the PAIR valve pumps air into the exhaust flow to trick the emissions testers into thinking that the stock map is more lean than it actually is. also, it supposedly helps burn unburnt fuels. as you know, you want your headers to remain as hot as possible and some people have claimed that the PAIR causes the headers to cool down too much as the air that's pumped into the header by the PAIR is relatively cool. most have agreed that there is no impact on performance with or without the PAIR. the main reason people remove it is because it saves about a pound of weight and makes tuning easier. it also takes all those tubes and crap out of that already-packed area which eases things like checking valves, etc...I still have the PAIR valve on my track bike and I need a new tune. What does the valve do? Let the air from the motor breathe into the air filter. I know that's just an emmisions thing, old cars never did that.
I guess if that's what is does, Removing it keeps hot oily air from entering your intake?
Thanks Doc. I might as well rip that thing out before my new tune.