You should listen to me. No, seriously, listen to me.
Join Date: Oct 2008
Location: Santa Barbara
Motorcycle: Blue 2006 GSX-R1000
Re: K5 stock exhaust vs Suzuki Yoshimura Tri Oval
That looks like the 99000-79N12-021 catalyzed muffler. I can't tell from your pic but the label normally has "Catalyzed" between "SUZUKI" and "Tri-Oval". Other features are a permanently attached/welded on midpipe, an integral exhaust control valve, and a small water drain hole at the bottom of the front cap. The muffler was apparently included on the CRU models that were only sold in the UK in 2006, hence the catalyst which I think kept them Euro 3 compliant. They used the standard E2/E19 ECM. The muffler was well thought of but expensive. Claimed 6% more torque at low RPMs, probably due to the control valve. Search here for the PN and you'll find a bit more info/pics.
I don't recall ever seeing that muffler on a Yoshimura site, i.e. it may only have been available through Suzuki.