I have long tube headers, off road y pipe, and a flowmaster 40 series muffler. How much difference would it make if I just reduced the pipe behind the y pipe to the stock mid pipe, as compared to having a shop put in 3 inch. I think my muffler is 2.5 inch inlet anyway.

 

it makes a difference but if you cant afford the cat back yet its not going to hurt anything.

 

I can afford the cat back, I was just wondering if it makes enough difference for the money. But I decided to just do it now instead of putting it off.