The basic job of an intercooler is to reduce the temperature of the inlet air, which is usually quite high due to the compressor. One of the theories of gases states that as pressure rises so does temperature, along with creating higher pressure the turbocharger's compressor also increase the temperature of the inlet air dramatically. Sustained high boost can rocket up the intake charge temperature; stock boost settles at ~110'F, running 12psi jumps that number up to 280'F+!!(Tested at 70'F ambient) High inlet temperatures can cause severe detonation.
There are two main types of intercoolers, air-to-air, and air-to-water. An air-to-air intercooler uses a big, efficient 'air radiator' that cools down the intake charge by using cooler outside air; an air-to-water intercooler uses water in place of air to do the cooling, and cools the water with a radiator. Air-to-air systems tend to be simpler and weigh less, but air-to-water I/C are more efficient, and have a smaller pressure drop.The efficiency is defined as the ratio of the temperature removed from the air charge by the intercooler relative to how much temperature is put into the charge by the turbo/supercharger. Testing for efficiency rating. If the turbo/supercharger puts 150 degrees F into the charge when compressing the air, and the intercooler removes 110 of those degrees, then the efficiency is: Eff = 110 / 150 = .733, or 73.3% Accounting for pressure drop. For good solid performance, the pressure loss across the intercooler ought to be kept to less than 1.0 to 1.5 psi. If any pressure in excess of 4 psi is measured, then the intercooler is not suited for the job and certainly harming the performance. Using FMIC set up 
Blue is the cool air being pulled in from the Intercooler. 
Here's a look inside the stock Intercoolers
All the aftermarket side mount Intercoolers will handle most all the turbo's out there for the Z32. If you look at core size's. You'll see the size's are just about the same size as the most marketed FMIC.
All Greddy Intercoolers are designed to give maximum cooling capacity while allowing for minimal pressure drops. This is achieved by properly sizing the core and tuning the internal core with either a V-spec. core or with a different inner fin pattern in the R-spec core. Are said to have a 75% efficiency, with 1psi pressure drop.
Greddy FMIC 294mm x 600mm x 76mm ( 2 row )
Greddy FMIC 294mm x 600mm x 115mm ( 3 row )
Greddy SMIC 195mm x 155mm x 100mm ( x2 )
Greddy SMIC 
HKS Intercoolers utilizes an application specific tube and fin intercooler core with cast aluminum endtanks, as well as mandrel bent intercooler pipes and silicone joint hoses. Are said to have around 70% efficiency, with 1.5psi pressure drop.
HKS SMIC 200 x 259 x 65mm (x2)
HKS FMIC 400 x 255 x 65mm You can see the two intercoolers here just welded together with the same size cores as the side mounts. Which to me doesn't make sense at all why it cost twice as much.
 
Border FMIC 600mm x 300mm x 76mm 
Apollo 
Stillen SMIC 238mm x 213mm x 89 ( x 2 )
Stillen intercoolers have a core that is manufactured by the well known racing company called Spearco. They are a dedicated intercooler manufacturing company. Very large, very efficient Air/Air I/C, stainless/steel piping with around 80% efficiency and less than 1psi pressure drop. They are listed as having a surface area 35% larger than stock and also stated has being the biggest SMIC replace on the market. One can clearly see by this picture.
Next to a stock IC 
Here's Video of Mike K's SCC Project Z with over 650Hp dynoing his car using Stillen IC's [ http://www.vq30de.net/stillen_oct2002/dscf4607.avi ] 
I suggest if you do go the FMIC way, get a vent panel like Mikes here. This will allow the radiator to receive more air because the FMIC has block the direct flow in front of it. 
Here's a look for a size comparison of most of the brands. Greddy SMIC on the left, stock up front, Stillen SMIC behind it, HKS FMIC on top, Shop marketed FMIC back bottom. 
The 1990 300ZXTT had inner fender liner louvers for the first few months of production, but they were deleted as a cost saving measure. Unfortunately, they no longer exist in the Nissan parts system anymore, so if you want them, you have to do it yourself. These significantly improve airflow by giving the air a low-pressure zone to migrate to. 
Please anybody add to this post :)
 STAGE V++++
Going to XV+ and beyond :) Yellow Z STAGE II
Going to XI+ |
The Intercooler post - 
