But first, some background.

Uncle – as manifested by the Environmental Protection Agency – has long decreed that any modification to a street-driven car is illegal (under the Clean Air Act) if the modification entails the removal, disabling or "defeating" of any of the car's factory-installed pollution control equipment. This encompasses every car built since the very first emissions devices were installed in cars back in the mid-late 1960s.

It goes even farther than that, actually.

It's illegal to replace any factory part or system that could affect the car's emissions with an aftermarket part not approved by the EPA – even if the car's emissions aren't negatively affected.

Even if they are reduced.

This happens more than you'd think.