I do disagree with my old chum Daz in one thing . The 1600 Bird still blows the pants off the America in every respect including power and is a good upgrade.
Well, maybe i was being a bit harsh. But i will say that compared to my speedy with pipes filter and airbox mods (box was still there, just opened up a but) my 1600 wasn't about to blow it away. In fact, when riding home on the freeway on the 1600 when i took delivery i was disappointed in that the passing power felt no better than my speedmaster....maybe not even quite as good ! Of course break in (which maxed out around 4000 miles) helped and by then it was a bit better. But there wasn't a lot of difference till i put tors on. Of course like i said, that was with my speedmaster being modded and having about 6-8 HP more than stock. Also consider todays americas and speedys are EFI a have more stock power than mine had. (got one as a loaner so i know that) Comparing stock to stock tho you're close to right. Not sure i'd say "blows it away" tho. For one thing the Tbird is geared a lot higher. If geared the same then it would no doubt blow the america/speedys away badly. But they are cranking about 4000 RPMs at 70 while at 4000 RPMs the Tbird is doing 105 !