IC Temperature Efficiency

As a follow up to the discussion about the Audi B5 S4 Stock Intercoolers here is a chart that illustrates just how effective all of the available intercoolers are at dropping the charge temperature.

Temperature Drop of Intercoolers
Example of Temperature Drop achieved by Intercoolers

The chart above is a composite of several pieces of data to be illustrative of how effective the intercoolers are at achieving temperature drop in the charge air.

The measured compressor outlet temperature rise and IAT curve showing a 12 degF rise were recorded together on a stock boost (8 psi) pull.  The curve showing a 28 degF IAT rise is from an S4 operating at 21 psi of boost pressure with stock IC’s.

On a typical stage 3 S4 operating with K04 size turbo’s it would not be unusual to see the intake air temperature increase by 28 degF by the end of a FATS pull.  This is the 28 degF curve shown above.

Under similar conditions an ER intercooler would be expected to show a temperature rise in the neighborhood of 12 degF, shown by the second IAT curve above.

Typically an Intake Air Temperature comparison would show these two curves with an appropriate scaling that highlights how the Stock intercoolers allow IAT to rise more the twice what ER’s do – the impression that the divergent curves give is that there is a substantial performance difference between the two intercoolers.

When the turbo compressor outlet temperature is included, as above, some additional perspective is available.  It becomes evident that both the Stock and ER intercoolers are dropping the charge temperature a significant amount – with a stock boost level the IC’s lower the charge temperature by roughly 100 degF.

But as I pointed out, the 28 degF IAT curve was obtained with Stock intercoolers at 21 psi of boost – a case that I have not yet measured the compressor outlet temperature for.  Based on predicted outlet temperature the blue dotted line shows what the compressor outlet temperature might look like at 21 psi of boost.

Knowing that stock IC’s show a 28 degF delta and ER’s a 12 degF delta when recorded on a FATS pull at 21 psi of boost, the amount of temperature drop from the compressor outlet is around 170 degF for stock IC’s and 186 degF for ER’s.  As the far right markings on the chart show, there is a big drop in temperature whether by the stock IC or the ER, and the difference in performance of the Stock IC and ER IC is relatively small in comparison to the amount of total temperature drop being achieved.

Bottom Line:

Both of these intercoolers are doing a good job at temperature drop.  The aftermarket intercooler is able to achieve greater temperature drop than the stock IC, but in the context of the overall temperature drop of the charge air the differences between the two products is not that great.