I'm with you on "perceived" improvements too kiwi.
However, the "bomb" type do give a boost,and a big time one at that. While dynos show a boost with them on the top as well, they also show...and the rider feels...a major increase in off-idle torque. It flat works.
Also, there have been many,many dyno reports not from the manufacturer that show improvemnts in power and torque,and top to bottom to boot.
I've seen them for 450X's for instance that show nearly a full horsepower (.
minimal gain top to bottom with mid-range gains in the .8-3.7 hp range,and that's not insignificant.
Some bikes are more affected than others. FMF's 4.1
slip-on for the 09450R for instance had a nearly 5(!) hp gain in the mid-range, with a slow increase in power from 8500 to rev-limiter, where stock it was totally flat,and at least .5hp weaker.
Yes, pipes are expensive, yes we don't need all the power anyway, but who cares? Most look bitchin', sound better and that's not necessarily louder either, and we do this for fun.
A good name brand exhaust system will provide a nice boost and you can feel it, as long as the jetting matches the pipe.
Also, Don Emler from FMF is an American sucess story we should all be proud of.He stayed a 'garage' guy for years, he built a great company selling American products throughout the world. If you call FMF you'll get personal service.
He has nothing to apologize for because he doesn't work out of a garage any longer. Doug