Sierra Design Nomad 5 What Is A Loud Californian Legal Exhuast (that Can Pass Smog)?

What is a loud californian legal exhuast (that can pass smog)? - sierra design nomad 5

Ive got one GMC Sierra 1990 V8 Chevy 350 and X-design flowmaster dual pipe ... I heard from someone that I can get an exhaust configuration that is only because of the legal works on paper, but are considered illegal, without it no one knows what silencer? Or maybe something like in this case only the examination of the contamination?