WoooHoooo, here we go again...

Do they work? Depends who you ask. Some swear they do, most say they do not.

Even if they do work, which I'm personally skeptical about, it will add an extra level of complexity that these engines do not need.

For my money I'd just go ahead and get a bigger/more powerful engine and be done with it.

If you do a search you'll find tons of threads on this as they crop up every week or so.