If you do a search on exhausts through the search engine for this site, you'll get lots of info. It is an often discussed topic here.
I too like the dual exhaust set up on the Hayabusa. Most of the time that means a slip on set of cans. Yoshimura, Two Bros Racing, Akrapovic, Micron, Muzzys, and a multitude of other manufacturers all make slip-on / bolt-on sets for the Busa. You can get them in aluminum, stainless steel, carbon fiber, and some come in colored finishes (like Micron). You can expect to pay between $400 and $700 depending on the maker, materials, and seller.
I have Yoshimura bolt-ons. They are very well made and when installed angle the exhausts inward at the rear. Gives the bike a more narrow appearance from the rear. I think most others do the same thing. Yoshimura slip-ons are oval. Some other makes are round, some larger, some smaller -- there is some variation in style out there.
Slip-on exhausts are all going to be similarly loud. Since the stock header pipes are kept, there won't be huge variations in the noise they make. One exception is the Zyclone baffle Yoshimura exhausts, which are louder than stock, but not as loud as the other slip-ons. Power gains with a slip-on system won't amount to much regardless of what the manufacturers claim. They are for better sound and appearance -- not for power.
A full system will replace the header pipes, mid pipes, and exhaust cans. They can be 4 pipes into 2 pipes into 1 canister (4-2-1) or 4 pipes into 2 pipes into 2 canisters (4-2). The latter can also be 4-2-1-2 depending on the way the pipes are plumbed together. With both 4-2 and 4-2-1-2 you end up with a dual system.
HMF makes a couple of dual full sysems for the Busa. One is a standard mount that puts the exhausts exits near the stock locations. The other is a high mount that puts the exhausts cans up near the rear seat. HMF Two Bros Racing also makes a dual full system. So does D&D.
These full systems are where you can pick up some additional power. With a good map programmed into a Power Commander, these full systems can add 10 HP (or more) to the bike. They also weigh much less than the stock exhaust system.
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