Originally posted by IS2Scooby
FMIC's are better on the street... Plus they have pimp-a-bility.

After 5 years of debate, others are now following ATI's leadership and the truth about the numerous benefits of intercooling is clear. And for automotive street use, air-to-air technology is always preferred over air-to-water, assuming you have space to mount the intercooler. In addition to concerns such as installation complexity, battery relocation and tuning, air-to-water intercoolers are inherently inefficient when used when used to with water alone. Air-to-water intercooler systems require a secondary heat exchanger (radiator) to cool the water, in addition to the intercooler itself. The heat created from the supercharger compressing air (Boyle's Gas Law) is first removed by the water circulating through the intercooler. This heated water must then be pumped through a radiator located in a fresh airflow stream (typically at the front of the car, where air-to-air intercoolers are mounted), and then the water is returned to a tank, into which water and/or ice is added. The overall system effectiveness is greatly "watered down" because this effectiveness is a function of the individual effectiveness of the two heat exchangers. For example, 60% (intercooler effectiveness) and 35% (radiator effectiveness) produce a system effectiveness of only 38%. This "two-step" cooling is, by design, inherently inefficient.

In my opinion, a water-fed unit is not worth the investment. The required amount of care the system would require outweighs its usefulness. It is generally more expensive, and since it often requires moving parts, more prone to failures.

Which type is better? Depends on your goal. From where I sit it seems that air-to-water intercoolers are used mainly for convenience - either to eliminate the possible ducting nightmare of the intake air or merely to make said ducting as short as physically possible. I think it is telling that a number of cars which featured air-to-water intercoolers from the factory - such as the GMC Syclone and Typhoon - are almost always converted to air-to-air units when upping performance is the goal. Check out an issue of Turbo magazine; you'll see these cars with huge air-to-air units mounted below the front bumber (or else behind the grill and in front of the radiator). There's a message here somewhere...

Air-to-water. If we use water as the cooling medium instead of outside air, we can see a big improvement for several reasons: Water can absorb more energy with a lower temperature rise. This improves our DTlm, makes it bigger, which makes Q go up and outlet temps go down. A well designed water cooled exchanger also has a much bigger U, which also helps Q go up. And since both DTlm and U went up, you can make the area A smaller which makes it easier to fit the intercooler in the engine compartment. Of course, there are some practical drawbacks. The need for a water circulation system is one. A big one is cooling the water down after it is heated (which means another radiator). This leads to another problem: You heat the water, and cool it down with outside air like the Syclone/Typhoon. You can't get it as cool as the outside air, but maybe you can get it within 20 degrees of it. Now you are cooling the turbo air with water that is 20 hotter than the outside air, and you can only get within 15 degrees of that temperature so coming out of the intercooler you have turbo air that is 35 degrees hotter than outside! (turbo air is 15 deg over water temp which is 20 deg over outside temp). You could have easily done that with an air to air intercooler! But... if you put ice water in your holding tank and circulate that... Then maybe the air temp coming out of the intercooler is 15 deg above that or 45 to 50 deg. Hang on! But after the water warms up, you're back to the hot air again. So, great for racing, not as good for the street.