Today's four-stroke performance quads are completely different animals from the two-strokes of yesteryear, but there is no questioning that they now dominate ATV performance-market sales. Look at the ads from aftermarket performance companies, and you'll see that one thing hasn't changed since the days of the two-stroke machine: Almost every performance quad comes hamstrung from the factory, just a shadow of its potential self.
Although it works in entirely different ways between a two- and four-stroke machine, an exhaust pipe is still one of the best performance buys to be had for any quad. With that in mind, we were intrigued when asked by Vicious Cycle Performance (VCP) to examine and test its new Pulse Charger exhaust. According to the gang at VCP, just about every pipe offered today is fairly similar in design theory-more or less a modified "cherry bomb" muffler due to the size and packaging constraints of an ATV. In other words, when you peel off the graphics and stickers, you'll find most mufflers are an outer shell with a perforated tube running through the middle wrapped in fiberglass packing. There can be millions of permutations of this configuration, and some work better than others; but in terms of their design theory, they are remarkably similar. The desire to try something that could be new, different and better resulted in the genesis of VCP.
One proven performance concept for an exhaust is the megaphone style, which looks like a trumpet cone on the end of the exhaust pipe. The drawback is there is no-repeat no-sound silencing built in. Our ears are already ringing at the thought. Knowing that would be completely unacceptable, the designers at VCP wondered what would happen if they combined the best characteristics of the two proven but dissimilar types-the sound deadening of a packed muffler and the performance boost of a megaphone. Enter the Pulse Charger! It's constructed with a stepped header pipe for maximum exhaust velocity and contains a combination of megaphone and silencer technologies; VCP claims it offers the best of both worlds. We mounted it to a completely stock YFZ450 to see its capabilities.
What we noticed first is the Pulse Charger is quite a bit heavier than most other performance systems and sports a completely different look that people seem to either love or hate. The pipe and muffler bolted up easily, and we installed the recommended jetting after jettisoning the airbox lid. Strapped to the dyno, the Pulse Charger made a peak of 44.6 horsepower and 30.6 foot-pounds of torque, up from the stocker's 38.1 horses and 24.8 foot-pounds, respectable gains of 6.5 horsepower and 5.8 foot-pounds.
Out on the track and trail, the YFZ felt freshly alive and quite competitive with some of today's more popular exhausts. Throttle response was good, but the YFZ didn't seem to rev out as quickly as we expected. And we had a pair of serious complaints with our Pulse Charger. Due to the unique shape of the muffler, the headpipe has a bulge that comes farther forward than on any other pipe, which wasn't good for riders who like to lean back. After riding for a handful of hours, we found the packing of our Pulse Charger beginning to blow out at the seam near the end-cap. Naughty, naughty when you are asking big-boy money for your system.
With its weight and the boot-burning bulge, we don't expect the Pulse Charger to draw the MX crowd in droves, but we wouldn't be surprised to see the rocket launcher-jet turbine look catch on in the dunes, where the chromelike finish and high-quality materials of the VCP pipe can really shine.
InfoFull system: $675(Jetting: 168 main jet, fuel screw three turns out and needle on fourth clip)
Value:Dollars per hp: $103.85Dollars per ft-lb of torque: $116.38
Vicious Cycle Performance877/284-2468www.stealthcharger.com