Afaik they block off where air gets recycled for combustion and stops the pops or bangs from exhausts on over run Iv never fitted them to any of my bikes tho
Here is a full explanation of what they do. Graves Garage-Why use Smog Block off Plates? What do they do? - Sportbikes.net
The PAIR system can be disabled without going to all the trouble of removing it and fitting block off plates. Now I havent fully explored this on the blade, but on most bikes there is a PAIR solenoid which is and electrically operated valve controlled by the ECU which under certain conditions allows air to pass through it and via the PAIR system into the exhaust ports, and simply unplugging this will stop its operation and allow no air. If you want to go one step further, putting a marble or ball bearing in the hose between the airbox and PAIR solenoid will also disable it. One step further again is remove the PAIR solenoid and hoses and blank off the PAIR valves with plastic caps. The final step is remove the lot and fit the block off plates as described. Be aware that any of this is probably illegal, but so are most pipes. I did all of this to my VFR, and one immediately noticeable effect was that the exhaust was quieter at idle because the PAIR system was not pumping air into the exhaust and burning unburned fuel in there which was adding to exhaust noise. I probably will do this soon to the blade, when I work out where everything is, because the exhaust (R77) is bloody loud at idle.
You have to block the pipe or the intakes on the blade, unplugging It doesn't stop it sucking air in.I Wanted it as the pipe needs blocked For a custom dyno map/fitting PC autotune or the readings will be wrong. They sometimes just clamp the hose but I want to do away with It altogether. I'll take them if you can hang on until my payday
