i've been looking for the same things..... here is a few things i found out. I'll include some links to help you out.
you can do an engine swap with a 1987 supra. right now you probably have a 5mge engine and the 87 has a 7mge (or 7mgte with the turbo). This is a little costly to do, but if you want a big performance difference thats the way i would go.
http://andy.supras.org.nz/
another way is to just turbo charge the 5mge (making it a 5mgte) It is cheaper to do it this way and easier then performing a total engine swap. If you do this it will probably get up to about the same hp as a stock 7mge engine.(i'm guessing). This is the route i will probably be going in the near furture
http://www.socalsupras.com/members/J...rboArticle.htm
and third you can do little things like short intake or something like that....or some other performance stuff like rods and pistons and stuff. here's a link that has a good amount of stuff like that, but you may find them cheaper somewhere else. this just gives you an idea for what you want:
http://www.rabidchimp.com/
if you got any other questions let us know.