Cat's really don't make much difference unless you're running lots of boost. Then the restriction shows a little, but only costs you maybe 10 hp. Honestly a small price to pay: #1 to avoid a ticket. #2 keep the air a little cleaner for our kids. I got pulled into one of those a while back, and they kept me and my 2 year old there for almost an hour. In the end, no tickets because my car is set up to autocross as well as drag, so it's only .5" lower than stock. They didn't even notice. Also only 15" rims, no huge spoiler, and full exhaust. Fortunately my car never had a cat, and never has to be e-tested. 1984 Rabbit to old. They spent twenty minutes uder the car trying to find holes in the floor to. But the car only has 90,000 kms on it. Just turned 90 last weekend. So after an hour, they had nothing on me and I was allowed to take my son to the park, which is where we were headed when they pulled me over. Not even speeding.