Modified RS4 Intake Manifold Test

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.

Modified RS4 intake manifold on flowbench
Exit velocity (FPS) measured at 3″ of H2O

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.

Modified RS4 intake manifold side shot

Modified RS4 intake manifold adapter
Modified RS4 Intake Manifold – Entry Diameter: 77mm


The Results

Intake manifold runner flow comparison

Intake manifold total airflow comparison
Intake manifold total airflow comparison – All runners open

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

Stock RS4 intake manifold
Stock RS4 intake manifold – Entry Diameter: 76mm

RS4 intake manifold comparison one

RS4 intake manifold comparison 2

RS4 intake manifold comparison 3

RS4 intake manifold comparison 4

RS4 intake manifold comparison 5