Silly Rabbit Motorsport SMIC

Today I got around to installing the Silly Rabbit Motorsport B5 S4 SMIC’s.  These have the RS4 sized inlet and outlet piping along with water/methanol bungs for use with the Aquamist injection nozzles.

SRM IC with RS4 piping & water/methanol bung
SRM IC with RS4 piping & water/methanol bung

The mounting tab on the top end tank is a nice feature for holding the intercooler steady.


For now I’ll be using them without the shrouds.  I have them but decided to hold off installing them until later.

Boost Manager Profile Analysis

With the Boost Manager operating and Aquamist’s Flow Sensor recording I logged my S4 to see how the pump duty cycle map that I had created worked out.

Boost Manager Water Methanol Injection System Profile Analysis

I’m attributing the jumpiness in the water/methanol flow to sensor noise which I hope to minimize in the future.

The water/methanol pump duty cycle map is based upon engine speed and manifold pressure (MAP).  As is shown by the left line with arrows, activation of the pump takes place around 2000 rpm once MAP reaches about 6 psi of boost pressure.

At 10% duty cycle the pump is essentially still off with respect to the flow volume, this was first shown when I conducted a calibration session with the water/methanol injection system.  I have the pump at such low duty cycle to get things moving in anticipation of the system injecting a measurable quantity of fluid shortly thereafter.

When engine rpm reaches 2500 and MAP passes 11 psi the pump duty cycle increases and the flow rate increases quickly.  The flow rate tracks with the increasing rpm, though I have some refinement to do in order to match engine speed better.

A couple of other parameters that would be useful to look into are airflow, via the MAF reading, Fuel Injector Duty Cycle, and intake air temperature.

At the right side of the chart the flow rate drops, despite engine speed increasing, because the MAP is dropping and then lowers the pump duty cycle.  This is another area of the chart that will get some attention to refine the pump duty cycle and better manage the fluid flow rate.



Exhaust Manifold Velocity

What was done:

As a follow-on to the exhaust manifold pressure drop testing that was performed I decided to use a velocity probe to assess the airflow velocity out of the exhaust manifold at a fixed airflow rate.


I still had available the AWE Tuning, Silly Rabbit Motorsport, and Audi S4 stock exhaust manifolds.

awe-tuning, srm, Audi B5 S4 exhaust manifolds
(L-R) AWE-Tuning, Silly Rabbit Motorsport, Audi exhaust manifolds

Test Procedure:

The velocity probe was placed perpendicular to the plane of the exhaust manifold outlet approximately intersecting the plane across the outlet opening.

exhaust manifold velocity probe test
Velocity probe at outlet to exhaust manifold

Due to the interaction of the airflow with the probe the readings varied slightly.  To try and minimize the affect of this variation 10 samples were taken for the AWE and SRM manifolds and averaged.  The higher velocity from the stock exhaust manifold caused greater variation and therefore 20 samples were averaged.

Only the middle primary was tested.

Here is each product on the bench as the tests were being conducted.

audi b5 s4 exhaust manifold velocity probe test
Stock Audi B5 S4 exhaust manifold
awe tuning exhaust manifold velocity probe test
AWE-Tuning exhaust manifold
srm exhaust manifold velocity probe test
Silly Rabbit Motorsport exhaust manifold

The Results

exhaust manifold velocity probe test results
Airflow velocity test results

Based on the respective diameters of the primary runners and the outlet diameter of the manifolds the results are not surprising.

Audi B5 S4