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Discussion Starter · #1 ·
Hey guys. Instead of working ive been sitting here wondering why exactly 3 cylinder engines have the awesome sound that they do. Especially what causes them to sound different than a comparitive 180 degree 4 cylinder. If someone could get technical in an explanation that would be great. From what I can figure, it obviously has to do with the firing order of a 120 degree crank. Im thinking it it also deals with how close together in time the combustion strokes occurs. Its almost as if you can hear each combustion stroke occur in a 3 cylinder (at idle speed) where as a 4 cylinder has more of a buzz.
 

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yes, it's the firing order, and that determines how close together in time each combustion is. in a triple you have a combustion every 240 degrees of crank rotation, on a (flat plane) inline four, it's every 180 degrees. so each bang is spaced out more on a triple at a given rpm than on a four.
 

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Discussion Starter · #3 ·
Okay one other question. Why does the 90 degree "cross plane" crank such as in the new R1s sound similar to ours? I know I'm missing something here. It seems counter intuitive to me that when the degrees between crank pins decrease, the pitch grows lower. I mean with a 90 degree crank, the time interval between combustion strokes is shorter than on the old R1 180 degree cranks. So why do the old R1s sound "buzzy" while the new ones have a similar throaty sound like the Fz?
 

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An inline 4 with a normal crank has evenly spaced power strokes. A cross plane 4 doesn't, same RPM the number of power strokes are the same, but some intervals are shorter, some longer.

How much it sounds like a triple I won't comment on lol. For the same total displacement fewer cylinders means larger individual cylinders, to my ear that gives a lower pitch I guess.
 
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