What was done:

To get an idea of how much heat the exhaust manifold gives off during routine driving I placed a high temperature thermocouple close to the passenger side exhaust manifold surface.

I then drove the car for approximately 30 minutes logging the final ten minutes.

Initial driving was easy to allow the engine to warm up and then I conducted a few short third gear pulls up to the 5000 rpm range to see what would happen with the near exhaust manifold temperatures under a brief heavy load.

The Results:

The chart below show the changes to the near exhaust manifold temperatures during this drive.

I was not expecting such cool temperatures near the exhaust manifold, cool being a relative term, but in comparison to what I have logged as exhaust gas temperatures (below) the temperature outside the manifold is not relatively high.

Shown below is a close up of the near surface temperature during the drive above.

I’ve made a point to call out the temperature as near surface because of the alignment of the temperature probe and the curvature of the exhaust manifold surface it was not possible to have the probe flush against the exhaust manifold exterior.  With only a small segment of the probe in contact with the exhaust manifold there was some length of the probe that had an air gap.

Observations:

It looks like the double walled OEM exhaust manifolds do a good job of keeping interior exhaust gas temperatures from reaching the engine compartment.

Temperature spikes in the exhaust gases during high load conditions do not register at all at the temperature probe.  It is possible that during these high load conditions, where the vehicle is accelerating rapidly, that there is additional airflow through the engine compartment which can carry away the additional heat.  If that were the case I would expect the exhaust manifold to remain at an elevated temperature for a short time after the high load condition, and with the vehicle decelerating the temperature at the probe to rise.  Because that does not appear to happen I believe the exhaust manifold surface temperature does not fluctuate rapidly with the interior temperatures.

After installing the EPL MAF housing, 034 Silicone MAF Hose, and RS4 Y-Pipe I took some more exhaust manifold surface temperature readings with the IR thermometer.

Results were consistent with the last time.

What’s being done:

Following up on the prior days data logging with the Darintake modified airbox I drove today with the airbox taped up.

Results:

In the morning the results were (ambient temps rising from 76 to 81F):

In the afternoon the results were (ambient temp fluctuating between 86-88F):

Comparing the results from the Darintake logging with the sealed airbox logging produced the following charts, first the morning:

Here is a comparison of the afternoon results:

Finally, I looked at periods of rapid temperature rise, associated with periods where the car was slowing or stopped, and noted the start and end times of the temperature rise along with the amount of temperature rise.  From this information I calculated the increase in degrees Fahrenheit per Second for each configuration; the Darintake airbox and the sealed airbox.

Plotting the data samples for each configuration in increasing order produced the chart below:

If the average rise rate of each configuration is calculated, the results show that the sealed airbox enables the air temperature probe in the air filter to heat up 75% slower than the rate at which the Darintake modified airbox heats up.

Conclusion:

The Darintake may be a no-brainer modification to make to the stock B5 S4 airbox if the goal is to increase airflow through the airbox.  In fact prior airflow testing of the airbox in different states of modification illustrated the benefit of the Darintake for increased airflow.  But if keeping the temperature of the intake air low is the goal, putting holes in the airbox does not help the cause.

Future Investigation:

Based upon these results I am now curious about the potential benefits of a cold air intake, and whether they would be realized.