Hi WEZ, the answer relies on your answer ! Is your bike EFI or Carburetors ? I know from dyno tuning my EFI 09' America that they are tuned very rich @ high rpms and run very lean everywhere else, so a retune would be advised for EFI,carburetor mightn't be so compulsory, as induction and carburetor response to freer flowing exhaust would still meter the fuel to match intake/induction volume increase, but still wouldn't be ideal best/max out put !