What do I need to do if I want to install a 09 ST 2into1 with 18mm oxygen sensor bungs on my 2012 with 12mm oxygen sensor bungs ?

 

pretty sure ive seen post in here on adaptors for the different bung hole size, the wires may not be long enough though. on 09 the sensors are about 3 inches from the cylinder exhaust outlet. on the 12 both are by your right floor board guessing u may have to extend the wires and dont mix up the sensors if your 12 is like the 09s there is a difference in the front and rear sensor, wont run right if you swap them

 

Won't work. The ECM is programmed to see the bungs where the bungs are located on that 12. The 09 position would drive the bike insane, quite literally. NOT kidding either.

Now... the fix would be to have someone weld in 12mm bungs at the proper points on the 09 pipe.

 

You could run a tuner that eliminates the o2 sensors if you really want that pipe.