An intercooler cools the inlet air after it's been compressed by a turbo or supercharger. This has two benefits.
There are several intercoolers from factory cars that can be made to fit in a 'front mount' position on a Gemini, such as Toyota Supra and Mazda RX7 units. The Mazda RX7 unit is quite good for moderate power applications and is one that I have installed before as shown below. As it is originally designed as a top mount intercooler, the air outlet must be cut off, and a new outlet welded to the side.
There needs to be some metal cut from the radiator support panel to allow the installation of this intercooler. The metal removed from the nose cone is more cosmetic than structural, and the cuts are covered up when refitting the front bumper bar and grill.
It is important that the metal you remove does not structurally weaken the radiator support panel, as the panel also serves to help stiffen the front structure of the car and keep the chassis rails in their correct location. This means the suspension will work optimally as well, and the car wont flex itself to death.
It took a while to make sure it looks neat. The metal I chose to remove serves two purposes. The main one was to allow the physical fitment of the unit, whilst keeping the radiator in the factory position. The second is to increase air flow through the cores of both the intercooler and radiator, which is why I took some off the front face of the nose cone. I also moved the number plate up so its on the front of the bumper bar, instead of hanging underneath it blocking flow.
The actual metal that will need to be removed with the particular intercooler you want to install will be different to what I have removed, but these are the general cuts that can be made.
The plumbing to and from the intercooler also has to go somewhere. On an intercooler such as the RX7 unit, where it is modified to have the inlet and outlet on opposite sides, there are small squarish holes in the sheet metal next to the headlights that can be opened up further. This one is larger than needed for the rubber bend alone as it feeds air to my air filter which sits behind the headlight.
There are various ways that the intercooler can be hooked up to your induction set-up, below are some photos of various combinations I've had with the same intercooler in the same location. The first is for a blow through carburetor set-up.
The photo below shows final plumbing from the intercooler to the throttle body made from 2.5" exhaust pipe using mandrel bends. I would have preferred aluminium, but aluminium mandrel bends were pricey and hard to get hold of at the time.
In an attempt to increase the efficiency of my intercooler install, I painted the cooler black and added some air guides. Black is the best colour for heat transfer, however I'm not sure if the coating of paint acts as insulation and this cancels out any benefits of the colour. The air guides are to increase the pressure immediately in front of the core, forcing more air through and increasing the cooling effect. You may notice that the guides are pointing inwards, opposite to a funnel. This is intentional, as a higher pressure level is achievable this way.