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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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