Three intercoolers I’ve hung onto to conduct additional evaluation with are the APR, do88, and IE v1 stock location replacements.
Each have been in the GTI for a period of time that has allowed for gathering more data.
The data I presently use for comparison is generated from a full throttle third gear pull. The intake air temperature minus the ambient air temperature at 6,000 RPM is the value used for comparing the intercoolers.
A series of pulls made at different times for each intercooler is the source data for this comparison.
The chart below shows the data for each of these intercoolers in a box plot. The number following the brand in the title is the number of data points recorded for that product.
There is a 5 degree Fahrenheit range between the average temperature deltas for all three products.