Moose Torque Spacer
I put one on my RMX, it adds slightly more low end, barely noticable at least on the RMX which is already pretty torquey ( mine has a Stealy flywheel weight).
It won't hurt any thing, only about $20, might be different on a KDX, I did it out of curiousity. Some comments: the gaskets aren't even close, very oversized you will need to trim them down some. Also the intake sounds different at first, kinda catches you off guard, wouldn't think that it would sound any different but it's only noticeable when you first put it on, I guess you just get used to it. No jetting changes were made or necessary.