I have already assembled a very comprehensive page of exhaust information touching on quality & performance issues for my RC51 site. Yes the page was originally oriented towards RC51's but most of the information rings true for all brands. If you have the time or interest you can read it at the following link: Click here

& for those of you that aren't going to click the link & read what I have written, but then immediately turn around & e-mail me a question asking about Two Mothers exhaust, let me go ahead & say I think they suck.

As I stated on one of the forums "Anyone can make an exhaust system especially slip-ons, but very few companies really know how or take the time to tune the exhaust to improve scavenging & power delivery. Many companies have a one size fits all cannister & they simply bend some tubing to fit the bike & charge a small fortune for it... Sometimes they get lucky and get a really good power output sometimes the power gains are nothing more than you could get by simply removing your stock muffler"

Just to illustrate my point, this is one of my favorite examples, the following chart is a back to back comparison (same bike, same day, same dyno) of the top two premier slip-ons for the RC51. Notice the difference between the torque curves then tell me all slip-ons are created equal LOL click here to view the chart

Now here's the kicker... After saying all that to insure that you were informed of the realistic possible variances from one brand to another I'm going to turn right around & say that I firmly believe at this point that due to the design of the 919's engine that ANY slip-on is going to be beneficial to producing more low & mid-range power just by freeing up the restrictive nature of the stock exhausts & letting the engine flow as it was designed to. I truly do not think that you will see the type of problems associated with exhaust tuning on higher revving engines (i.e.dips in the power curve or stumbles at certain rpms etc...) Now top-end power may be another story, but anyone that bought this bike hoping to extract top end performance simply bought the wrong bike as the entire premise of this bikes motor with the cam phasing & very small 36mm throttle bodies (the CBR600 has 39mm throttle bodies) does not lend itself to peak power as the valves simply aren't open long enough at high revs to get sufficient fuel mixture into the cylinder for a optimal burn.

The following pics are courtesy of Matt Sargent "HondaSarge" from the yahoo 919 group