What are the specifications of the General Electric J85 engine compressor?
That's probably going to be beyond the scope of most on this board.  If you really want an answer to this, I'd contact Thornton Aircraft Company in Van Nuys, CA (http://www.thorntonaircraft.com).  They deal in sales and maintenance on old T-38s and F-5s as well as do type ratings in the jets.  They are intimately familiar with the J-85 power plant and could probably supply you with that info.