unless a bike is geared extremely low, top speed is very good test for peak horse power.

On a given day, same rider, same road, same EVERYTHING, quickly change between old vs new part and do few flat-out top speed tests. Average the results ans compare old vs new. You need to use GPS to get objective speed number of a reasonable resolution.

Any increase in peak HP will show up as increased top speed.

Not as good as real dyno but way way better than "it feels like it has more aggressive personality" butt-dyno results.

A friend of mine used to have an FZR1000 and he worked on that bike a lot. Any change or doubt about "it doesn't seem to run fine" was tested with top speed run.
Any engine issue like valves getting out of spec, dirty air filter, chain going bad.... would always show up as drop in top speed. Just pick an empty road! Especially if testing an FZR1000

--
Mikko

 

I actually have access to a dyno.
I just don't have the time, or interest in doing it.
Too many other things on the go.
I hear you on the butt dyno. It's so subjective, that increases, and decreases in power can be misconstrued based on where they occur in the powerband.
This bike is faster, though