Baun Performance DP Flow Test


Baun Performance sells a 400 CPI GESI catted downpipe and an accompanying 3.5″ resonated midpipe for the Mk7 GTI.

I had concerns that future tunes using the Cobb Accessport may cause the CEL to illuminate if I continued to use a Trackslag catted downpipe, so I switched over to the Baun Performance setup.

Baun Performance and Trackslag Downpipes
Baun Performance and Trackslag Downpipes

The upper section of the Baun Performance downpipe is 4″, similar to the Trackslag, but the catalyst is 400 CPI in a 4.5″ diameter housing versus the Trackslag at 200 CPI and 5.25″ diameter housing.

Baun Performance 4" GESI Downpipe & 3.5" Resonated Midpipe
Baun Performance 4″ GESI Downpipe & 3.5″ Resonated Midpipe

Since I was making the swap between downpipes I conducted a flow test of the Baun Performance setup before installing it on my GTI.

During the process of configuring the part to test, I noted that the inside diameter of the inlet of the Baun downpipe is a little smaller than the Trackslag.

Baun Performance Downpipe Inlet Diameter
Baun Performance Downpipe Inlet Diameter

This became evident when I attached the bellmouth that I use for smoothing airflow entry at the downpipe opening. The bellmouth was slightly larger than the Baun DP.

Downpipe Test Bellmouth
Downpipe Test Bellmouth

Attaching the bellmouth to the turbine outlet of the turbocharger showed that the bellmouth is also larger than the turbo outlet.

Bellmouth compared with turbine housing outlet
Bellmouth compared with turbine housing outlet

What I learned from this is that the Baun downpipe has an opening that is the same size as the outlet from the turbine housing, and the Trackslag is slightly larger than the turbine outlet. The bellmouth has been made slightly larger than the outlet of the turbo since I based the design on the Trackslag downpipe inlet.

In a standalone test like this, where the downpipe is being tested with a bellmouth adapter that is slightly larger than the turbocharger outlet, it’s likely that this will be beneficial for the Trackslag downpipe and not as much for the Baun Performance downpipe.

A better configuration would be with the bellmouth sized similar to the turbocharger outlet and not the Trackslag downpipe inlet. At the time that I got around to testing the Baun downpipe, the Trackslag was gone and it could not be retested.

Other product design advantages related to pressure drop that the Trackslag has are the 5.25″ diameter catalyst versus the 4.5″ GESI cat, and half as many cells per inch, 200, compared with the Baun GESI cat at 400 CPI.

Test Procedure:

After checking the flow bench with a calibration plate the Baun Performance downpipe is assembled and attached to the flow bench and the bellmouth is placed at the inlet.

Baun Performance GESI 4" Downpipe Flow Test
Baun Performance GESI 4″ Downpipe Flow Test

The bench depression is increased to 16″ of H2O and the airflow rate at this depression is recorded.

Next, the mid-pipe is attached to the downpipe and the assembly is joined with the flow bench.

Baun Performance Downpipe and Midpipe Flow Test
Baun Performance Downpipe and Midpipe Flow Test

Note: This mid-pipe is 3.5″ until after the bend where it joins with a catback exhaust. At the bend it transitions to 3″ to work with an AWE catback, which I use, or a Baun exhaust. Baun also offers a mid-pipe that is 3″ throughout.

These parts are tested at 16″ of H2O.

Test Results:

The Baun Performance downpipe with GESI cat flows 396 CFM @ 16″ of H2O.

This measure is shown with other catted downpipes that have been flow tested in the manner described above.

Adding the resonated mid-pipe, which includes a reducer down to 3″, results in an airflow rate of 338 CFM @ 16″ of H2O.


The Baun Performance 4″ GESI cat downpipe was the subject of a flow test. At a test depression of 16″ of H2O the Baun downpipe flows 396 CFM when configured as described above.

This flow rate is approximately 143% greater than the stock GTI downpipe.

Out of four aftermarket catted downpipes that have been tested, this is the second-highest airflow rate that has been measured. Notable about this ranking is that all of the other catted downpipes were 200 cells per inch and the GESI catalyst is 400 cells per inch.

It’s likely that the difference between the Baun DP and slightly higher flowing Trackslag downpipe would be decreased if a bellmouth adapter were made using a diameter equal to the turbocharger turbine housing outlet and the products retested.


2 thoughts on “Baun Performance DP Flow Test”

  1. Just a quick “thank you” for conducting this testing and making it available. You have solidified my decision to purchase the Baun DP + exhaust.

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