gains

So I've been eyeballing exhausts and so far I like the looks and sound of the Marks performance 4-2 the best. It has a nice deep rumble and it doesn't seem deafening from what I've seen on the videos of it. What can I expect in terms of performance gains from these? How do they stack up...

Having re-wired my handlebars-mounted fan switch via a relay to actually manually disable the cooling fan, I rode my usual 90-miles I-4 commute, at my usually cruising speeds of 75-95mph. I decided to leave the fan switched off, since I figured that at highway speed, there should be enough...

Is this a mod worth doing? I have a '99 with Supertrapp exhaust and stay pretty much at sea level. If it is worth doing how much horsepoer can be gained? NOTE - I understand you do NOT want to drill slides, change springs, or change air jets (unless you get a stumble).