I'm in the process of looking/installing a 4" on my truck. I have to install the muffler. Here in MA they check everything. I could get a sticker by other means but where my trucks are all registered and insured as commercial vehicles I'm not going to chance it when the dot decides to do their checks, and these seem to be more frequent!

 

A turbocharger is considered a muffling device in some states.

 

No kidding. My neighbor is a Sgt. with the MA State Police. He gave me the # for the commercial truck division. I'll call them tommorow and see what they say. I'll post back with the answer.

 

No kidding. Learn something new everyday. Now I know why both my truck and motor home are fairly quiet without mufflers. I always wondered why they were so much so than gasoline engines.