yes here in CA, we have to have catalytic converters. I'm probably going to loose mine when i'm turbo'd. Since my car is totally illegal I have to go out of state to register it, and that state probaly won't require a cat. They're not really necessary with lpg.

That being said in a state where they are required they have gotten good at making ones that flow well and if your car is tuned right then it won't be getting hot.

So It's not a big deal really.

mine's 2.5" through the cat too, so no losses in there really.