AEM Temperature Testing Procedures

AEM Temperature Testing Procedures
AEM performs temperature testing to ensure the creation of the most useable power in real-world driving conditions.

We use thermocouples and an ECU scanning tool to monitor and record temperatures along the inlet path, under the hood, and outside of the vehicle. The scan tool is used to monitor inlet air temps at the IAT sensor, coolant temps at the CLT sensor, and basically everything that the ECU sees from the factory sensors to determine which fuel and spark calibrations it should use. Once the vehicle is at normal operating temperature, it is subjected to a battery of driving simulations (slow cruising, stop and go, hard acceleration, highway speeds and abrupt stop after cruise) and all of the data from the thermocouples and scan tool is recorded. Through the acquisition of this information, we are able to replicate these conditions during our dyno testing to produce a realistic average power gain.

On some vehicles, the tuning effects of the system do not allow us to place the inlet air source outside of the engine compartment, as evidenced by certain Short Ram and Dual Chamber applications. In these instances, we also use temperature testing to determine the best location for the inlet source in addition to the standard temperature testing that is performed during the development phase.

To understand how inlet air temperatures affect performance, AEM engineer Damon Riggs provides a discussion below:

The international standard for an internal combustion engine atmospheric correction factor is given by the Society of Automotive Engineers (SAE J1349 Reaffirmed June 1995). The simplified equation is as follows:

International Standard for Internal Combustion Engine Atmospheric Correction Factor


Bdo = Measured inlet air supply dry air pressure (inHg)

to = Measured inlet air supply temperature (°F)

Once a correction factor (CF) is determined, corrected horsepower is calculated by multiplying the CF by the measured horsepower.

Let's look at the following example:

A typical 2002 Honda Civic Si equipped with an AEM Cold Air System puts down 141.6 measured horsepower on a 77°F day at sea level when the atmospheric dry air pressure is 29.235 inHg. These are the SAE standard testing conditions, therefore the CF = 1. In this environment, the corrected power is equal to the measured power.

Now let's take this car out to the desert where the temperature is 97°F and the dry air pressure is still at 29.235 inHg. Using the above equation, the CF is determined to be 1.022. A CF of 1.022 is telling us that in these conditions, this car will output only 97.8% of the horsepower that would otherwise be measured under SAE standard testing conditions. To determine the power that the Civic will actually put to the ground, we divide the corrected power by the CF. Therefore, if we dyno the Civic in these conditions, the dyno will measure 138.6 hp at the wheels. That is a 3.0 hp loss, or 2.1%. The corrected power will be the same, though, 141.6 hp.

If we take the Civic where it is cooler (57°F) and the dry air pressure is the same as that of the desert, the CF is 0.978. This CF tells us that at this location, 2.2% more power will actually be achieved when compared with the power output at the SAE standard testing location. An uncorrected dyno run here will record 144.8 hp. That's over a 2.2% increase or 3.2 hp.

In each of these three testing conditions, the corrected power is the same. This is due to the use of a standardized correction factor and it allows us to accurately compare dyno runs taken in different environments. Nearly every dyno run that is published displays corrected power. The fact that a correction factor like this is required reveals the importance of inlet temperatures on power output. Cooler intake air ultimately makes more power. This is part of the theory behind the design of AEM Air Induction Systems.