Audi B5 S4 Prototype Y-Pipe Flow Test

Flow Testing Y-Pipe Prototypes


It’s been some time since I tested any parts for the B5 S4 but when I was contacted by Torque Factory (TF) Consulting wondering if I would be willing to flow test a Y-pipe they are developing I agreed to.

Audi B5 S4 Y-Pipe Flow Testing
Y-Pipe Flow Testing

Previously I have tested the stock S4 Y-pipe as well as the B5 RS4 Y-pipe. For this test the products would consist of the Torque Factory prototype as well as The Tuner Y-pipe.

Audi B5 S4 The Tuner Y-pipe
The Tuner Y-pipe

Two MAF pipes were supplied, one 4″ and the other 4.5″ in diameter. The 4.5″ pipe contains a removable flow straightener.

Because these products are larger than the S4/RS4 parts I have previously tested I needed to make a new adapter to attach the products to the flow bench.

Flow Bench to MAF Pipe Adapter

3D printing comes in handy for creating the adapters needed to join parts with the flow bench.

Test Procedure:

Prior to measuring the airflow through the parts a calibration plate is installed on the flow bench to check for accuracy. Once that has been completed the Y-pipe is attached to the MAF pipe using a silicone coupler and the MAF pipe is attached to the flow bench using another silicone coupler that attaches to the flow bench adapter.

A MAF sensor is installed in the MAF pipe and the PCV port on the Y-pipe is blocked off.

The previous testing with the S4/RS4 Y-pipe had been performed at a depression of 10″ of H2O. I found with the larger components used during this test that the flow limit of the bench, roughly 650 cubic feet per minute (CFM), was being met before reaching 10″ of pressure drop through the test article.

Audi B5 S4 THE-Tuner Y-Pipe Flow Test
THE-Tuner Y-Pipe Flow Test

For this reason 6″ of H2O was chosen as the default test depression for taking measurements.

Several combinations of Y-pipe and MAF pipe were flow tested.

Torque Factory Consulting Y-pipe Flow Test
Torque Factory Consulting Y-pipe Flow Test

Test Results:

The table summarizes the readings for each of the combinations tested:

Test Case
MAF PipeFlow
@ 6″ of H2O

This data is presented in bar chart format along with the measurements for the S4 and RS4 Y-pipes:

Torque Factory Y-Pipe Flow Test Bar Chart
Flow Test Results Summary

A calculation can be made with the measured data to predict the airflow at a higher depression than what was tested.

Because the S4 and RS4 Y-pipes were tested at 10″ of H2O an extrapolation is made with the data for the Torque Factory and THE Tuner Y-pipes to estimate what they might flow at a depression of 10″ of H20.

The predictions are shown on the chart below, represented by the segment of the lines that are dashed.


A flow bench test was performed to measure the airflow through different combinations of Y-pipe and MAF pipes using a Torque Factory Consulting prototype Y-pipe and a production version Y-pipe manufactured by THE-Tuner.

Comparing the results of this test with previous results using the S4 and RS4 Y-pipes both the Torque Factory and THE-Tuner Y-pipes flowed significantly more air at the test depression.

Of the various combinations tested, the Torque Factory prototype using a 4.5″ MAF pipe without a flow straightener produced the highest airflow, 686 CFM @ 6″ of H20.

Audi B5 S4 Prototype Y-Pipe Flow Test
Prototype Y-Pipe Flow Test


THE-Tuner product page

Torque Factory Consulting