Baffles are used in many applications, but they're particularly common in motorcycles because motorcycles have little else to muffle their engine noise. All baffles, regardless of the specific design, have one thing in common: stopping the direct flow of spent exhaust from the engine. By stopping the direct flow, the muffle the sound. Herein lies an inherent design dilemma. Restricting exhaust flow in a four-stroke motor robs the motor of horsepower and fuel efficiency. They do create a small amount of back pressure on the engine which builds torque, but too much will damage engine performance. Designers have to work with this trade-off. Here are a few different kinds of baffles.
The simplest kind of baffle is an exhaust pipe that is curved. The curve itself serves as a baffle. While nearly all motorcycle exhaust require the exhaust pipes to be plumbed with curves in them to deliver the exhaust to the back of the motorcycle in a logical and space-efficient manner, the curves also serve the purpose of a baffle.
While baffle designs are nearly limitless in theory, in practice most are perforated tubes inserted into the end of your motorcycles exhaust pipe(s). Most louvered baffles are a tube about 1 foot long and roughly 2 inches in diameter. The tube has a cap or partial cap at the end that forces spent exhaust through the louver openings, creating the baffling effect.
Almost all motorcycle baffles are "multi-chambered" baffles, because the baffle is one chamber and the actual exhaust pipe acts as a second chamber. But some baffles use this multi-chamber approach in the baffle itself. These baffles force exhaust into a perforated or louvered tube, where exhaust hits a cap. The exhaust is then forced through the perforations (holes) into a secondary or outer baffle. The outer baffle may generally performs the same function, but on a different scale. The outer baffle or chamber may employ a different design than the inner one.
Most exhaust baffles rely on exhaust packing---using fiberglass---to perform some of their sound damping. Some baffles rely on fiberglass packing as an integral means of baffling. So, the design is intended to force exhaust through fiberglass packing, rather than using packing just to deaden the sound that may reverberate between the baffle and the outer exhaust pipe. The packing is a primary, not a secondary design feature.
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