Category Archives: Testing

Cruising Turbo Outlet Temperatures

I reattached the temperature sensor that I use to record the compressor outlet temperatures.  Combined with the readings from the inlet temperature sensor these two pieces of data illustrate the rise in intake air temperature that occurs as the air passes through the turbocharger compressor.

This sensor is located in the hard pipe that joins the turbocharger compressor outlet to the intercooler intake end tank.

Auber Instruments Air Intake Temperature Sensor
Auber Air Temperature Sensor installed in charge pipe joining turbo and intercooler

As I have done for the past couple of weeks I logged the temperature of the intake air as it passes through the car’s intake system.  The results from the morning drive are shown below:

Morning Drive Temperature with Turbocharger Outlet Temps
Morning Drive Temperature with Turbocharger Outlet Temps

Tu_In is the temperature of the air entering the turbocharger, shown with the red line.  Tu_Out, the dark green line, is the temperature of the air as it leaves the turbocharger compressor housing.  The light green line is the ambient air temperature.  Interestingly the turbocharger outlet temperature goes well above the intake air temperature at the Intake Manifold within about 2 minutes of starting the engine.

What is also noteworthy is that at no time did I push the turbo’s to produce boost, the spikes occurred while the intake manifold was still under a small amount of vacuum, as displayed by my A-pillar mounted boost gauge.

SPP A-Pillar Gauge Pod
SPP A-Pillar Gauge Pod

I recorded temperatures again during  an afternoon drive, though the route was different from what I have previously taken.

Afternoon Drive recording Turbo Outlet Temperatures
Afternoon Drive recording Turbo Outlet Temperatures

I briefly pushed the turbochargers to produce boost of approximately 18 psi during the end part of the drive.  This boost event only lasted around 1-2 seconds.  I would have expected to see compressor outlet temperatures around 250 degF or greater if sustained boost around 20-22 psi had been achieved for 3-4 seconds.

One of the most notable aspects of these charts is the delta between the green, compressor outlet, and red, compressor inlet, temperatures.  This is the rise in intake air temperature as the air passes through the turbocharger compressor, a large change results even when out of boost and only cruising.

Gold Wrapped MAF Sensor Housing

Continuing down the intake, I wrapped the MAF sensor housing with the DEI Gold tape, and put a double layer of heavy duty aluminum foil around the accordion hose.

DEI Gold Wrapped MAF Sensor Housing
DEI Gold Wrapped MAF Sensor Housing
Kingsford Aluminum Foil

One theory has postulated that the location of the MAF sensor housing above the passenger side turbocharger means that “all of the hot air coming from the turbocharger will rise and heat up the MAF sensor housing”.

Perhaps, this step was an attempt to see if wrapping the MAF sensor housing and accordion hose would lead to a temperature reduction at the inlet pipe.

Here’s the morning drive results:

Morning Drive with MAF Sensor Housing Gold Wrapped
Morning Drive with MAF Sensor Housing Gold Wrapped

The dark blue line is the data with the MAF sensor housing wrapped in the DEI Gold tape.  It (Gold tape and Aluminum foil) does not appear to have significantly altered the temperature profile.

In the afternoon the results were:

Afternoon Drive with DEI Gold tape on MAF Sensor housing
Afternoon Drive with DEI Gold tape on MAF Sensor housing

Again there was nothing notable in the results to indicate that the DEI Gold tape applied to the MAF Sensor housing led to a reduction in the inlet air temperatures.  This drive took place on one of the hottest days yet, thus the temperature curve is higher than most others.

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.