I put together another adapter today so that I could test out a highly modified RS4 intake manifold.  There’s some comparison pictures below showing this modified RS4 intake manifold alongside a stock RS4 intake manifold.

The most apparent differences between this modified RS4 IM and the stock RS4 IM are that the inlet where the throttle body mounts is larger, the adapter having holes positioned further out than the stock RS4 IM.  Interestingly the diameter of the entry area is nearly the same between the modified and stock RS4 IM’s, with only a 1mm difference, perhaps due to the porting that was done around the entry area.  It is evident that the surface of the entry area is much smoother on the modified IM than on the stock RS4 IM.  The plenum has been significantly expanded, and there has been some porting done to the trumpets inside the plenum as well as the inlet area.  The modified IM does not have the vacuum port near the left side of the entrance.

The results are interesting and pretty clearcut, though I don’t really know what they mean in terms of how these parts will compare once installed on a vehicle.

The comparison data is also shown between the S4 intake manifold that I use, which is the later design type, RS4, and modified RS4 intake manifolds.

At this point I’m unsure of what to make of the air velocity numbers.  The modified IM has outlet velocities higher than the stock RS4 IM, perhaps due to the slightly larger opening allowing more air in at the same test depression, but with the same size runners it becomes necessary for the air to exit faster.

The Results

Some pictures comparing the modified RS4 intake manifold to a stock RS4 intake manifold.

Completed flow testing on an unmodified RS4 intake manifold.

One observation while testing the RS4 intake manifold was how much further up inside the runner the fuel injector sits.  Comparing the placement to that of the S4 intake manifold the RS4 fuel injector sits approximately 40mm from the exit where on the S4 intake manifold the fuel injector is approximately 22mm from the runner exit.

Not too surprisingly the RS4 intake manifold flowed on average 27% more than the S4 intake manifold based on measurements taken at 10″ of H2O.

One interesting result from the topmost picture is the airflow velocity out of the lowermost runners of the RS4 intake manifold.  With the larger runner, as compared to the S4 intake manifold, the air velocity is even lower for a given depression.  The lower right runner had airflow velocity (feet per second) in the single digit range.

When it rains…

I went from zero intake manifolds to test out to having two RS4 intake manifolds waiting to go on the bench, each needing a different adapter from the one I’d made up for the stock intake manifold, so back to work making adapters.

More pictures from different angles to come as I get closer to testing the different intake manifolds out on the flow bench.

Starting to build an adapter for the OEM RS4 intake manifold.