Effectiveness is defined as the ratio of how many degrees of temperature that were removed from the charge air by the intercooler to the original temperature that is put into the charge air by the turbo. Example: If the turbo compresses the charge air to a temperature of 140° F, but after passing through the intercooler the air is 115° cooler (resulting in a 25° F charge air temperature), the efficiency would be: Effectiveness: 115/140 = 0.82 or 82% efficiency Typically, air-to-air intercoolers for normal street applications range between 60% and 70% efficiency. Often, liquid-to-air intercoolers have effectiveness ratings from 75% to 95%. One common method of improving the cooling of the charge air dramatically in an air-to-water intercooler is the inclusion of ice as a coolant.

turbobygarrett.com