I was wondering would it be worth to get a full cat back? I have a muffler on there now. will it make much of a diffrence?

 

No. The exhaust on the Neon's are optimally sized from the factory and they are already mandrel bent, so going with a larger exhaust will actually hurt your performance, but it would make it have a deeper tone. However, if your Neon is modified enough then a larger exhaust would be needed and would improve performance. If your looking to get a stock style exhaust that is made from better material like SS, then that would be a good idea as well. Your best bet is to stick with a good muffler and a header, possibly even a high flow cat, but going larger or eliminating the cat completely will slow you down and make it louder.