As you may have discovered, in spite of its phenomenal performance as a blogging platform/CMS, WordPress falls woefully short in the search engine department. There are of course certain plugins available that will improve your search results, but for those of you who don’t want to install 15 of them to just barely imitate the functionality of modern search engines, there is another option. In this tutorial we are going to show you how to replace WordPress built in search with Google custom search.
Link: WP Beginner