318 exhaust size

Something I knew upfront got confirmed as an eye-opening experience on the dyno tonight.
Stockish 318s with 2.5 dual exhausts leave power on the table.

It had stock castiron manifolds with dual 2-1/4" seperate exhausts into turbo muffler like mufflers and tailpipes.
Now there's a pair of full length Doug's headers, 2.5" dual exhaust, X-pipe, Borla ProXS mufflers and tailpipes. This setup makes 20 (!) ft/lbs less @ mid range and about 8hp less at WOT.