whatever you have it tuned for . I had mine tuned for 19lbs. I am sure you could get 22-25lbs out of it but it would be pushing the limits of this turbo. If you have an sti I would not recommend this turbo at all. Get something bigger like an 18G or 20G. Here is a compilation I put together a while back about all the IHI turbos if you wanted to thumb through em. Again none of them are ideal to go to from a vf39 IMO. http://www.wrxatlanta.com/forums/showthread.php?t=12330 Hope this helps
Even an 18g is pushing it on a 2.5L. It just runs out of breath after 5500 rpms and falls on it's face. 20g is the minimum I would go with a 2.5L (whether it's a WRX, LGT, Baja, Forester, or STi).