All of the turbochargers I have had my hands on lately have been put on the flowbench to have the airflow through the turbine housing recorded.
The most recent B5 S4 suitable turbocharger to show up is a pair of the Audi RS6 K04 turbo’s. Because in OEM form these will not fit on the 2.7T engine this pair has been modified to work with B5 S4 components.
Unlike with the TTE turbo’s that also showed up with turbo to downpipe studs firmly stuck in the turbine housing, I chose not to pay a shop to remove the studs out of the RS6 turbo’s turbine housing. Instead I’ve modified the adapter used to attach the turbocharger to the flowbench to accommodate the studs.
Following alteration of the adapter I went through the normal process of testing an article on the flowbench, beginning with a calibration test. Results of the flow test are shown below:
It is clear that the airflow through the RS6 turbine housing is substantially greater than of that through the RS4 K04 and FrankenTurbo F21 turbochargers. (The F21, TTE550, and TC Stg1 flowed approximately the same so I have omitted the TTE550 and TC Stg1 data from the chart to make following the lines easier.)
I have found the results on the flow bench to correlate with the exhaust back-pressure readings that I have made on my S4. That the RS6 K04 turbocharger is able to flow higher than RS4 K04’s comes as no surprise, the magnitude of the increase is the most noteworthy finding from this test.