I currently have a full 3" mandrel bent ATS exhaust on my IDI. I am getting my 5" stacks installed on the 16th. I was just gonna have an elbow with a 3" to 4" adapter and then a 4" to 5" in the bed. Would it be beneficial to have the rest of the undercab pipe replaced with 4" tubing? I imagine I would have to retain the 3" down pipe though.

 

it might help lower the egts

 

It would definately help with EGTS. It would probably sound better too!