Warranty is at risk for sure, but thats with any engine modification of course. There is a dealer mechanic on this board that will help you with that, but you have to be in Southern California for him to help.
Performance gains are only noticed when you get a tune that knows about the DP. Otherwise low performance gains felt in the midrange to top end. Don't don't without a tune to address the DP. The gas smell is not worth trade off if the power gains aren't achieved.
I have not gone to smog yet, but it's possible to pass with proper coding on a tune. I'll be the first to try it in March of next year. I'll let you know
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