Continuing my investigation (first post here) into how the air filter temperature changes under different driving conditions I recorded my morning and afternoon commutes.  Note that the temperature readings appear to drop below the ambient temperature, this is likely due to a combination of factors, such as the temperature sensor having some variation, me not monitoring the temperature on the dashboard closely, and driving through cooler pockets of air.

Morning:

and in the early evening/late afternoon:

I’m now wondering more about those holes in the airbox:

I’m curious now to know if they are letting hot air into the airbox more readily than would a closed airbox. To test this theory out I went and unmodified the bottom half of my airbox, shown below:

The plan is to drive the car tomorrow along a similar route and see how the temperatures compare.

Below is a close up of the temperature sensor probe as it is positioned inside the stock air filter.

The follow on observations are here.

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.