Some people say the 6 cylinder sounds a lot better than the 4 cylinder, so I found two acceleration videos of a 330i and a 440i (both stock exhaust) and found the 6 cylinder has a deeper roaring sound. But then I found a video of M550i (V8) and felt the I6 sounds better. So I wonder are there characteristics in engine sounds that are determined by the number of cylinders? (Update: added reference videos)
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