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Juni 2, 2020

Intercooler Sizing And End Tank Design With Rob Dahm

Rob Dahm rethinks, redesigns, and retests his current intercooler and end tanks to unlock more horsepower on his 4 rotor RX7. Using CFD analysis, he identifies where the current setup has restrictions that are causing pressure drop and robbing Rob’s 4 Rotor of horsepower. The goal of a well designed intercooler and end tank set up is to have consistent flow through the tanks and core to optimize cooling and also minimize pressure drop. Pressure drop is when the pressure leaving the core is lower than what is coming in from the turbo due to restrictions in the design. See Robs latest video that details his process.


System Optimization

On the Garrett website you can find some important information on turbo system optimization. Click here for the whole writeup or read on below for information on intercooler systems.

Each intercooler core is rated for a specific horsepower, making it as easy as matching your desired power target to the core. In general, use the largest core that will fit within the packaging constraints of the application. Click here for our intercooler product page. 

The piping diameter should be sized with the capability to flow approximately 200 – 300 ft/sec. Selecting a flow diameter less than the calculated value results in a pressure dropping due to the restricted flow area. If the diameter is instead increased above the calculated value, the cooling flow expands to fill the larger diameter, which slows the transient response. For bends in the tubing, a good design standard is to size the bend radius so it is 1.5 times greater than the tubing diameter. The flow area must be free of restrictive elements such as sharp transitions in size or configuration.

Calculating Flow Area: π x Radius² 

For Example:
GTX5533R Gen II has a 3.25″ compressor outlet diameter

3.25 / 2 = 1.625 (Radius)
π x 1.625² = 8.30 inches²
Intercooler ducting is 3″
3 / 2 = 1.5 (Radius)
π x 1.5² = 7.07 inches² 

Conclusion:  In the scenario above you can see the area of the compressor housing outlet is 8.30 in² and the area of the intercooler ducting is 7.07 in²  even though there is only a .25″ difference in the radius. This will result in a restriction in the intercooler system and a potential loss in performance. In very simple terms, be aware that ducting for your turbo system should never be smaller than the radius of the compressor outlet or outlets in twin systems.

Another important factor in selecting the correct intercooler is the end tank design. Proper manifold shape is critical in minimizing pressure drop and providing uniform flow distribution. Good manifold shapes minimize losses and provide fairly even flow distribution. The over-the-top design can starve the top tubes, however. The side entry is ideal for both pressure drop and flow distribution, but it is usually not possible due to vehicle space limitations. Proper mounting of the intercooler increases the durability of the system. Air to air charge air coolers are typically “soft-mounted”, meaning they use rubber isolation grommets. This type of mounting is also used for the entire cooling module. The design guards against vibration failure by providing damping of vibration loads. It also reduces thermal loads by providing for thermal expansion.

For example:
Tubing Diameter: velocity of 200 – 300 ft/sec is desirable.
Too small a diameter will increase pressure drop, too large can slow transient response.

Velocity (ft/min) = Volumetric Flow rate (CFM) / Area (ft2)
For twin turbo setups, divide the flow rate by (2).

Charge tubing design affects the overall performance, so there are a few points to keep in mind to get the best performance from your system.
Duct bend radius: – Radius/diameter > 1.5
Flow area: – Avoid area changes, sharp transitions, shape changes. Available packaging space in the vehicle usually dictates certain designs


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