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By: Jason Giacchino
January 2010 - Off The Pegs
The Era of Virtual
Power
The scene is an outdoor motocross track, and
the leaders are approaching the very corner you
happen to be posted near. In true form, they
brake early then accelerate hard out of said
corner. The sound of whining two-strokes
fills the air, and the riders hang precariously
from the inside of their quads in an effort to
get a good bite into the next section. The roost
sprays out like rain, and the scream of the
exhaust note emanating from the pipe letting
everyone know that the throttle’s pegged wide
open. It’s the clutch controlling the
amount of wheel spin down below. The riders swap
left, right, then left again while trying to get
the wildly spinning rear tires to settle down
and then, as quickly as it all began, the pack
is gone in a cloud of dust and blue smoke toward
the next corner.
This was a very common scene just a few years
ago and while the life cycle of the two-stroke
engine is certainly at its twilight, there are
few who will remember that brutal hard hit of
acceleration, screaming engine, or mandatory
clutch control without a smile. The two-stroke
was wild, it was pipey, it was simple, and it
was fun: efficient, not so much.
The modern crop of riders and racers coming up
through the ranks will likely not have given a
passing thought to the simplicity or the unique
experience of racing a performance-oriented
two-cycle, because with the rejuvenation of
4-stroke technology, the manufacturers are
realizing that efficiency in power delivery has
a lot more to do with winning races than maximum
horsepower numbers or acceleration so violent
that the rider has to focus simply on hanging on
for dear life.
Insiders are calling this era the period of
“virtual power,” and the name fits. Whereas once
upon a time the only way to achieve engine
performance increases was through physical means
(pipes, jetting, valves, bore & stroke jobs and
so on), these days tuners have the ability to
tweak just about any area of an engine’s
performance by simply plugging in their laptop.
To thank for this shift from physical to digital
are technologies such as programmable ignition
maps, fuel injection delivery curves, and pretty
soon, programmable TPS (throttle position
sensors). Whereas a carburetor is a mechanical
device whereby pulling a cable on your
handlebars opens a slide that allows more fuel
to enter the engine and hence increase
acceleration, fuel injection does away with many
of the simple, manual aspects of the process.
The throttle is no longer just the lever that
pulls the cable, but rather acts like a rheostat
light switch in that it’s position and the speed
at which it is applied sends a signal to the
computer which then allocates the amount of fuel
to be injected (via a pressurized hose) into the
engine. The beauty of it is that when done
correctly, the rider can barely tell the
difference between the two despite the fact that
the processes are quite dissimilar.
What a rider may not notice, however, is that
greater factory attention is being paid each
year on the way the ATV’s engine gets that power
to the ground. Sure the two-stroke’s all-at-once
method of delivering power was wild and
exhilarating, the truth of the matter is that
less wheel-spin and smoother acceleration could
literally carve seconds from lap times.
Using the quad’s computer to compensate for
rider inaccuracy is a method being used on the
pro circuit right now with surprising results.
How does that work, you wonder? Well, imagine
that you went into a tight corner far too hot
and heavy, locked up the brakes to avoid blowing
the berm, then jammed the throttle wide open to
accelerate hard out of the apex. The computer
could be programmed to understand that such a
violent application of the throttle would do
little more than cause you to lose traction (or
in other words simply cause your tires to spin
without the quad gaining momentum).
Rather than simply allow the full blast of fuel
to flow into the engine that would normally
coincide with that throttle position, it could
meter the delivery to build revs more
efficiently. In this way the throttle suddenly
acts like the slowly released clutch of our
two-stroke rider trying to control the wheel
spin of his wide-open engine.
With a smooth, predictable acceleration (torque)
curve lap after lap, the rider is able to make
the most of his motor’s power with strong, hard
bites out of each and every corner. Sure it may
not be as dramatic-looking as the two-stroke
rider of yesteryear with one leg sticking out
across the saddle in a crouch off to the other
side in an effort to muscle his machine through
the corner, it’s been proven that fighting with
the machine all around the course only leads to
premature fatigue anyway.
The point is that while the modern four-stroke
has its detractors (increased cost, weight, and
complexity); it is refreshing to note that
engineers and tuners alike are making massive
strides in turning that technology into results
that can be realized by racers of all skill
levels.
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