[WirelessGigabit]

Emission standards require you to maintain the car as it was sold to you.

So with DEF that means that since the car was sold with a DEF injection mechanism the car's computer will not allow the car to drive once you're out of DEF, as that will bump up the emissions.

As far as I know it kill performance, but you'll wanna have a spare bottle at the ready.

Catalytic converters on the other hand are much more impactful. They definitely reduce performance. And if you run rich you'll wear it out. So people cut them out.

California should massively increase their checks. Like pull people over for loud pipes. That would help a lot.

But you know, those people go to the smog shops that are open after working hours. And guess what, CA's government only checks them during working hours...

[maxerickson]

Catalytic converters are not really impacting performance most of the time, at least in terms of power. There are some efficiency losses from the restriction, but the net result is much cleaner exhaust. At peak power there is some reduction due to the converter, but it has been completely swamped by improvements in power density, so it isn't something anybody should be worried about. If you aren't running at peak power, the losses don't really matter.