I live in the Denver metro area and I have to test my truck every 2 years on a dyno for emmisions. In smaller towns its not profitable to set up a dyno for a few thousand people, and its not fair to make them drive 5 hours to get tested.So, no testing for them. If you live where the majority of the people do in Colorado then the testing is very strict.The year of car will dictate what test you get. Before 1980= tailpipe test. After 1980= dyno test.

 

tacomanator, you don't think a free flow system would pass denver emissions?

 

A truck with a free flowing cat would probally pass emissions just fine as long as the vehicle is in tune.