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The Perfect Purr - How Does a Motorcycle’s Engine Affect Sound?

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The Perfect Purr - How Does a Motorcycle’s Engine Affect Sound?

Daniel Roberts

To roar or to purr – that is the question

Think of a motorcycle’s exhaust sound as its voice. It should not be so loud that you can’t hear yourself think. But it should not be so quiet that you hardly hear it.

Ideally, many bike enthusiasts agree that the sound of a bike should be a gentle rumbling purr, a satisfying sultry sound that displays the silent power of a strong engine. Here, we focus on how the engine determines the sound of a motorbike.

Let’s Start with the Cylinders…

Typically, motorcycles have two or four cylinders, but different motorcycles can have varying numbers of cylinders as well, going up to six cylinders.

A single cylinder would, of course, not make much of a sound, and would be reminiscent of a lawnmower. Bikes like the Triumph Bonneville or the BSA Lightening have a deeper sound, which many lovers of these British bikes like.

However, this sound changes when the cylinders are moved apart, like with a v-twin engine. Since the firing order is different, this type of engine has a shorter sound, very much like a V-8 engine. Bikes with a three-cylinder engine such as the Kawasaki H1 have more of a musical sound, because their crankpins are usually at 120 degrees.

Bikes with inline-four cylinders with flat crankshafts with crankpins at 180 degrees would produce a high-pitched sound, much like the well-known GSX-R screech.

And this goes on. With each engine, number of crankpins and cylinders, the sound changes.

What Else Affects the Sound?

Engine sound is also determined by how quickly an exhaust valve opens. For instance, if you have a two-stroke engine, the exhaust would be released fairly quickly, which in turn would produce that staple ring-ding sound that is reminiscent of two-stroke bikes.

However, if you have a four-stroke bike, you might be able to redesign your crankshaft so that the exhaust is released more slowly. This would result in a less steep sound, which would be easier to muffle.

All this can be done through effective acoustic engineering.

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Learning the Nature of Your Bike Engine

If you’re curious about your bike’s engine, you’ve come to the right place. We offer expert services for all your motorcycle needs, from vintage motorcycle restoration to basic custom fabrication services!

Contact us or call (908) 996-5337 to learn more about your bike and the different components that make it a classic.