TWO-STROKE TUESDAY: THE SOUND & FURY

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FMF pipesFMF’s offerings at the Two-Stroke World Championship.

Motocross racers listen to their own bike, but unless they are racing a “run what you brung” class, most bikes sound similar to each other. Smokers have always sounded better than thumpers, but the diverse pops and pitches become more pronounced the more you hear the two side by side. Two-strokes can tell a lot more about their powerband. Most motocross riders are versed in the secondary language of “braap.” Only in moto do phrases like “It went burr burr braaaapp!” make complete sense. Whether you are conscious of it or not, “braap” is a two-stroke language.

A 450 National sounds like the LA Jackhammer Harmonics Choir. There isn’t much variance in the sound. It is simply just a small rumble and then a big one. The sound can get deafening if in the wrong place. Whether in Supercross or the Nationals, there are places you can stand that will register painful-to-hear sounds. That being said, the AMA does have a sound limit. During the pre-race inspection, the sound cannot exceed 112 decibels, and after the race it cannot exceed 113 decibels. If the machines go over that the penalty is losing your fastest qualifying time and most likely your gate pick. The reason why thumpers sound louder is that the sound they produce is of a lower frequency. That makes it more linear, so it travels farther. Many exhaust manufacturers offer inserts that can reduce the sound output down to 94 decibels, but an insert changes the power output of the bike.

Engine ICE

Two-strokes aren’t much quieter. They are, however, a lot more pleasant to listen to. It isn’t so much of a rumble as it is a buzz. The buzz isn’t ear-rattling like that of a bee in your ear, unless the silencer falls off your kid’s Cobra CX50. The noise isn’t as linear and has less range at its loudest point. The sound also makes the bike sound lighter. The rumble on a four-stroke is more akin to a heavy Harley roadster than a works two-stroke. The noises two-strokes make are vastly more diverse. Different parts of the powerband are more pronounced. If the fuel isn’t burning properly then it can be more audible. This may also be because two-strokes have much shorter powerbands. With a wider powerband the sound gradually rises, while a snappy two-stroke is more like to jump up.

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