Supertrap Megaphone

Wondering if a single Supertrap megaphone with a closed end cap would be able to flow good enough to not create additional restriction? This of course would be run straight through, eliminating the cat box and all its weight. Ive found that they can be purchased as a universal fit 17.5 inch megaphone with either a 1.75" or 2.00" inlet. Can someone tell me the factory outlets outside diameter?

I would have thaught that someone would have answered up on this