There are smog checks in California for newer vehicles, and yes part of that includes a visual inspection of the engine, but you can take the vehicle to a referee to get it signed off. I know a guy who has an SRT 4 that is throwing down over 400 whp with a stage 3 turbo get and some other goodies and he passes emissions just fine because when he has it tested he dials the boost controller down to zero psi.