765 Decat `21 Str Header

My 'Euro 5' Street Triple R landed in the states with two cats which clearly impede gas flow and hence power (one cat in the header and one in the muffler). My quest for better exhaust flow on a budget led me to decat the factory header and add a catless (Euro 4) Arrow muffler for improved flow and sound (the new Arrow was $385 USD on eBay). I also had the OEM header ceramic coated for the increased efficiency of higher flow velocity from better heat retention. The necessary air/fuel ratio adjustments are done automatically by my auto-tuning Rapid Bike Evo fuel module and the engine is now supremely happy as am I with the improved performance (better throttle response, torque and engine smoothness). These Arrow mufflers are known to be on the quiet side of the aftermarket spectrum but the de-catted engine did become a little louder and deeper sounding. For me, the virtue of these mods, in addition to low cost, is the retention of the torque-enhancing factory header crossover tube. Also, unlike straight-through mufflers which typically cause low-to-mid-range torque losses, the carefully engineered Arrow muffler does not cause such losses while producing higher flow than the factory can. ---YMMV---
Cheers from the Smoky Mountains of Tennessee...!