Recently I’ve been logging pressure at the compressor housing and prior to the throttle body.  I’ve noticed that the stock sensor, before the throttle body, has been reading higher, which it should not.  I’ve switched to a Dwyer pressure sensor to try and eliminate quality issues with the sensor, but it was still reading a bit lower than the stock sensor.

I next thought that perhaps with the sensor plumbed in prior to the N75 valve that maybe some pressure was being bled off by the N75 valve.  To eliminate that possibility I ran one compressor line to the N75 and the other to the pressure sensor.  Still the pressure from the Dwyer sensor at the turbo was less that the pre-TB pressure.

That led me to question if the stock MAP sensor is reading correctly.  I’ve got two extra MAP sensors in the toolbox, one new and the other used.  I thought that if I hooked the sensors up to an air compressor and ran the pressure up to 20 psi I could log with VCDS the boost pressure being reported to the ECU.

I hooked up the contraption below to record these MAP sensor readings:

This is a pressure regulator normally used to perform leak down testing running into the MAP sensor which is electrically connected to the car.

As I turned the pressure up VCDS reported the increase in millbars until the reading reached 1300 mbar and then it stopped rising.  I thought perhaps without the engine running there wasn’t enough juice going to the sensor, so I started the car and tried again.  This time pressure stopped at 1390 mbar.

Apparently the car is limited on how much boost it will read if the boost is not being developed as expected.  So much for this idea, I’ll need to log the different MAP sensors on the road and see how they compare.

I previously installed a pressure sensor on the intake pipe to the passenger side turbocharger, and today I added a sensor to the driver side downpipe.

Then I wired up the pair of sensors to the Innovate LMA-3 Aux Box to record pressure drop prior to the K03 turbocharger compressor, and exhaust back pressure prior to the catalytic converter.

The exhaust system is the 034 Motorsport 3.5″ single with catalytic converters.  On the intake side I am using a paper filter in the stock airbox with some holes made in the lower half of the box, a stock S4 MAF housing, accordion hose, and y-pipe.  The turbo inlet pipes are TiAL 2.25″ stainless steel.

Testing was done over a full second gear and third gear pull with an additional third gear pull part way through the rpm range.

The results are shown below.  On the top half of the chart is the exhaust back pressure and the lower part of the chart is the pressure drop leading into the turbo.

While these results are with the BorgWarner K03 turbochargers, the S4’s stock components, I am still pleased at the minimal pressure drop through the exhaust system.

As a follow on test I may install the RS4 airbox top, RS4 MAF housing, RS4 accordion hose, and RS4 y-pipe to see if any different pressure drop results are seen with that different intake system.

Today I made some more readings of the surface temperature of the driver side exhaust manifold from engine start through ten minutes total time.

I’m using a Craftsman IR temperature sensor to record the surface temperature of the exhaust manifold.  This time the exhaust manifolds on the car have a black thermal barrier coating on them, as shown in the picture below.

The ambient air temperature was about 20 degrees cooler today than when I made the previous recordings.

I have also noticed that where the IR sensor is pointed can affect the reading a good amount.  To try and minimize the affect on the results I picked a marking on the surface of the exhaust manifold to point the temperature sensors laser pointer at each time.

Below are the results from the previous testing with the latest results added on.

I am a bit surprised by how much less the temperatures recorded on the coated exhaust manifolds were.  The only apparent differences aside from the coating was the ambient temperature, but I would not expect it to have such a strong influence on the exhaust manifold surface temperature.  Ideally I would be able to log under the same ambient temperature conditions, but given the time of year that it is now it is unlikely that temperature conditions will be equivalent in the near future.

The other question I have is to how well these results would carry over to a longer period of time, when the car has been operating with a load on the engine.  This experiment only spanned ten minutes and was done entirely with the engine idling.