Exhaust pipe size

Does anybody have any dyno experince with this? 2.5" Duals seem a bit large but I am just guessing. from 4/6 cyl experiance you can see a big loss on an exhaust with an exhaust that is too large. On the Rally car we saw a 14 horse loss with a 2.5" exhaust 232hp @ 9000 vs 218 @ 9000 at the wheels this is on a 2.0L 16v DOHC BIG individual Trottle Body intake two injectors per cyl. Move a Lot of air any ways in theory the 2.5 was going to help on the top but didnt produce.