Objective:

Determine if porting and polishing the stock exhaust manifolds results in a change in the airflow through the individual manifold runners in comparison to an unmodified stock Audi B5 S4 exhaust manifold.

Articles:

Up for testing is a stock OEM Audi B5 S4 exhaust manifold and a similar product that had porting and polishing work performed on it.  The ported and polished exhaust manifold also had a ceramic coating applied giving it a black color.

The key differences between the manifolds is at the entry to the runner.  The difference in the inlet is subtle, but can be felt, with the ported inlet having less of a lip at the inlet.

Testing:

Both exhaust manifolds were tested on the PTS Flowbench at 28″ of H2O.  Individual runners were tested with non-tested runners blocked off.

Results:

The results of the stock versus ported exhaust manifold flow test are shown below.

There is essentially no difference in performance between the stock exhaust manifold and the manifold with porting and polishing work.

Conclusion:

It does not look like porting and polishing of the stock exhaust manifolds is a worthwhile modification absent any other changes.

Perhaps if the cylinder head exhaust ports were enlarged and port matching was then performed on the exhaust manifolds that some difference might be recordable.