I am looking on line at local ones for sale and the ads are saying anywhere from 318-330hp. I did some research on line and sites are saying 250hp. Is this correct? Or are people just making up hp numbers for there stock S4's?

It's about 225-240 at the wheels, and about 275 at the crank. Check out www.audiworld.com. It's a free public forum, and there is a ton of knowledge there.

The first S4 came with a V6 twin turbo, the same engine used in some models of A6, with 250 hp. They change the motor on more recent versions using a 4.2 litters V8.
What you found is correct.