Prior to installing a turbocharger on my S4 I make an effort to flow test the turbine side to see how it compares with the other turbochargers that I have tested.
For this test I run a 100 CFM calibration plate since it is the closest to where these turbo products fall out, generally around 45-55 CFM at 28″ of H2O.
Turbo Concepts Stage 1 Turbocharger on Flowbench
After performing the bench calibration I place the turbocharger onto an adapter for transitioning to the flowbench. The compressor wheel is fixed in place, I hold it still with a finger, and then I slowly run the flow bench up to 28″ recording several data points along the way.
The chart above is a consolidation of the various turbochargers that I have tested thus far. Of note, the BorgWarner RS4 K04 has been the highest flowing turbocharger that I have tested.
The Turbo Concepts Stage 1 performed similar to the FrankenTurbo and Turbo Engineers products, as well as BorgWarner K03’s, still below where the K04’s placed.
While this is a test that I don’t put a lot of stock in to give insight into how the product will perform on the car, it is notable that the exhaust backpressure measured on the vehicle has been lowest with the BW K04’s, supporting the flow bench measurement.
This time when I put the BMW MAF on the flow bench I tested the part in several configurations.
MAF with both grills in place
MAF with large space grill removed
MAF with small space grill removed
MAF with both grills removed
MAF with both grills removed and K&N filter attached
BMW MAF HousingBMW MAF Housing
The results are shown below:
BMW MAF and K&N Air Filter
For the most part the results were as expected. As the grills were removed from the MAF housing the airflow increased. The removal of the small grill led to a greater increase in airflow than the removal of the large space grill.
What was a surprise was the increase in airflow that occurred when the grill-less MAF housing had the K&N cone air filter attached. This is most likely attributable to the filter neck smoothing the airflow as it enters the MAF housing. I’m impressed by the fact that adding the air filter increased airflow, that was not the case with the stock airbox when I tested it using the EPL MAF housing.
The Nogaro project car came equipped with an unusual intake setup, a BMW Bosch MAF housing with the Hitachi Sensor epoxied into place, and a big honkin’ K&N cone filter feeding the MAF.
BMW MAF with K&N Cone Filter
This Bosch MAF has grills on both ends, which seems to me to be a bit unnecessary.
BMW MAF HousingBMW MAF Housing
It is a relatively large housing at 81.5mm in diameter on the inlet side and 83mm on the outlet side. These readings may be slightly off due to being taken with the grills in place.
I was curious how this combination would flow in comparison to a typical S4 Stage 3 setup that I would use, so I pulled the EPL MAF off the shelf along with a stock airbox. The EPL MAF has a 78.5mm inlet and 85.3mm outlet.
I first did a calibration run with a 400 CFM calibration plate on the flowbench.
400 CFM Calibration Plate
Since I was interested in seeing how the MAF and also the K&N filter performed, I first tested just the BMW MAF housing.
BMW MAF Housing
Then I added the K&N filter to the MAF and tested it again.
BMW MAF with K&N Air Filter
Next I swapped over to the EPL MAF housing. The EPL unit is sized to fit into the stock airbox and RS4 accordion.
EPL MAF and Stock Airbox
Since this airbox does not have the benefit of being modified with the “Darintake” mod I chose to leave the intake snorkel off. If it were included I would expect airflow to drop slightly from what was recorded.
Since the Darintake mod greatly helps with airflow through the airbox I did another run with only the air filter in place, simulating the effect of having the bottom of the airbox opened up.
Results:
Collecting the flow results and charting them produced the following:
EPL MAF vs BMW MAF
A few observations about this data.
The addition of the K&N filter to the BMW MAF housing did not alter the airflow reading in any appreciable way. This was a bit of a surprise, indicating that the K&N filter is less of a restriction to airflow than the BMW MAF housing.
The EPL MAF housing outflowed the BMW unit by a large amount, despite having a slightly smaller inlet. I attribute this significant difference to the grills on the BMW MAF.
The unmodified stock airbox dropped airflow through the EPL MAF housing by a great deal. This reinforces the utility of performing the Darintake mod. When this mod was simulated through use of the air filter alone the airflow jumped up becoming much closer to the EPL MAF housing alone, though not equaling that airflow.
Upon inspecting the BMW MAF housing closer it appears that the grills can easily be removed. This leads to the opportunity to test the MAF housing with different grill combinations to determine the affect of the different grills on airflow. It will also enable me to determine if the K&N cone filter becomes a restriction, relative to the MAF housing, at higher airflow rates.
