Why ER Intercoolers?

Disclaimer : The author of this page is not versed in fluid dynamics or any other scientific background applicable to these tests, and is not qualified to explain in scientific terms the causes of the results found here.  However, the author doesn't care as the he is only interested in the results themselves.  If you, the reader, have scientific theories and/or complex formulas to explain the results, please feel free to discuss these ideas on your favorite automotive and/or fluid dynamics enthusiasts internet forums.  If you find incorrect spelling or improper grammar on this page, please do not fret.  If you are still fretting, please close your browser, power down your computer, and curl up by the fireplace to peruse your favorite edition of the dictionary.

The data in the charts here were collected by ECU Explorer, an application developed and sold by APR.  This product may or may not still be for sale.  If you work for APR and would like to clear this up, please contact me.

The charts on this page come from a Microsoft Excel template created and maintained by Mark P.  Mark is kind enough to make this available free of charge.  Thank you Mark!


Car 1: 2001 Audi S4
Power Affecting Mods: Plain Jane (unmodified) K04 turbos, Piggie Pipes (downpipes with pre-cat removed), and Autospeed Performance cat back exhaust.

Red and Pink: OEM S4 Intercoolers
Blues: ER Intercoolers

Sometimes we find a trade-off with intercoolers which do a good job of keeping the Intake Air Temperature (IAT) low.  A larger capacity intercooler can cause pressure loss across the core(s) or delayed boost response.  Immediately below this text block is a boost chart comparing the two sets of intercoolers.  Please note that unfortunately during testing the exact same RPM was not able to be used as a starting point.  This is the reason for the discrepency seen below as to when the boost is ramping up.  We can see below that there was no loss in pressure. Isntead we see a slight gain in pressure and a strange boost dip that occured after 4000 RPM has gone away.  Please also refer to the N75 duty cycle chart just below this boost chart.  Note: Boost pressure is measured by the OEM MAP sensor located immediately preceding the throttle body.


You can see with the N75 chart that through the mid section there was actually slightly less N75 duty which acheived a slightly higher actual boost value.



Another possible problem with poorly designed intercoolers is they can restrict air flow.  Below is a chart of data logged from the Mass Airflow Sensor (MAF or MAS).  We can see that there was consistently more airflow across the MAF with the ER Intercoolers vs the stock units.



Now that we've made sure we don't have a pressure loss or flow restriction compared to the stock units, let's take a look at the actual IATs.  Please note that the ambient air temperatures between these comparisons were within just a few degrees.  We can see the ER units have quite an impact on the IATs.  At the request of automotive enthusiast forum members, the author of this page put together a recovery chart to show how long after a run it takes for the intake air temperatures to fall back to the temperature they were at the beginning of the run.  I had a good chuckle at myself when I plotted up a straight line.  Recovery time was pretty much non-existent, since the delta between start and end are virtually nil.



Finally, what does all this mean for actual acceleration?  The S4 community has a method of measuring acceleration of the car by measuring the amount of time required to accelerate from 4200 RPM to 6500 RPM in 3rd gear on a flat road.  This has been named FATS which is an acronym for "For the Advancement of The S4". The runs in these logs were done back and forth on the same road, both directions with each set of intercoolers.  The results were astounding to say the least.  Nothing else on the car changed between the intercooler swap, and all logs were done with the same 2 people in the car.




Let's move on to another car.

Car 2: 2001 Audi S4 Avant
Power Affecting Mods: K04/RS6 hybrid turbos with exhaust side clearanced, X1 intake, Autospeed Performance downpipes with high flow cats, AWE Twin2 cat-back exhaust

Red and Pink: OEM S4 Intercoolers
Blue: ER Intercoolers

Boost Check.  More boost gain on this car.  Interesting.  Refer to N75 Duty chart below this one


Same exact N75 duty (Hey look, the hybrids don't have to work so hard for boost)


Interestingly, we don't see the MAF increase on this car as we did on the previous.


Here again we see much improved IATs


And acceleration difference.  Not quite the gain we saw on the 1st car, but a decent gain none-the-less.  (Side note, this car has since been converted to the EPL Stage 3 fueling kit and is currently running consistent sub-3 FATS with two people in the car)



More data may be added to this page at some point in the future as more testing is done on different cars.