In regards to what CHISO9QP posted earlier (quoted below). I have a Quattroporte-S in the final model year (MY 2013, but really left over 2012) and my car does not have valves at the mufflers. The only Quattrportes that had valves are the 2009 and later Sport-GTS. If this is wrong please let me know.....
".....I just had it confirmed today by Maserati that in the later S models (4.7 auto), the valves do indeed open at 3,000 revs when sport mode is active. There appeared to be a bit of debate about this! I believe that only the Stradale in race mode enables the valves to be open throughout the rev range....."