Exhaust Manifold Velocity

What was done:

As a follow-on to the exhaust manifold pressure drop testing that was performed I decided to use a velocity probe to assess the airflow velocity out of the exhaust manifold at a fixed airflow rate.


I still had available the AWE Tuning, Silly Rabbit Motorsport, and Audi S4 stock exhaust manifolds.

awe-tuning, srm, Audi B5 S4 exhaust manifolds
(L-R) AWE-Tuning, Silly Rabbit Motorsport, Audi exhaust manifolds

Test Procedure:

The velocity probe was placed perpendicular to the plane of the exhaust manifold outlet approximately intersecting the plane across the outlet opening.

exhaust manifold velocity probe test
Velocity probe at outlet to exhaust manifold

Due to the interaction of the airflow with the probe the readings varied slightly.  To try and minimize the affect of this variation 10 samples were taken for the AWE and SRM manifolds and averaged.  The higher velocity from the stock exhaust manifold caused greater variation and therefore 20 samples were averaged.

Only the middle primary was tested.

Here is each product on the bench as the tests were being conducted.

audi b5 s4 exhaust manifold velocity probe test
Stock Audi B5 S4 exhaust manifold
awe tuning exhaust manifold velocity probe test
AWE-Tuning exhaust manifold
srm exhaust manifold velocity probe test
Silly Rabbit Motorsport exhaust manifold

The Results

exhaust manifold velocity probe test results
Airflow velocity test results

Based on the respective diameters of the primary runners and the outlet diameter of the manifolds the results are not surprising.

Project: B5 PB550

A few more months have passed and another option has popped up, this one from Project: B5 – a turbocharger called the PB550.

Project: B5 PB550 Turbocharger
Project: B5 PB550 Turbocharger

Looking at this offering and comparing it to the Project: B5 RS6-X it is not immediately clear what distinguishes these two products.  I have tried contacting Project: B5 to find out what the differences are but have not had any reply back to my inquiries.  Looking at the two product write-ups it seems that the two differ in the following ways:

  • PB550 uses a K04 style billet compressor wheel.
  • RS6-X uses a double stack RS6 style compressor wheel.
  • The RS6-X has a clipped turbine, the PB550 does not.

At this point I have never seen any data on an RS6-X turbocharger or the PB550.  Based on the specs they are still in the region I consider a candidate system, but the lack of data and lack of communication from Project: B5 make it unlikely I would purchase one of these.

As for now the candidate list is:

  • BorgWarner K04 (great amount of data)
  • FrankenTurbo F21/MF (minimal amount of data)
  • ProjectB5 RS6-X/PB550 (no data)
  • SRM Billet K04 (no data)
  • TTE 550 (minimal data)