Background:
The ARM 4.5 inch DP for the Mk7 was recently released, and ARM Motorsports contacted me to ask if I would conduct a flow test with the new downpipe.
This downpipe is unique in terms of size, which piqued my interest in testing it to see how it compares with some of the other downpipes that I have flow tested.
One of the other downpipes I have tested and used regularly is the Baun Performance 4″ GESi Catted downpipe. It is shown in the picture below, along with the ARM DP for size comparison.
Test Process:
The ARM downpipe would be flow-tested with a PTS flow bench using a stock exhaust adapter and a 3″ exhaust adapter.
Spoiler alert: The stock adapter test is not shown on the chart below because it does not flow as well as the 3″ exhaust adapter.
The downpipe is placed above the flow bench so that the outlet of the pipe flows directly into the bench through a silicone coupler and an adapter.
At the entry of the downpipe, a bellmouth is placed to smooth the path of air being drawn through the downpipe.
The downpipe is tested at a depression of 16″ of H2O.
Test Results:
The ARM 4.5″ DP with the stock exhaust adapter flows 450 CFM @ 16″ of H2O.
With the 3″ exhaust adapter attached, the ARM downpipe flows 568 CFM @ 16″ of H2O. This is a very small difference from the Trackslag catless, which has the highest airflow reading of the tested products.
Operational impact:
The following chart shows one example of the scale of change the improved exhaust airflow can produce. It compares my Mk7 GTI with a Mabotech M520h hybrid turbo operating around 30-31 psi when the downpipe changes from the catted Baun Performance to the catless Trackslag.
The turbocharger wastegate duty cycle decreases by approximately 5-10%.
This scale of change, or greater, to the turbocharger WGDC should be expected from the ARM 4.5″ DP when switching from a high-flow catted downpipe on a turbocharger of this size.
Conclusions:
The ARM Motorsport 4.5″ catless downpipe was the subject of a flow test.
When fitted with a 3″ exhaust adapter, the ARM downpipe flows 568 CFM @ 16″ of H2O. A stock exhaust transition reduces the airflow rate to 450 CFM @ 16″ of H2O.
The ARM 4.5″ downpipe flows approximately the same as the highest-flowing downpipe tested. Compared to a high-performance catted downpipe, the ARM catless downpipe should produce more efficient turbocharger turbine operation.