Akropovic; it is the only 4 into 1 pipe for a zx9. i have had a muzzy, d&d , and now an akro. the d&d sucked. it leaked like hell , was loud, and and did not perform as well as just a slip on and a stock head pipe.The muzzy offer an increase in peak hp but sacrificed midrange and was loud.The akro offered greater peak hp, drastic midrange boost,and sounds great.the akro was a bit pricey but was worth the extra $.
I recently installed a black to green faded micron slip on to my '02 zx9r because the serpent headers aren't available for carbureted bikes, yet. Prior to that I ordered a full system from HMF Engineering with a beautiful black powder coated canister but they sent the '01 version. I have a buddy who went the "conventional" way with good old Muzzy. With the full Muzzy ti system and rejetting, he's claiming gains of 7-8 hp on the dyno. I did read the article with the Ak system adding 10 hp to the bike but unfortunately, the pipe is yet available... I checked!!! If you want to avoid a migraine, refrain from dealing with the following companies and their customer service departments: HMF Engineering, Micron, Wolf Exhausts, Boss Exhausts, Lockhart Phillips, and Quill... None of 'em have us on their "to do" list!!! I learned the hard way!
I used an Akrapovic pipe on my 2002, which in my opinion is the best choice.....(the pipe for the 2000 + 2001 model), it fits perfect.....no adjustments or other issues at all.
It's a 4-1 w/merge plate and crossover tubes.....it pulls very well out of the bottom.......no dips anywhere, after installation of a 4 degree ignition advancer and my carb kit, it made 140hp + with great low end and midrange. The top end above 9000 is awesome !!
Handlebar vibration is very low and the closed to part throttle problem is also eliminated.
Similar results can be had with a Slip-on........More midrange than a full exhaust up to 8000, but slightly less peak (2 to 4hp).
If you look at my website, the 2000 + 2001 dyno charts are nearly identical to the 2002 model.....