PTS Flowbench

PTS Flow Bench

Background:

The subject of flow test results and the flow bench that I use come up occasionally so this post will give some history of my use with the flow bench along with the bench capabilities.

PTS Orifice Style Flow Bench
PTS Orifice Style Flow Bench

After spending several years researching modifications to my B5 S4 by taking measurements on the car I began to wish for an easier and more accurate option for measuring airflow, use of a flow bench was the answer.

Research:

SuperFlow is a manufacturer of commercial flow benches which I looked into, but with prices ranging from $15,000 to $30,000, I decided to look for less-costly options.

On the other end of the spectrum were DIY benches that used a Shop-Vac as the vacuum source. The low cost was appealing, but so was the capability of the benches.

Another DIY option is the PTS Flowbench. The design was a result of collaboration between members of a flow bench forum. The use of the bench design by a number of performance shops that participated in the forum was reassuring that the design was sound and capable of meeting the requirements of people whose business is modifying car parts.

PTS Design:

Some examples of other people’s/shop’s PTS flow benches are shown throughout the remainder of this post. All of the examples are based on the same design, with some having customizations.

PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench

With the goal of flow testing various automotive parts that would carry a high airflow, I elected to install the maximum number of motors the bench will fit, eight (8).

This number of motors enables the flow bench to operate at 28″ of water depression while flowing just over 600 cubic feet per minute of air.

Note: While the depression the bench is operated at is described using inches of water, no water is used in the flow bench.

For under three thousand dollars, and leveraging some knowledgeable help with the construction, I was able to build a bench that performs equivalent to the SuperFlow SF-750 flow bench.

PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench

Support Equipment:

The PTS Design bench uses an internal orifice plate, and I have additional orifice plates for checking the calibration of the bench.

Blaze Adapter Test - Bench Calibration Check
Orifice Plate

A Digital Manometer is used to measure air pressure at three locations within the bench to determine the pressure drop across the part being tested.

PTS Digital Manometer
PTS Digital Manometer

The Digital Manometer has a range of up to 36″ of H2O, but a common standard depression is 28″ of H2O and this is what I mainly use for testing.

There is also a sensor port for measuring airflow velocity with a pitot probe.

Pitot Probe

Making an adapter to join parts to the flow bench was a challenge for the first few years that I was testing parts. Plexiglass and wood were the materials I had to work with and making adapters was laborious and imprecise.

The availability of lower-cost 3D printing tools transformed what was possible. I now use a Prusa i3 Mk3S printer to print adapters as well as prototype parts.

Prusa i3 Mk3S 3D Printer
Prusa i3 Mk3S 3D Printer

Freely available software applications such as Tinkercad and OnShape have made designing complex parts for printing simpler.

Powering the flow bench is not as simple as plugging it into a household outlet. At each home where I’ve used the flow bench I’ve needed to have an electrician install an additional outlet and modify the house circuit breaker panel to support a 240-volt 40 amp outlet.

Flowbench Power
Flowbench Power

Results:

The flow bench has proven to be a great time saver as well as being much more reliable at measuring airflow through components. The signal-to-noise ratio, or the “difference to detect” and “system noise”, is much more favorable using the bench compared with recording indirect measurements on the GTI.

A strong correlation between the flow bench measurements and those using the vehicle has been demonstrated in comparing intercooler pressure drop and intake pressure drop with measures recorded using the GTI:

Bench vs Street Pressure Drop Correlation
Flow Bench Airflow vs Vehicle Operating Pressure Drop Correlation
APR vs Modified Stock Intake
Acceleration Rate vs Intake CFM Flow Rate

Note: Similar to a dynamometer, the best use of the flow bench is for detecting changes. This aids in ranking relative performance. The magnitude of a measurement is not particularly useful unless it is compared with another measurement.

PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench
PTS Design Flowbench

The PTS flow bench has been very useful for comparing airflow-carrying parts under well-controlled conditions with the ability to detect small changes in performance.

References:

For questions about the PTS Design flow bench, I recommend checking out the:

PTS Flowbench forum

Some books I’ve found helpful on the subject of using flow benches for modifying automotive parts:

Airflow reference books
Airflow reference books