I am looking to buy the Flowmaster Delta Flow 50 series exhaust, SI/DO. But I am not sure to go with the "Offset In" or "Center in". What is the difference? What would be recomend?

I have a F150 2003 Flareside 5.4L

 

i always thought offset on a muffler was determined by how the system fits up under ur ride. Meaning get whatever offset or center best matches the bends of your piping so it bolts straight up. Doesnt really matter as far as sound or performance.