I bought a set to play with. Xied's
Installed them on a 2007 Road glide with 16,000 miles on it. The bike is stock and has always run fine.
Install took all of ten minutes.
The bike runs well with them.
Throttle responce is a bit stronger.
Bike sounds a little deeper.
Roll on from 60 in sixth gear is stronger.
As for heat I tested these over two weeks on rides I make alot. I used a thermal gun and took temps in 6 places. I ran the bike with and with out the Xieds many times on the same runs and conditions.
while at times they did lower the temps a small amount it was never over 20 degrees and temps did work thier way back up if the bike was left sitting. However they did appear to slow the heat rise a bit.
They did cost me a small amount of fuel milage.
Over all they do just what Nightrider claims for me. They do NOT reach some of the out landish claim I have seen posted about them.
And heres some food for thought I decide to check temps on my 96 Fatboy with a stage 1 done to it come to find out they are not much different than the 07 ?
With that in mind last weekend at Lacrosse WI there were a lot of motorcycles at the S&S party

.
I did random checks of engine temps of all kind of bikes that were riding together.
There was every mod and trick you can image there. Seems none of the temps veryed that much.
I have found that many using a thermal gun are some what fooling them selfs.
It is very improtant that the gun be pointed at the same spot same angle and same distance everytime to get a true reading to compare. And not on crome.
While playing with mine just a hair differnce in some spots made a 40 to 50 degree difference. To get true readings I made two rods taped to gun to hold angle and distance and marked each spot.