Today there are so many different engines and exhausts out there that it would take a whole book to explain each and every one of them in terms of how loud or quiet they are. Luckily, there is a very simple formula Total Motorcycle uses to figure it all out. And we will get to that in a moment.

Lets talk basics first. The loudest main noise that comes off a motorcycle is from the exhaust. If anything makes noise louder than the exhaust I'd suggest walking away from that bike..haha

Exhausts dB (Decibels (noise level)) is governed by the government not to exceed certain levels. Unfortunately, these laws are rarely enforced for aftermarket exhausts.

There are 2 different kinds of engines, 4 strokes and 2 strokes... 2 strokes are very noisy in any size.

Generally 2 things influence how loud a motorcycle engine is for a 4 stroke:
A. Size of Engine
B. Number of pistons (cylinders) in the engine

A loud engine would be: A big engine with a low amount (1 or 2) cylinders. That's why cruisers (2 cylinder, big engine) are louder than sportbikes (4 cylinder, smaller engine) for example.

Generally two things influence how loud an exhaust is:
C. Construction (inside and outside) and Flow of Exhaust Gases on the inside
D. Purpose or Intended Function (racing, cruising, off road, Original Equipment)

This sounds complex but it isn't. Generally the more restricted and closer to the Original Manufactures Exhaust it is the quieter it will be. Very few aftermarket exhausts are quieter than the original exhaust that came with the motorcycle. On the other side of the coin, a free flowing aftermarket exhaust is very loud.

Now our Formula:

When you combine engine and exhaust that's how you get little or lots of noise.

For a quiet motorcycle look for:
Less of A, More of B and make sure the original exhaust is on the bike and in great shape.

For a loud motorcycle look for:
More of A, Less of B and get an after market exhaust or a poor condition (on the inside) original exhaust.

As a side note: If is much more of a challenge to make a quiet motorcycle than a loud motorcycle.

If you want a quiet bike make sure the exhaust is in great shape on the inside and outside. That all the sound baffles are intact inside and there are no holes on the outside. It also helps to look at a multi-cylinder bike with a smaller size engine.