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The test vehicle was the Novak Subaru GC8 time attack car raced by our own Project 370Z owner Clint Boisdeau. Ideally, the thermocouples would be installed in the airflow. However, as this was a hair-brained idea I came up with less than a week before the car was to go testing (and I didn’t even own a portable thermocouple data logger at the time), we didn’t have time to do the ideal test setup of plumbing the thermocouples into the charge pipes before and after the intercooler. So what did we do? We placed the thermocouples on the outside of the charge pipes.
Of course, this introduces some error into the calculations. Why? The temperatures we measured at the outer surface of the charge pipes depended on the physical properties of the aluminum charge pipes as the heat has to transfer from the charge air through the pipe before it gets to the outer surface. All materials have a level of thermal conductivity, or said another way, a resistance to transferring heat. Aluminum has a high thermal conductivity (or low resistance to preventing heat transfer), so we’ll ignore it. The mass of whatever you’re trying to transfer heat through has a capacitance that creates a time lag from when the heat enters one side of the material and exits the other. The aluminum pipes are thin wall, so we’ll ignore capacitance too. But just remember the thermal resistance and capacitance will alter our measurements a bit from the actual temperatures in the pipes. As a side note, you can model heat conduction like an electrical circuit with the aluminum pipe acting like a resistor and a capacitor. Because aluminum is a good conductor and the pipe is thin-walled, it’s like a small resistor and small capacitor.
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The thermocouple measuring the charge air temperature after the intercooler was placed about halfway between intercooler exit and the throttle body. As the thermocouple is not located directly at the intercooler exit (note to self, buy thermocouples with longer wires), there is some error introduced as some heat could have transferred into the pipe coming from the hot air off the radiator.
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The location of the thermocouple measuring the charge air temperature before the intercooler is about halfway between the intercooler and turbocharger (yeah, not at the intercooler either). This also introduces some error as there is probably some heat loss from the charge air before it gets to the intercooler.
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The thermocouple measuring the ambient air temperature was chillin’ in a gap in the bodywork between the bumper and headlight.
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The final thermocouple was jammed into the air filter.
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