SRM S4 Intake Manifold

Test Item: Silly Rabbit Motorsport Modified B5 S4 Stock Intake Manifold

This is a stock B5 S4 intake manifold that was sent to Silly Rabbit Motorsport to have the plenum enlarged and porting done to the runner inlets.  The inlet size is unchanged.  Thank you to Silly Rabbit Motorsport for offering to modify this item for testing.

srm_im1 srm_im2 srm_im3 srm_im4srm_im6srm_im5The Results

Flow testing was performed on a PTS orifice style flow bench at test depressions of 28″ H2O for all inlet runners open and 10″ H2O when each individual runner was tested.

All runners open
All runners open
Individual Runner Tests
Individual Runner Tests


In comparing the SRM modified IM with the extrude hone stock manifold it appears that enlarging the plenum does not aid improving airflow during this type of test.  ** It is important to remember that there are significant differences between an airflow test on a flow bench and operating on the vehicle – the enlarged plenum may very well change the performance achieved on the vehicle. **

Attributing the flow increases to the porting that was done, the results show that the SRM port work achieved results on par with an extrude hone.

Here is how the various options stack up in comparison to the unmodified B5 S4 intake manifold.

srm_overallAfter finding the median of the per runner flow increase, the results are:


RS4 Throttle Body Adapter

The SRM modified intake manifold went back to have an adapter attached that would allow it to work with an RS4 throttle body.  With this change made I was interested to see if the flow results changed.


srm_rs4tba_2Back on the flow bench the results were:

srm_rs4tba_all srm_rs4tba_runners

No different than before.

My assessment for why the same results were obtained is that the adapter does not change the size of the inlet to the intake manifold.

Audi B5 S4 Information and Testing