Hey everyone, I have a 2006 Mountaineer v8 and I want to build a custom exhaust system. I am at school right now but want to start designing the system now, and need to know the pipe size from where the two individual pipes meet up to the back of the vehicle. I believe it might be a 2.5 inch but can someone clarify? Also any suggestions on what to do for best fuel efficiency and power would be great!

 

Stock is the best size.