What differences make a dirt bike’s engine sound high-pitched and tinny, but something like a Harley-Davidson’s engine sound deep and rumbly?

Question

Edit: I’m referring more to those heavy cruising bikes than specifically Harleys, but it seems the engine traits are similar enough anyway.

So from what I’m getting from the answers, the reason heavy cruising bikes sound so deep compared to dirtbikes is primarily the resonance due to engine size as well as being a four-stroke design. And since the extra tinny-sounding two-strokes aren’t much of a thing anymore, it’s mostly due to engine size now. (With some influence from muffler design.)

Thanks for the answers!

In: Technology

Answer 1

Two stroke exhausts are technically called expansion chambers and are designed to provide back pressure at an optimum time to prevent fresh fuel from being pushed out of the combustion chamber. In other words, they are designed for performance, not sound. While the same concept is true with four strokes (to a lesser degree), I’d be willing to bet Harley puts a lot of research into getting those exhausts to sound sufficiently bad-ass to attract the dentists and lawyers that are impressed by such things.