Tag Archives: Monitoring IAT2

Datalog analysis of Cadillac STS-V Ambient vs IAT1 vs IAT2

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I have been planning new data-logging experiments and modifications, so I have been reviewing the datalogs I did last August in the summer temperatures.  For my next datalog I will attempt to capture comparative data to this info:

This screen is an HP Tuners VCM Scanner guage snapshot of parameters after a 0-60 run culminating at 65 mph.

Baseline from August



MPH (Temps in Deg Fahrenheit)

Item 0 30 45 60
Ambient 90 90 90 90
IAT1 113 117 113 106
IAT2 118 120 127 135
MAT 120 121 136 169

What we can see from this table, is that at the beginning of the 0-60 run the Ambient temp is 90F, and stays at 90F through the run.

IAT1: The IAT1, which is incoming air temperature as read in the intake air tubing, starts at 113F.  It has rapidly gone up to this value because the STS-V is stopped.  However, as the V accelerates to 30 mph it rises to 117F.   By 45 mph it has returned to 113F, and by 60 mph due to the incoming 90F air cooling it has resolved to 106F.  Conclusion:  heating of the incoming air at the IAT1 sensor does in fact effect the air temperature, and thus performance.   Conventional wisdom is that the incoming air is not in the intake tube long enough to become heated. Net Rise: -7F

IAT2: The IAT2, which is air after it has been heated by the supercharger and cooled by the intercooler, starts at 118F, a 5F increment over IAT1.  By 30 mph it has risen to 120F.  At 45 mph it has risen further to 127F, and by 60 mph has peaked at 135F.  Net rise: +17F.  Keeping in mind the IAT1 went down 7F in this time.

MAT: The manifold air temperature is a calculated value the engine uses to predict the temperature of air in the manifold.  It tends to go up at a higher rate than IAT2.  The MAT starts the run at 120F, is about the same at 30 mph at 121F, but rises to 136F by 45 mph and on to 169F by 60 mph.  Improvements in the IAT2 should have even greater improvements in the MAT value.  Net rise: +49F.

As a result of the high MAT temp by 65 mph as shown in the image, IAT temps are causing 3.6 degrees of advance to be pulled.  This begins at 59 mph when the IAT2 hits 135F and the MAT is at 157F at -3.2 degrees.
This was a video capture of the dashboard of the 0-60 run from August:

Monitoring IAT, IAT2 Cadillac STS-V

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This morning I did some data-logging with HPTuners up and down the highway.  I am still learning the software, so feel free to make suggestions.

I grabbed these screen shots of a couple of points: (click on the image for a zoom-in version, then hit back to come back):

HPTuners datalog screenshot 1

What the first screenshot shows is that at 69 mph and 6651 RPM the supercharger was making 10.7 psi.  During this portion of the run, ambient air temperature was 90F, IAT air coming into the MAF temperature sensor was 108F, and IAT2 air leaving the intercooler was at 151F.

Actually I would have expected the car to shift at 6500 rpm, but 6651 is close enough I suppose.

In the chart display at the bottom however, you can see that the IAT2 was already elevated before the higher-RPM event occurs.

The question for today though is how the IAT2 151F compares with ambient air 90F.  The Supercharger adds heat to the intake air in the process of compressing it.  At maximum RPM as here, the Supercharger is spinning at 2.1:1 and so 13,967 rpm.   This can add up to 200F to the air coming into the intercooler.   Today the air coming in to the supercharger was already 108F, so heating it by a couple hundred degrees puts some very hot air across the Laminova intercooler tubes. The goal for the Intercooler is to reduce the heated air back as close to ambient air as possible, pulling the air back from 200F+ down to 151F in this example.  The unachievable ideal is that the intercooler get the air down to the intercooler heat exchanger’s own cooling source, which is the ambient air coming into the front grill at 90F.

HP Tuners datalog screen shot 2

In the second screen shot, at 39 mph and 6502 rpm, ambient air was 88F, MAF intake air 108F, and IAT2 after the supercharger was 135F.

On a separate topic, long term fuel trims appear to be small, which I think is good.

Points to ponder:

How to reduce the IAT2 temperatures from 151F when accelerating at highway speeds

Why the max pressure seen was 10.7 psi instead of 12 psi?  Is this also temperature related?

How will these readings change in cool air?