hi, if anyone can suggest a good exhaust i would appreciate it, i am assuming there is a leak cause i am getting a nice coat of black soot a day, or 2 after washing, and my car feels weaker than before, it is an 2000 a6 4.2, 120k miles, i love my car and it still runs good. also was considering some other upgrades, chip, supercharger, etc... if anyone could suggest the best products for the job, that would be great as well, i would love to end up beating a rs6 (might be asking/costing too much), but i can't lose to a s4 again, my heart can't handle it