Originally Posted by superman22x
Removing the Cats will net you some gas mileage, but it's also highly illegal for vehicles 96 and up. Best thing to do is remove rolling mass.
Removing the catalytic converters for any year is highly illegal. OBDII just makes it harder to get away with it since everything is computerized.
The best way to gain mileage and performance is to lose dead weight. Interior trim, seats, headliners etc. I would say the spare, but it would be a dumb idea if you're daily driving the car.