Exhaust baffles seem like something of an irritating and superfluous doodad for something designed for absolute freedom and simplicity. But those simple, metal plates do more than keep the squirrels happy at the expense of your precious horsepower; they perform a vital function in preserving the forest that you call your playground.
An all-terrain vehicle's exhaust consists of four basic components: the outer casing, a perforated inner core tube, the matting or baffles that go in between and a spark arrestor plate that keeps sparks from spewing out of the tailpipe and burning ecology down. There are two types of baffle plates: those that go around the perforated inner tube and those that go through the middle of the muffler. The second type works by bouncing sound waves back toward the engine, instead of allowing them to shoot out of the engine.
Baffles do a fine job of controlling sound but they often have a detrimental effect on exhaust flow and power output. The same attributes that allow those baffles to catch sound and reflect it back toward the engine also tend to catch exhaust gases. At the very least they induce turbulence in the exhaust stream; at worst, they outright block exhaust flow. This is especially problematic on two-stroke engines, which rely on very precise exhaust tuning and good flow. Removing baffles will almost always net you a bit of horsepower and torque, since very rarely will they positively affect exhaust flow.
Exhaust baffles are there for a reason: namely, to make the engine acceptably quiet enough to operate in populated and controlled areas. At high rpm, even a fairly small gasoline engine can produce well more than 100 decibels -- loud enough to cause hearing damage to the driver and louder than is allowed on many approved trail sites. And small engines tend to produce a lot of high-frequency racket, which is far from pleasant sounding to most. Still, it's a subjective thing; some people like an engine that sounds like the apocalypse crashing in a canyon.
Some forestry services impose decibel limits on off-road vehicles. So, removing or drilling holes into your ATV's baffles may land you in trouble. But more importantly, removing the baffles could just as easily remove the forest itself when those hot sparks spewing from your exhaust set it on fire. State governments long ago mandated spark arrestors for all ATVs, and the baffles, in many cases, serve double-duty as both south dampeners and spark arrestors. In cases such as this, removing the baffle could not only cost you some cash in fines, but could cost you some considerable time in prison if your state's attorney can prove that the fire you caused cost someone his life.
