Audi B5 S4 2.7t – Effect of Intake Air Temperature (IAT) on Engine Performance

Over the course of tuning a K04/RS6 equipped Audi B5 S4 2.7T I have acquired hundreds of logs in a variety of different ambient air temperatures. Organizing the data demonstrates the effect of intake air temperature (IAT) on engine performance.

Within the B5 S4 community, a “FATS” time is a arbitrary measure of performance that consists of a third gear pull from 4,200- 6,500RPM (~60-95mph). A lower FATS means the engine produced more power.

This demonstrates a clear increase in power as IAT was reduced. These particular logs were taken with the same boost curve and 91 octane fuel across the temperature range. Most of performance increases can be attributed to denser air and increased ignition timing as the IAT temperature decreases.

An estimation of power and torque based on vehicle acceleration suggests a difference of 100ft/lb at the wheels between IAT’s of 40 degrees fahrenheit and 120 degrees fahrenheit.

IAT 40 degrees fahrenheit
IAT 120 degrees fahrenheit

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