The standard box (minus the acoustic) valve is very good. I had my car RR and remapped recently and the guy took off the airbox to see if unrestricted airflow would increase power. It did increase power....by 1bhp! Though my airbox is modded slightly, L bend samco induction pipe, 50mm and 63mm alloy hoses to replace the cr@ppy standard fabric ones and a clean standard air filter. Ok it doesn't look as flash as a Maxogen or Viper etc, but the mod only cost me the price of the alloy hoses, 20 odd quid. Oh and I have the Scorpion RS192 CATBack exhaust too. Before remap 175bhp, after remap 183bhp.