RS4 IC Flow Test

I received a set of Audi RS4 intercoolers courtesy of Matt Danger on the Quattroworld forum.  Matt deserves a big thanks for supplying the intercoolers as well as paying for all of the shipping, to me and back to him, which goes a long ways toward enabling me to put the donations I’ve received toward additional testing opportunity’s.  Thanks Matt!

By now what I am doing should be understood so I’ll skip rehashing my goal.  If you haven’t been following along I recommend reading over the Stock, ER, and AMD flow test pages which were tests conducted prior to this test.

A couple of points to emphasize about this testing.

Flowbench is like a dyno

First, similar to a dyno test, the real value lies in conducting repeat tests with the same test equipment on different test articles.  Trying to compare results from my flowbench to another, such as a SuperFlow 600, may or may not produce like results.  The absolute numbers are not as important, nor as reliable, as the relative performance results of the intercoolers being tested.

Estimating values

Another point concerning the results is that the pressure loss curves show measured and calculated values.  This is because after a specific level of pressure differential is reached inside the flowbench the digital manometer’s sensor maxes out.  The manometer design is aimed at measuring flow rates at 28″ of water which is a very common test point.  What I am doing is slightly out of the norm for a flowbench in that I am trying to flow as much CFM as possible and record the pressure losses across a test article (intercoooler).  Because the intercooler presents a good amount of back pressure the sensor is maxed at airlfow values well below what would be seen on the car.  To attempt to provide some idea of how much pressure loss might be encountered when equipped on an S4 I have used a least squares fit to predict where the pressure loss curve would be at higher airflow rates.  Predicting beyond the measured data is an imprecise estimate, but by using the same method for each test case the relative values will remain accurate, the absolute pressure loss readings may not be exact.

Pressure loss only

Finally, pressure drop performance and temperature drop performance are inextricably linked.  As you look at the pressure loss results keep in mind that the real power of these airflow tests is using them in conjunction with temperature data.  With those two performance aspects understood it is possible to make a much better informed decision about what intercooler is best suited (performance wise) to your own application.


The keen eyed reader will see that I’ve switched the stock passenger and driver data labels.  I had shown them reversed previously.

I’ve broken out passenger and drivers side onto separate charts to try and reduce some of the clutter.  Also, as I continue to add more data to the charts the color scheme and order of presentation keep changing, I’ll try to not do that in the future if I can help it.

And the latest results…

Summary of flow results to date

Driver's side pressure loss
Driver’s Side


Passenger's side results
Passenger’s Side


The disparity in flow rates between the passenger and driver side of the RS4 intercoolers did not go unnoticed while I was testing.  It seemed odd since the two cores were very similar with equally similar end tanks.  The difference in flow rates produced by the stock intercoolers seem to be from the end tank design, but the RS4 intercooler’s end tanks are very similar.

Inspecting the RS4 intercooler driver’s side part showed that it had some damage which could have caused some restriction to one of the airways.  My conclusion is that the damage to the driver’s side core is causing it to flow less than the undamaged passenger’s side core and if the damage were not present the driver’s side would flow more, likely equaling the flow rate of the passenger side intercooler.

Checking with Matt he confirmed the intercooler had been damaged at one point and repaired.

RS4 intercooler driver's side front
Driver’s Side Front View
Driver's side rear view
Driver’s Side Rear View

Audi B5 S4 Information and Testing