I bolted the Skunk2 onto a D15B1, and the motor doesn't have anything internal done to it yet. I'm on my way there soon enough. I certainly didn't lose any power, but I can't say for sure I gained any. The top end seems to have a little more oomph. I used to stop making any power at about 6,500-6,600. Now it keeps pulling a bit longer. But remember, we're talking the wimpy D15B1 cam, and, what, about 9.2:1 compression.
The motor has the Skunk2 IM, T1R 4-2-1 header, Hondata S200, 2 1/2" mandrel exhaust, 58mm TB, and 3" cold air intake. Next I'll be bolting on a head that has been shaved .050", and running with 1 layer of a D16Y8 HG, so compression should jump up to about 11.5:1. At the same time, I'm throwing in a Colt Cams D16A6 regrind. We'll see where that gets me.
Next, to put good use to all these high end parts, I'll be building a D16A6 block with a D16Z6 head, and lots done to the inside.
So to answer your question, I believe I got some gains from the Skunk2 IM, but don't have any hard facts to back it up. It however was a bitch to install. The firewall clearance is "minimal" to say the least. I had to ensure the IAC was bolted on before installing the IM, as there was not room to do it afterwards. I had to cut the head of the bottom IAC bolt down to half its original height. I had to give the firewall a few good whacks with the BFH to gain the required clearance. Keep in mind that I am also running the Hondata IM gasket, but that only accounts for about 3/32" less clearance.
The only other problem I had, which will affect any of you planning on using this IM was to do with that coolant hose neck. The clearance between the neck and the runner for port #4 is so small, that the hose would not squeeze through the gap. I had to cut the outside diameter of the hose down in half for it to slide in. I also had to use a regular screw type hose clamp, as the Honda one is thicker steel, and would not fit.