Originally Posted by MY99

I did the same after reading an article in a Top Gear Australia magazine that said something along the lines of "a remote controlled version of HSV's bi-modal exhaust would not comply with ADR." I couldn't find any reference to variable or bi-modal exhaust systems in the relevant legislation.

From a legal perspective, there is no reason to deem a variable exhaust system illegal if it complies with all regulations and standards in both the fully open and closed position. If the system wouldn't comply when fully open (eg: bypasses the muffler such as the screamer example above) then it would be illegal. That is not the case here.