Lets Fly wrote:
whats the difference from IO and O engines?

As someone else has already explained, fuel-injection vs. carburetion.

You might be interested in the information at http://www.prime-mover.org/
There's a lot of basic engine information there. Under the Lycoming section,
look for the "key reprints" in particular. I think the answer to your question
is in there somewhere, among many other things.

Dave