It's certainly possible. The pistons may hit the valves on their compression stroke.

As for the butterfly valves, I've always heard...

Bad things can definitely happen. First they will fall into your intake manifold. If they don't get hung up there, the next stop may be one of your cylinders where the parts that fall in will likely stay until you remove them.

Loose parts in your intake and cylinders is a recipe for disaster IMHO but then again IIWY, I'd wait to hear what some of the other more technical forum members will say. <img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" />