Previously a CTS Turbo 3.5″ cat-less downpipe was flow tested and I am interested to learn how the 3″ ARM cat-less downpipe compares.
First, the flow bench is checked for accuracy using a calibration plate.
Next, the downpipe is attached to the flow bench using a silicone coupler that is the same 3″ diameter as the piping at the outlet end of the downpipe.
A bell-mouth is attached at the inlet to smooth airflow into the downpipe.
The flow bench is operated at a depression of 16″ of H2O and the airflow measured at that depression is recorded.
The ARM Motorsport cat-less downpipe flows 520 CFM at 16″ of H2O.
This result is compared with the stock GTI downpipe, which has two catalytic converters, and the CTS 3.5″ cat-less downpipe, below:
The airflow measurements from a few other downpipes that were tested in this manner are shown below:
The ARM cat-less downpipe flows 520 CFM @ 16″ of H2O.
This is roughly a 200% increase over the stock GTI downpipe. Compared to the ARM Motorsport catted downpipe the cat-less model increases airflow by approximately 35%.
Comparing the 3″ ARM downpipe to the CTS cat-less downpipe that has a 3.5″ inlet there is no significant difference in airflow at the test depression.