You can't really dyno the effects of an intercooler for a variety of reasons.
The main reason is the fact that the design of an intercooler can effect boost levels. Any modification which effects boost, will show a gain not from the mod itself, but from any changes in the boost pressure of the vehicle.
It is incredibly easy for any manufacturer to show large horsepower gains from a dyno with an intercooler swap, just by fiddling a tiny bit. If you ever see a manufacturer post an actual dyno of "before/after" IC results, also ask for an A/F and boost graph. More often then not, you'll see these are out of wack from stock, and thats where the gains are coming from.
Thats why you will generally not see a dyno of an intercooler but a "supporting horsepower" #. This is to help you decide on sizing without doing alot of research. You can get into some crazy long arguments over sizing, so I won't dive into that now, unless someone wants me to repost the mazdaspeed6 intercooler sticky from 6club. (Short summary: Bigger isn't necessarily better, and can be far far worse then stock).
Judge an intercooler by it's endtank design, its efficency rating, and its pressure drop. Not by its size, bling factor, or dyno.
This is what an intercooler "dyno" looks like.
http://www.cp-e.com/imgs/MazdaSPEED6_Intercooler_Research_PDF.pdf
Remember that the primary function of an intercooler is to reduce charge temperatures due to the compression of air molecules from the turbo. It's not designed to make power. That's merely a side effect by lowering charge temps.
Quote from intercooler article
"he function of an intercooler is to reduce the amount of heat generated by the compression of air by the turbocharger. It does this by passing the charge temp air through a series of channels/vanes which are externally cooled by either ambient air or water. The primary reason for reducing the charge temp is to help reduce the chance of detonation. Excessively high charge temps can increase the chance that the air/fuel mixture will combust spontaneously outside of the main flame front. Detonation is insanely bad, it causes excessive stress to drivetrain components. Secondary benefits include, cooler air is denser, and contains more oxygen per cubic inch then warmer less dense air. The more oxygen you can fit in a given space, the more fuel you can add to it, and thus the larger the resulting boom. (Hopefully a controlled one). )
Formula's below for those who like math. Intercoolers are measured by efficiency, which is basically the % of heat they can remove from the charge temp (caused by the turbo compressing the air) , prior to the air entering the engine. The higher the efficiency, the greater the temperature drop. Of course the problem with efficiency (and why it isn't stellar on stock cars) comes down to design. The more efficient an intercooler is, generally the larger the pressure drop of the air traveling through the intercooler. The denser the intercooler is, the more pressure loss. It is this balance of pressure loss vs efficiency that drives intercooler design."