Would like to know the pros/cons of both. Also I think I've heard roots is an all rpm booster and cent. has to be spooled up like a turbo. Is this so?

here is a good place to start:

SEARCH (http://www.chevelles.com/cgi-bin/forum/ultimatebb.cgi/ubb/search/search_forum/4.html)

a search on roots brings up some good info.

best place too find out about this is down at the bookstore. Look for Corky Bell's "Supercharged." It goes into the specifics of each blower. A roots blower is much less efficient then a centrifical blower. Probably around 55% at most, where as centrificals can approach 75% efficiency. Centrifical are also easier to intercool. This means more boost potential.