I think I need to meet up with you, Larry and have a look at your stash of side pipe material

3.5" sounds about right to me. "Big Rig" may be a little too much

1986 Dodge Ramcharger 440 2wd, Bracket Racer Under Construction
1998 Ram 2500 QuadCab, new daily driver.
2008 Honda Element
2014 Carry-On 7x14 Cargo Trailer