Performance will not change. All you're doing is stopping the injection of air into the exhaust port/header.

 

It doesnt have that little hesitation if you blip the throttle.... I have ****ZERO***** popping and no backfireing either. I hadnt rode it since last summer... so when I took it down the road it still scares the sh#t out of me the first time I rip it open and the front wheel comes up in 2nd.... So I would say if effected the less than 2K rpms but no bearing above it. It idle much better and has a deeper tone while idling
But I used to pop all the time ... WAaaaAAAaP (Bang) VaRRrRoooOMM (bang) it was really bad if I engine broke

 

K, that little hesitation you were talking about when you blip open the throttle would be nice to get rid of so that is probably another good reason to do it. So was the pair valve just something to help with emissions?

Lol, I must not have grabbed too much throttle when I rode it today cause the front end didn't even start to get light, but your saying power wheelies in second without even clutching? I knew the bike was impressive but damn.

 

I weigh 170lbs, If I snap the throttle anytime above 4K in 2nd it will come all the way up to where I back off the throttle, I have never ripped the clutch on it

 

My exhaust pipe seems to be a million degrees before just after a 15min ride, I could feel the heat though leather pants from a foot away, but the Temp gauge was always less than 1/2