I'm not super familiar with the exhaust layout on the LS. But when I start mine up there is a rattling noise (almost sounds like the car is scraping) its emanating from the center exhaust component. It comes after the headers and before the secondary mufflers. Basically dead center in the exhaust chain. What Im trying to figure out is. Is it a catalytic converter or just the resonator? I plan on redoing my exhaust soon But i was wondering if I need it for smog or not if it's a cat.
You definately need a cat for smog test. the rattle is either a heat sheild above your cat or th heat sheild on your cat. get under your car and with a glove or rag so you don't burn your hand. press on the suspect with the car running. If it stops then there it is. If it doesnt, then shut off the car and bang on your cat. do you hear a rattle?
its like this in the photo. if you start from the tips and go away from the light source. its the last muffler-like part. Ive seen people just put x pipes here so i was wondering if thats the cat or resonator.
California cars came with center cats on the early 90-94 cars. There are many non-CA cars in CA so location is not the issue it is the original market that the vehicle was certified for. The catalyst has an offset inlet and outlet. The picture you posted is AFAIK a resonator. If yours looks like the one in the pic you posted you should have a resonator.
Either way you will also have 2 catalysts bolted one to each manifold near the engine with 3 bolt flanges. I am NOT certain if CARB testing checks original vehicle market data and then checks if there is a 3rd catalyst or not. You are PROBABLY safe replacing a 3rd cat with a straight pipe or resonator or X or Y pipe. You may want to do some searching on the law.
Here is a pic of an early LS400 Y pipe that you can just see the front of the 3rd cat and make out the offset inlet. The cat is diamond shape on the left of the pic with the passenger side manifold catalyst to the right of the pic.