Primary size and length on SC engine

Example; if you exhaust port was perfectly square and measured 2" x 2" that means the primary inside diameter must be 4 square inches or greater, and the collector I.D. must be 16 square inches or greater, no matter what the length. The formula's for measuring oval's and round tubing can be a little tricky. You can measure completely around a odd shaped opening and use that as a circumfrance in a circle, square inch formula.