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Many modern factory turbocharged vehicles come equipped with a with an “Air to Air” heat exchanger (IE: Intercooler). This heat exchanger can be made up of a “Tube and Fin” or “Bar and Plate” core placed in the charged air stream of the intake piping exiting the turbos’ compressor housing, and utilizes ambient temperature air flow to cool the charged air. The objective of this testing is to compare four different designs that may each have a best fit for different applications or uses on the same car, as the test will focus on the 2015+ Subaru WRX with a top mounted (Above the engine) heat exchanger as equipped from the factory.

The 2015 Subaru WRX comes equipped with the FA20DIT Direct injected, turbocharged, 2.0L Flat-4. Under OEM conditions and power levels these factory heat exchangers are able to sufficiently cool the air, but once modified they will no longer be up to the task. As both air flow, and air temp increase with more boost, larger turbos, and strenuous use, the factory heat exchangers are no longer able to keep up with the demand. In this paper we will test four different aftermarket heat exchangers from a range of manufacturers (MAP, Brand X, Brand Y, Brand Z).

Design will vary from core size, core density, end tank design, and end tank materials. The testing was performed on our in house Dynojet Dynamometer, and the variables logged were Inlet air temperatures (F), Outlet air temperatures (F), Inlet air pressures (PSI), and Outlet air pressures (PSI). The test vehicle made two consecutive logged pulls after operating temperatures where reached. We will use the data gathered to explain where each heat exchanger will see its most efficient use.

The Model

Test Conditions:
  • Test Vehicle - 2016 Subaru WRX - MAP Stage 2 Spec, MAP Charge Pipe
  • 93 Octane Fuel
  • Tune was not changed between runs
  • Dynojet Dynamometer 424x
Heat Exchangers Tested (bottom of page):

  • Test Vehicle - 2016 Subaru WRX - MAP Stage 2 Spec, MAP Charge Pipe
  • MAP - Bar & Plate core, billet end tanks, Lower density finpacks Core Size: 14”x 10”x 3.5”
  • Grimmspeed - Bar & Plate core, cast end tanks, high density internal and external finpacks. Core Size: 13”x 10”x 3.75”
  • Mishimoto - Bar & Plate Core, cast end tanks, medium density finpacks and highest number of rows per inch. Significantly larger core than rest. Core Size: 15”x 10”x 4”
  • TurboXS - Bar & Plate core, cast end tanks, low density finpacks. Core Size: 13”x 10”x 4”

Pressure Delta & Hydraulic Efficiency
When speaking about the pressure delta’s and the hydraulic efficiency of a heat exchanger (IE: intercooler) what we are referring to is the pressure drop across the core, and the rise, or fall of needed effort to move air through it. We measured the pressure delta on each heat exchanger by utilizing a pressure transducer on the inlet, and the outlet, and we measured the hydraulic efficiency of each design by monitoring the wastegate duty cycle needed to maintain the target boost level in the intake manifold at 6000RPM.

Why do these points matter? By looking at the pressure delta, and the Hydraulic efficiency of each we are able to see how much harder the turbocharger will be working to achieve the same target boost level for each core. Think of it as the path of least resistance, the easier it is to pass the air though the heat exchanger, the less work the turbo will have to do, as the harder it works the more heat it will produce. Adversely, although less resistance is theoretically ideal, the result may be that the air is not sufficiently cooled during its time in the heat exchanger as it is not able to transfer the heat out.

In many cases people see pressure drop and attribute that to a bad design, when in fact there will always be some drop with an effective heat exchanger. As when the air cools, the pressure will drop in relation to that, and not just based off the resistance in the core. Along with the fact that as you add more cooling capacity, such as a larger fin density, you will inherently be increasing pressure drop across the core. When the ability to pull more heat from the air increases, the release of energy is going to lower the pressure and decrease the perceived hydraulic efficiency.

What we found was that all four heat exchangers are actually very close to each other when looking at Hydraulic Efficiency (Data based on Wastegate Duty Cycle at 6000RPM) as the high and low are only separated by a 4.5% difference, and although a slightly larger gap the same goes for the Pressure Delta between them all. Based on average pressure drop (Percentage of Inlet PSI after 3000rpm) the difference between the four was only 4.08% between the high and the low when the two runs were averaged.

graph 1
The Graph above illustrates the pressure drop of each heat exchanger, based on the percentage of Inlet pressure (PSI) VS Outlet pressure (PSI). Data is an average of two runs completed consecutively for each heat exchanger.
Average Pressure Delta Between Inlet and Outlet:
  • TurboXS - 2.47%
  • MAP - 3.99%
  • Grimmspeed - 5.20%
  • Mishimoto - 6.55%
graph 2

The Graph above illustrates the wastegate duty cycle at 6000rpm, this data is used to calculate hydraulic efficiency of each. Data is an average of two runs completed consecutively for each heat exchanger. Hydraulic Efficiency Based on Wastegate Duty Cycle at 6000 RPM:
  • TurboXS - 38%
  • MAP - 41%
  • Grimmspeed - 41.5%
  • Mishimoto - 42.5%
Temperature Delta

As with any heat exchanger, the main objective of the four that we tested is to lower the temperatures of the air charge exiting the turbocharger and entering the throttle body of the engine. The lower the air charge temperature is the more dense it will be, allowing more air and fuel to enter the combustion chamber, thus more available and efficient power.

The cooling efficiency test was conducted over a course of the same dyno runs which all had equal starting coolant temp, ambient temp, IC Inlet temp, and Pre-Turbo inlet temp, and with equal time cool-down time between runs. The data below shows the delta at the end of the run charge air temp versus the beginning of the run comparing inlet and outlet temps of the heat exchanger. What we found was that the larger and significantly more dense core size of the Mishimoto allowed it to really shine in this test. With not only a lower outlet temp after the first run, but it was less prone to heat soak and kept the second run much cooler for both inlet and outlet temps compared to the other three.

The MAP and the Grimmspeed coolers were nearly identical, within three degrees on both second runs. Both showed a small sign of heat soak as the outlet temps rose on the second runs compared to the first. The TurboXS cooler was the worst of the bunch when it came to dropping intake temperatures, as it was consistently ten or more degrees hotter on both runs.

  • Run 1
  • Inlet temp beginning of run: 106F - Outlet temp at beginning of run: 91F
  • Inlet temp end of run: 238F - Outlet temp at end of run: 94F
  • Run 2
  • Inlet temp beginning of run: 118F - Outlet temp at beginning of run: 95F
  • Inlet temp end of run: 246F - Outlet temp at end of run: 96F
  • Run 1
  • Inlet temp beginning of run: 104F - Outlet temp at beginning of run: 90F
  • Inlet temp end of run: 230F - Outlet temp at end of run: 95F
  • Run 2
  • Inlet temp beginning of run: 149F - Outlet temp at beginning of run: 94F
  • Inlet temp end of run: 256F - Outlet temp at end of run: 106F
  • Run 1
  • Inlet temp beginning of run: 104F - Outlet temp at beginning of run: 90F
  • Inlet temp end of run: 239F - Outlet temp at end of run: 96F
  • Run 2
  • Inlet temp beginning of run: 125F - Outlet temp at beginning of run: 98F
  • Inlet temp end of run: 250F - Outlet temp at end of run: 106F
  • Run 1
  • Inlet temp beginning of run: 106F - Outlet temp at beginning of run: 92F
  • Inlet temp end of run: 242F - Outlet temp at end of run: 120F
  • Run 2
  • Inlet temp beginning of run: 128F - Outlet temp at beginning of run: 97F
  • Inlet temp end of run: 250F - Outlet temp at end of run: 128F


From the data points we have gathered, we can conclude a few things from this testing. MAP, Grimmspeed, and Mishimoto were all nearly identical when it came to horsepower numbers produced. Mishimoto with its larger core brings more cooling capacity to the table than any of the other units with only a slightly larger drop in hydraulic efficiency.

The downside to their cooler size is that it requires a decent amount of trimming and massaging to make fit, along with some aftermarket piping that is required, which results in it being not 100% truly factory bolt in. Because of this, the small gains we see may not be worth it to the average customer. Where this heat exchanger will shine is the higher heat, more prone to heat soak environments such as road racing, or customers in the southwest USA. The MAP heat exchanger, and the Grimmspeed unit will be the two that we would put as near equals, these coolers will both shine in the “Daily Driver” market of cars with standard bolt on modifications, or even upgraded turbochargers, but with the size of the cars they may still be prone to some heat soak in high heat or high stress environments.
The small variances could be attributed to the Dynamometer in most cases and are well within an acceptable range to say so. TurboXS would be the heat exchanger we would not really put in any markets looking for performance, as its ability to cool was much worse than the rest, and consistently made 5-7 less horsepower each run.

This unit would work in a very cold environment that would have no issues with heat soak. What is important to take away from this is that when looking for an intercooler for your core, there will be more than one thing to consider. All too often we see recommendations being made on a single data point that may not take everything into consideration. What may be best for one car build, may not work at all on the next.

About Modern Automotive Performance

Established in 2006, Modern Automotive performance is a world class manufacturer and eCommerce business focused on the Automotive Aftermarket. With a focus of technology and efficiency implementation on our manufacturing side, and a strong customer focus on our eCommerce side we are one of the fastest growing business in our segment. With in house CNC capabilities, full fabrication and R&D facility, and in house Dynamometer at our 50,000sq ft Cottage Grove, Minnesota facility. We are equipped to handle any needs we face.

Technical Break Down of Each Heat Exchanger

Tech breakdown

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