Engines, to me, are one of the most interesting parts of control-line
flying. They are very important in any class. There are racing engines
that scream because they have such a high rpm and there are aerobatic engines
that spin slower but still have alot of power. If you have a bad engine
and you try to do a wing over then you may lose line tension and in turn
lose control, and crash. And when you have a large aerobatic aircraft that
may have taken months to finish, believe me you don't want to destroy it.
So you can see engines are very very very important.
Here are some engine reviews click on the appropriate make: