A later model T/A will get an automatic fail at the smog inspection station if they see you're running an earlier engine, missing your cat, EGR, or any other obvious smog equipment. But living in CA doesn't mean you can't have performance and comply with emissions too- I'm planning to use Hedman headers, which have an CARB EOD exemption no. (D-167-27) and are smog-legal. Those headers will run into a y-pipe, single cat, then another y-pipe into dual mufflers- once the inspection is over I'll have an x-pipe "test pipe" that will bolt in place of the cat section. Alot of shops charge $300-500 for the "under the table" smog cert- good money that could be applied to getting your engine to pass smog, and then you only have to pay the regular fees.
Back to topic, I agree with the others that you may have some holes in the firewall or floor pans letting exhaust into the passenger compartment.
