Background:
Mabotech offers a “true” 3.5-inch downpipe for the Mk7. The emphasis on “true” distinguishes this downpipe design from some products that taper before reaching the connecting point to the midpipe.
The Mabotech 3.5″ downpipe joins to a 3.5″ midpipe, eliminating a point of restriction.
Tests with various intake setups have highlighted the significance of the outlet from the intake components, the turbo elbow (TIP) in the case of the intake, to the overall airflow.
I was curious to learn how a 3.5″ downpipe would perform compared to other tested downpipe designs.
Test Process:
The Mabotech downpipe is being tested in the same manner as other downpipes, except for the flow bench adapter, which, by necessity, has a larger diameter to fit the 3.5″ outlet of the Mabotech.
The flow bench is first checked with a calibration plate, then the Mabotech downpipe is placed over it so that air is drawn through the part in the direction that exhaust air flows on the vehicle.
The downpipe is connected to the flowbench adapter using a 3.5″ silicone coupler, and a bellmouth is placed at the inlet end of the downpipe to smooth airflow into the downpipe.
The test is performed at a depression of 10″ of H2O.
Test Results:
Note: As mentioned in the Test Process section, this test was conducted at 10″ of H2O. Testing with other downpipes has been performed at 16″ of H2O. The reason for the lower depression is that the flow bench maximum flow rate is 600 CFM, and the Mabotech downpipe flow rate exceeds this. The lower depression supports an accurate measurement of the flow rate, which is extrapolated using Bernoulli’s Equation, to 16″ of H2O for inclusion on the chart.
The Mabotech 3.5″ downpipe flows 584 CFM @ 10″ of H2O.
Extrapolating from 10″ of H2O to 16″ of H2O, the estimated flow rate is 724 CFM. This is shown on the chart below along with other downpipes that have been flow tested.
Conclusions:
The Mabotech 3.5″ downpipe was flow tested to measure flow rate and compare it with other downpipe options for the Mk7 GTI.
The Mabotech downpipe flows 584 CFM @ 10″ of H2O, approximately equivalent to 724 CFM @ 16″ of H2O.
This is the highest flow rate of all the downpipes measured as of this date. The Mabotech flows ~26% more than the next closest Trackslag catless downpipe, and provides a ~328% increase in airflow compared to the stock GTI catted downpipe.