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

Adding to what others have already said, rev range and displacement. (piston/cylinder size). 2 stroke dirt bikes have much smaller engine parts, and you can spin them faster before you start to run into problems.

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Harley motors are much bigger, and more reciprocating mass means lower rev ranges.

Answer 2

Harley has a patent on their engine that makes the sound.

And as others have said about the two stroke vs four stroke.

Answer 3

Displacement (engine) size. And the way the engine operates:
Dirtbikes are two stroke cycle and Harleys are four stroke cycle. HD has a much larger engine and exhaust systems
More fuel to air ratio.

Answer 4

First off, the high pitched and tinny dirt bike engines you’re thinking of were probably fairly small two stroke engines, while Harleys are big four stroke engines. That’s a big difference right there, but two stroke dirt bikes aren’t made anymore, so it’s one that has gone away. Modern four stroke dirt bikes have a much deeper sound than the old two stroke bikes, although the engines are still half the size of an average Harley engine or less most of the time, so they’re not as deep and loud as a typical Harley. They also have much different exhaust and rev a lot higher, so they sound different.

Answer 5

Some dirt bikes have two stroke engines and motorcycles are generally 4 stroke engines. Also mufflers are longer on motorcycles generally speaking

Answer 6

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.