Actually, there are two search features. The search at the top of the forum (main index) is a generic search. Like mentioned, you can add advanced searches.
The other search is local to the sub-forum that you are in. For example, click on the two-stroke engine sub-forum. Then, you will see a "search this forum" in the sub-forum header.
EDIT:
Jeff is faster than me and my post is redundant. I will attach a pic for the 2 searches.