANOS system will be advertised.
do all these Vs have in common? Well, in case we don't already know (or haven't
yet guessed despite the monster hint in this column's title), the V stands for
valves or, more specifically, variable valve timing.
Before we can appreciate how important valve timing is, we have to understand how it
relates to engine operation. Remember that an engine is basically a glorified
air pump and, as such, the most effective way to increase horsepower and/or
efficiency is to increase an engine's ability to process air. There are a number
of ways to do this that range from altering the exhaust system to upgrading the
fuel system to installing a less-restrictive K&N air filter. Since an
engine's valves play a major role in how air gets in and out of the combustion
chamber, it makes sense to focus on them when looking to increase horsepower and
is exactly what Honda, Toyota and BMW have done in recent years. By using
advanced systems to alter the opening and closing of engine valves, they have
created more powerful and cleaning burning engines that require less fuel and
are relatively small in displacement.
we take a look at each of these variable valve-timing systems, let's rehash how
valve timing normally works. Until recently, a manufacturer used one or more
camshafts (plus some pushrods, lifters and rocker arms) to open and close an
engine's valves. The camshaft(s) was turned by a timing chain that connected to
the crankshaft. As engine rpms rose and fell, the crankshaft and camshaft would
turn faster or slower to keep valve timing relatively close to what was needed
for engine operation.
the dynamics of airflow through a combustion chamber change radically between
2,000 rpm and 6,000 rpm. Despite the manufacturer's best efforts, there was just
no way to maximize valve timing for high and low rpm with a simple
crankshaft-driven valve train. Instead, engineers had to develop a
"compromise" system that would allow an engine to start and run when
pulling out of the driveway but also allow for strong acceleration and highway
cruising at 70+ mph. Obviously, they were successful. However, because of the
"compromise" nature of standard valve train systems, few engines were
ever in their "sweet zone," which resulted in wasted fuel and reduced
valve timing has changed all that. By coming up with a way to alter valve timing
between high and low rpms, Honda, Toyota and BMW can now tune valve operation
for optimum performance and efficiency throughout the entire rev range.
was the first to offer what it called VTEC in its Acura-badged performance
models like the Integra GS-R and NSX (it has since worked its way into the
Prelude and even the lowly Civic). VTEC stands for Variable Valve Timing and
Lift Electronic Control. It basically uses two sets of camshaft profiles-one for
low and mid-range rpm and one for high rpm operation. An electronic switch
shifts between the two profiles at a specific rpm to increase peak horsepower
and improve torque. As a VTEC driver, you can both hear and feel the change when
the VTEC "kicks in" at higher rpm levels to improve performance. While
this system does not offer continuously variable valve timing, it can make the
most of high rpm operation while still providing solid driveability at lower rpm
levels. Honda is already working on a three-step VTEC system that will further
improve performance and efficiency across the engine rpm range.
saw the success Honda was having with VTEC (from both a functional and marketing
standpoint) but decided to go a different route. Instead of the on/off system
that VTEC employs, Toyota decided it wanted a continuously variable system that
would maximize valve timing throughout the rpm range. Dubbed VVTi for Variable
Valve Timing with intelligence (Is this a dig at Honda, suggesting their system
isn't intelligent?), Toyota uses a hydraulic rather than mechanical system to
alter the intake cam's phasing. The main difference from VTEC is that VVTi
maintains the same cam profile and alters only when the valves open and close in
relation to engine speed. Also, this system works only on the intake valve while
VTEC has two settings for the intake and the exhaust valves, which makes for a
more dramatic gain in peak power than VVTi can claim.
other manufacturers, including Ford, Lamborghini and Porsche have jumped on the
cam phasing bandwagon because it is a relatively cheap method of increasing
horsepower, torque and efficiency. BMW has also used a cam phasing system,
called VANOS (Variable Onckenwellen Steuerung) for several years. Like the other
manufacturers, this system only affected the intake cams. But, as of 1999, BMW
is offering its Double VANOS system on the new 3 Series. As you might have
guessed, Double VANOS manipulates both the intake and exhaust camshafts to
provide efficient operation at all rpms. This helps the new 328i, equipped with
a 2.8-liter inline six, develop 193 peak horsepower and 206 pound-feet of
torque. More impressive than the peak numbers, however, is the broad range of
useable power that goes along with this system. Take it from someone who's
driven the new 3 Series and who loves torquey engines-it works!
the benefits of variable valve timing become more apparent to both consumers and
manufacturers, you can expect to see it on just about every vehicle sold in
America. I suspect that in five years, variable valve timing will be like ABS or
side-impact beams: only really cheap cars won't have it.