I have a friend with a Civic. This friend is a little blonde when it comes to cars so I'm kind of used to this abnormal stuff , but this bothers me. We just got done putting an exhaust system on her car and took it for a test drive. While out on this test drive she thought it would be fun to "downshift" while going 70 on the interstate. So, she puts the tranny from (D) down to (3). The car slows down with a jerk and we can hear the exhaust doing the little downshift backfire thing. Well she thinks this sounds cool so as we are pulling off the interstate she does it again then goes down to (2) on the exit ramp. This whole time I am telling her it is not good for the car. but she isnt listening to me. I just really want to know how bad it is for the car and how long will it be before she breaks something.