Rep Power: 424

Does anyone know how much vertical travel the suspension needs? I need to know because I can only lower my car to a point where the suspension can bottom out and still not rub on the tires. The rims/tires stick out under the fender lips in both the front and back so if I go to far, I'll have problems all around. I'm thinking with something like an H&R or Sportline drop I should still be ok, but if anyone knows just how much clearance I need, you'd make me very happy.