i dont know what it's called, but it's to reduce the sound of the motorcycle manually, and when you want it to get loud you can control it manually.

Commonly called an "exhaust cut-out".

It's a simple Y valve, usually cable operated.

Jay may have had the incorrect term, but the definition is right.

It dumps the exhaust to atmosphere before it gets to the muffler (aka silencer).

Illegal for road use in most places.

It's called an Exhaust Dump Valve

When you open it, it dumps the exhaust flow out before the muffler but routes the exhaust through the rest of the exhaust system while it is closed.

What you're referring to is an exhaust silencer.

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