I’ve gone and relocated the Auber Temperature probe from the exhaust manifold to inside the Airbox.  I stuck the tip of the probe between a couple of pleats of the stock air filter and then went out for a drive to see what it recorded.

At the start of the drive I was thinking that the current setup of stock airbox with Darintake mod holes cut into it was doing a fine job at allowing the air to stay close to the outside air temperature

I then stopped for a little while to see how the temperature responded.  Knowing that the exhaust manifold is right beside the airbox, how hot that gets from prior testing, and the fact that I have a bunch of holes in the bottom half of the airbox that allow hot air coming from the exhaust manifold to easily enter the airbox, I was thinking I was probably going to see the temperature in the airbox start to climb – which it did.

I was hopeful that once I started moving again and cooling air started to pass back through the engine compartment that the temperature inside the airbox would come down quickly.  It did come down relatively fast, though I was hoping for faster.  It also did not quite make it back to the starting temperature, but with a bit more driving I expect that it would have.

This experiment has prompted me to think more about the possible benefits of a Cold Air Intake (CAI) in comparison to using the stock airbox.  Alternatively I’d like to try and modify the airbox further so that the lower intake holes only open when the additional airflow is needed, similar to the valve on the bottom half of the RS4 airbox.  I’m wondering if always allowing hot air from the engine compartment into the airbox is the main driver for the temperature rises I recorded during this drive.

I conducted some additional tests documented in this post.

Today I made a couple of drives logging the temperature near the exhaust manifold, approximately 2.25″ from the exhaust manifold to the temperature sensor probe, and of the exhaust gas temperature inside the exhaust manifold.

This is a follow on to the recording I made the previous day.

The charts below were taken with ambient temperatures of 85F and 94F, top and bottom chart respectively.

The charts show the vehicle speed and temperature outside of the exhaust manifold along the left vertical axis, and the right vertical axis is the scale for the exhaust gas temperature.  The horizontal axis is time in seconds.

The exterior temperature spikes when the vehicle slows, where the quantity of cooling air would decrease.

I’ve been interested in learning if putting a thermal coating on the exhaust manifolds makes any significant difference in the temperature radiated from the exhaust manifolds.

As luck would have it I have a set of ceramic coated exhaust manifolds, but at the time that I had acquired them I was on a tight schedule replacing turbo’s on the S4 and so I had not been able to establish some good baseline data.

Additionally I’ve found that people modifying theirs cars are a very optimistic group.  If I was to use an Infrared thermometer to take external temperature readings of the exhaust manifold at various points in time, and find no difference between the thermally coated manifolds and stock uncoated manifolds, the optimists would pronounce that the surface temperature of the exhaust manifold is not important, it is what happens to the temperature of the gasses inside the exhaust manifold that matters.  If I was to measure the exhaust gas temperature of the thermally coated manifolds against the stock manifolds and find no difference, then what would really matter would be underhood temperatures, that would of course be lower since the thermal barrier slows the passage of heat from the interior to exterior of the exhaust manifold, even though the surface temperature might be the same between the coated and uncoated manifolds.

Desiring to be thorough with the next opportunity to do this evaluation I assembled a few additional sensors so that I could check readings better.  On hand I now have an Infrared thermometer, an air temperature probe, a high temperature K-type thermocouple, and RS6 exhaust gas temperature sensors installed on my S4 to record the full range of exhaust gas temperatures.

I also have a stock set of exhaust manifolds currently installed on my S4 and a set of ceramic coated exhaust manifolds available for installation at my earliest convenience.

As a warm up for the more thorough testing I started my car with the air temperature probe placed 2.25″ from the exhaust manifold and took readings every minute with the Infrared thermometer to produce the chart below.

 I made some more readings the next day.