Airbox Minus Darintake Mod

One comment made to me regarding the findings about intake temperatures when applying foil to the airbox was that the Darintake modification will nullify any benefit that foil wrapping provides.  I have made this Darintake modification to my stock airbox as it allows more air through the airbox and on Stage 3 cars there can be sufficient airflow restriction in the stock airbox to cause the accordion hose to collapse if the modification is not performed.

Previously I have recorded temperatures on the pre-air filter side of the airbox with the Darintake holes covered and uncovered.  Those results indicated that the holes in the airbox could allow the pre-filter side of the airbox to warm more quickly than when the holes were blocked.  That finding does not necessarily prove that the pre-turbo air temperature is lower when the airbox is unmodified, it only suggests it might be.

With the current state of my S4 being set to take temperature readings it would be a trivial matter to block the holes I have made in the airbox and see what happens to the intake air temperatures.

Stock S4 lower airbox with Darintake Mod holes covered
Stock S4 lower airbox with Darintake Mod holes covered

So that’s what I did.  Out came the tape and I covered over the holes in the side and bottom of the airbox, limiting airflow through the airbox to the pure stock paths.

With the airbox sealed I made a set of drives along my daily commute route, one in the morning and one in the afternoon, recording the temperature inside the airbox post-air filter and in the inlet pipe prior to the turbochargers.

Results for the temperature rise in the airbox above the ambient air temperature are shown on the chart below for the morning drive:

Morning Airbox Temperature Delta with & without Darintake Modification
Morning Airbox Temperature Delta with & without Darintake Modification

Readings with the Darintake modification holes open are shown in Red and indicated in the Legend with +DI.  It’s clear that just past halfway in the drive the +DI temperature begins to rise faster for a couple of minutes before mirroring the -DI (no Darintake modification) temperatures.  The jump coincided with a longer delay at a stoplight in the +DI case.

These results give some support to the thought that the Darintake holes allow the intake air temperatures to rise more than with a stock airbox.  Looking at the temperature a little further down the intake path should make the picture clearer.  A comparison of pre-turbo intake air temperatures for the same drives is shown below.

Morning Inlet Air Temperature Delta
Morning Inlet Air Temperature Delta

Unlike inside the airbox, the temperature further along the intake path does not show a significant difference, in fact toward the end of the drive the temperature curves with the Darintake mod and without are essentially indistinguishable.

I also made readings during the afternoon drive which was warmer and also entails some longer stop and go driving during the first part of the drive.  Temperatures inside the airbox are shown below:

Afternoon Drive Airbox Temperature Delta
Afternoon Drive Airbox Temperature Delta

The drive in traffic meant there were delays that induced a shift in the time axis between the two data sets.  Being stuck at a light for a minute where the prior drive got through without stopping caused the rise of temperatures and subsequent fall as steady state driving was achieved, to occur at different points along the time axis.

The differences are less pronounced on this afternoon chart but it looks like the -DI case cools slightly faster under steady state driving and achieves about a 1-2 degree cooler steady state, although the +DI case had a slowdown that did not occur in the -DI case.

Again looking at the temperature pre-turbo:

Afternoon Inlet Temperature Delta
Afternoon Inlet Temperature Delta

As before the differences are very minor, the -DI case may cool a slight bit quicker once under steady state, but without taking more data the result is inconclusive.  Interestingly the temperature toward the end of the drive is higher in the -DI case, contradicting the theory that the Darintake holes allow warmer air into the intake.

Conclusion:

The addition of the Darintake holes may have some affect on the air temperature inside the airbox but the impact appears limited to the airbox and does not significantly affect the intake air temperature going into the turbocharger.

With additional drives and more tightly controlled conditions it may be possible to break out differences between the two configurations, but given the lack of clear performance differences over a couple of drives under similar conditions I believe it is safe to say that the Darintake modification does not affect the intake air temperature going into the turbocharger in a significant way.

Wrapped Airbox Summary

A few weeks ago I decided to put a roll of 3M Aerolite reflective film to use, this is a product that is similar to the DEI Reflect-A-Gold foil.

I took temperature measurements from a few locations on the B5 S4 intake, before and after the air filter inside the Airbox, inside the turbocharger inlet pipe that runs alongside the exhaust manifold, (on the side with the Airbox), and also the reading from the S4’s IAT sensor.

The question I was looking to answer: “does applying reflective foil to the exterior of the airbox lower intake air temperature?

I took three readings without any foil during my daily commute home to establish a baseline for the airbox performance.   On the final day I also recorded the temperatures on the drive in, which took place under cooler ambient conditions.

Then I applied the 3M Aerolite film to the exterior of the airbox.

Audi B5 S4 Airbox with 3M Aerolite Film
Audi B5 S4 Airbox with 3M Aerolite Film

Audi B5 S4 Airbox with 3M Aerolite Film

Audi B5 S4 Airbox with 3M Aerolite Film

As the pictures above show, I covered most, but not all the airbox.  I left the side that attaches to the vehicle body by the fender uncovered, as well as the back part of the underside that sits above the venting in the wheel-well liner.

My goal was to apply the reflective film in areas that are in line of sight with hot components to hopefully reduce the transfer of radiant heat.

With the airbox wrapped up I went back out to take “after” readings.

Wrapped Airbox Afternoon Drive Temperature Data
Wrapped Airbox Afternoon Drive Temperature Data

Shown above are the results from my “afternoon” drive.  The chart shows the temperature delta above ambient, that is, difference between the inlet pipe reading and the ambient air temperature.  Ambient air temperature is reported by the vehicle Outside Air Temperature sensor.  I found the vehicle sensor and my temperature probe to be 1 degree off from each other.

If the air temperature inside the airbox is being kept lower through use of the reflective foil it should be detected by the sensor that is downstream of the airbox.

A couple of things to note about the readings.  They were made over several  days so the driving conditions were varied.  Stoplight sequencing was a primary driver for the variance in rate of temperature change, but ambient temperature played a part as well. On cooler days the temperature rise was less pronounced.

On the chart above the two blue lines are the results with the foil applied.  These reading are also indicated by an asterisk * in the legend.

Shown below are results from the morning drives, again with foil applied drives indicated with the asterisked * name in the legend.

Wrapped Airbox Morning Drive Temperature Data
Wrapped Airbox Morning Drive Temperature Data

Because the commute is from a suburb into the city steady state speed is maintained in the first part of the morning drive, with stop and go actions cropping up toward the later part of the drive.

This is reversed in the afternoon drive, where stop and go driving is predominant early in the drive, and then steady state driving is observed later in the drive.

Conclusion:

There does not appear to be much influence on the inlet air temperature as a result of applying the 3M Aerolite foil.

This test does not take place under the exact same temperature conditions, with the exact same amount of time spent at stop lights, or at the exact same speed at specified times during the drive.

On the other hand, if the foil made a difference one would hope it would be evident from typical driving patterns.  Most telling is the temperature data toward the last couple of minutes of the drives. After roughly 30 minutes (1800 seconds) of driving the temperature above ambient is within 2-3 degrees  and the temperature lines become difficult to distinguish as they bunch together.

Audi B5 S4