vBulletin Options > vBulletin Options > Message Searching Options (vBulletin Internal Search)
Words to be Included Despite Character Limit
If there are special words that are important for your forum but are outside the word length limits you specified above, you may enter them here so that they will be included in the search index.
For example, a web-programming forum with a minimum word length of 4 characters might want to include 'PHP' in the search index, even though the word is only 3 characters long.
Separate each word with a space.
Search Index Maximum Word Length
Enter the maximum word length that the search engine is to index. The larger this number is, the larger your search index, and conversely your database is going to be.
Allow Search Wild Cards (yes/no)
Allow users to use a star (*) in searches to match partial words? (Eg: 'bu*' matches 'building' and '*bu*' matches 'vBulletin').