Looking at different aspects of intercooler performance led to making a chart showing the temperature exiting the intercooler and the intake air temperature. The intent was to determine if how quickly IAT dropped would be a useful measure of intercooler performance.
The intercooler outlet temperature (IC_Out) is being measured with a temperature probe located in the cold side charge pipe. The intake air temperature (IAT) is recorded by the vehicle intake air temperature sensor located in the intake manifold.
At the start of this test the IAT is reported as 97F and the IC_Out is 85F. Outside air temperature (OAT) reported by the vehicle sensor is 79F.
After boost builds the temperature out of the intercooler increases slightly for approximately 1 second while the IAT steadily decreases.
At halfway through the pull the IAT approaches the IC_Out and thereafter both readings decrease together and hold steady.
Overall the IC_Out temperature drops approximately 4 degF and the IAT drops 13 degF.
Conclusion:
Rate of IAT drop is not a good measure of intercooler performance due to the inaccuracy of the IAT sensor measurement.