Yep.
Exhaust valves allow an engine builder to raise the port timing quite a bit, creating more top end hp, while providing a nice punchy low speed performance.
Power valves, while some folks might call exhaust valves by that term, can be found inside a Holley carbeurator.
Next time you're next to a Skidoo, pop the hood and look at the cylinders above the exhaust manifold, red cap onthose. Yamaha's are computer controlled, but in the same location.