o2 sensor ports

Hi, just wondering should there be one port per exhaust pipe for the o2 sensors on a c800 2005? Looking at a set of V&H Cruzers but only one pipe has the o2 sensor port, shouldnt both pipes have one?
Thanks

Nevermind should have searched. There is one sensor on the bike. 
Question though, does the o2 sensor make much difference to the performance of the bike anyway?

Very very low revs, nothing more than that I am told. Best wait for some clever guys to chip in.

1 sensor from 05 to 08, 2 sensors from 09, They lean the fuel air ratio out for about the first 3rd of the throttle, you won't really notice the difference performance wise, probably less snatchy at low revs with them disabled.