I live in CA, been riding out here for a long time.
I upgraded my performance with the 2into1 thunder header from HD.
I have been next to the Police at lights down in the beach areas (this is where the bad stories happen) with no problems. I have seen guys pulled over, and ticketed for loud pipes but they were straight pipes and the cops aint stupid out here, they know upgrades from the straight pipes.
My sound level doubled with my upgrade, not the loudest but loud none the less. I've yet to get any negative attention from law enforcement.
Ride safe and smart and you should have a great trip here in CA.
You're more likely to get stopped for your tunes being too loud. Give us guys out here a heads up when you make the trip and you might just get a tour guide.
BTW- welcome to the forum!!