Air Masses Flow From What Pressure To What Pressure Intercoolers – Explained

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Intercoolers – Explained

Engine performance parts improve supercharger performance…

I am compiling a guide for information on how to select the correct engine performance parts to meet your target power requirements. Basically I want to take all the guesswork out of tuning and save you some money from doing things over and over again.

I was honestly lost when researching ‘to buy the right intercooler’. There you will find two types of information:

1-A class article written by engineers about pressure differential, thermal efficiency, enthalpy, and multi-variable equations that are even remotely related to flow, horsepower, torque, supercharger rpm, or anything else we can use as input. to our equations. (Basically this science needs to be translated into layman’s terms)

2-The other category is a bunch of random trial and error advice by enthusiasts, press releases, and other stuff you find online.

Here’s what we know:

First let’s talk about how intercoolers work. There is some debate as to whether the intercooler is more like a heat sink whose function is to absorb thermal energy from the incoming air to prevent heat from reaching the engine, or whether the intercooler is more like a radiator, where air flows over the intercooler. Responsible for removing heat from the inlet air charge.

The correct answer is both are correct…

Air flowing through the intercooler spends very little time inside the intercooler and slowing down for more thermal exchange (like we would with coolant in a radiator) prevents air from reaching the engine which is a restriction on power. Because the air spends some time in the intercooler, the intercooler typically has multiple passages, internal ribs, and fins inside it to increase the surface area contact between the intercooler aluminum and the compressed air molecules. In this sense, the total volume of the intercooler and the total area of ​​its internal surfaces are like a heat sink that absorbs heat energy from the compressed air. In this aspect it makes sense that the bigger our intercooler the better. Furthermore, this also means that the more complex and intricate the internal passages of our core, the more heat we can extract from the charge air. The flipside of this of course is that very complex internal passages can create turbulence and restrict airflow so ultimately there is a good design balance between internal complexity and flow capacity.

When we start, the intercooler is cold, and on your first power up, as the hot compressed air runs through the intercooler, the heat is transferred to your heat sink (which is the intercooler) and nice cool air is released to enter. After the engine is first run, the intercooler is warm; And if we want to run another power back and forth, the intercooler won’t be able to sink much heat because it’s already somewhat warmed up. Here comes the intercooler as a radiator, the heat transferred from the air to the core of the intercooler must be removed either by cross-flowing air into the air intercooler or by cooling the air fluid in water. intercooler, or even through an ice water bath for drag racing applications. Without the intercooler removing the heat it has absorbed from the compressed air, the intercooler will heat up after the run until its temperature matches the temperature the compressed air is heating. At this point there is no temperature difference between the air and the intercooler core and we can no longer sink any more heat.

Some cars have their intercooler under the hood of the car (such as the Mazda Sentia / 626). In this type of installation the intercooler is mainly a heat sink and will be used for a few passes until it is wet, once it is wet it must be left to cool until it returns to hood temperature before it can be effective as an intercooler again. . From this we assume that any intercooler, no matter how small, or poorly maintained, is better than an intercooler because it increases potential horsepower, at least for that first power run.

Now I want you to keep this information in mind as we talk about the dimensions of the intercooler…

An intercooler has three main dimensions, height (H), width (W) and depth (D), and based on that there are some physical concepts we want to consider:

Cross Sectional Area:

Height x depth = cross section of the intercooler and is related to how well the intercooler will flow and whether it restricts the intake flow. This is the surface area that faces the compressed air as it travels through the intercooler. Like free flowing intakes, throttle bodies and exhausts, if this area is undersized it will restrict flow and reduce performance.

Width:

Width = length of intercooler and if you have same side inlet/outlet intercooler then your intercooler length is effectively 2*W. Air has to pass through this gap through a turbulent and complex intercooler core. The longer this length, the greater the pressure drop across the intercooler, so a wider intercooler is not advisable as the turbocharger compression will be wasted in the intercooler pressure drop, and having a single side inlet/outlet is also not advisable. Intercooler where the air has to travel a long distance to the core.

Front:

Width x Height = The front of the intercooler that faces the incoming ambient air A well sized front area (like a radiator) is needed to ensure the intercooler doesn’t overheat and that the fast incoming air flow is able to efficiently cool the intercooler if you run back to back power. can do As we increase this area, we expect the intercooler to have better control of its maximum operating temperature and better repeatability no matter how long we stay in boost (good for mile races or all-day road racing events, for example).

room:

Room = the room of the intercooler, usually the intercooler is mounted in front of the radiator… if you increase the room too much (and especially without adding proper air to the intercooler and the airfoil between the intercooler and the radiator) you slow down the incoming ambient air enough that your radiator starts to overheat. So increasing D gives us better intercooler efficiency and more flow capacity (H*D is the cross sectional area mentioned above) but it reduces engine cooling efficiency so it should also be controlled.

Last but not least:

Total volume:

Height x width x depth = total volume of the intercooler, which is an indirect measure of the internal surface area of ​​the intercooler. The bigger the volume, the bigger the heat exchange surface area, the more heat we can get out of the air in a very short period of time (100 milliseconds or the air spends inside the core). Obviously the larger the volume the better the cooling and the worse the pressure drop. Again this number needs to be controlled.

How do I know if the intercooler I have now is adequate?

Intercooler performance can be checked in two ways:

1-Thermal performance

a. Measure the temperature difference between the intercooler inlet air and the intercooler outlet air and use this delta T to compare the intercoolers available to you. The best intercoolers out there can lower the air temperature by over 100*F and get you within 20* of the ambient air temperature. If your factory intercooler can already achieve the same results, there is no need to upgrade.

b. Track your intercooler temperature in long power runs or back to back power runs. The design and placement of the intercooler should be sufficient to control the temperature rise over time (ie 60+ mph air hitting the intercooler), if the temperature rise is too high you may need a better ‘radiating’ core. Frontal area, better air guides and air foils, and better placement with high pressure air in front and low pressure air behind…we’ll explain more about this later.

2-stream performance

a.Measure 28″ of water flow through the intercooler core (standard for most flow meters), or measure the total intercooler pressure drop at the flow rate required for your target horsepower. If the intercooler is on the car, measure the difference between peak HP figures and the pressure across your intercooler.

The best intercoolers will have a pressure drop of less than 1psi (typically 0.5 to 0.9psi) at peak boost and horsepower. If your intercooler is within these power figures, there is probably no need to upgrade.

Now going back to choosing the best sized intercooler for your application, it would be very difficult for me to find the exact math on how to optimize your intercooler size and then translate that math into ‘car terms’ of power. , inlet air temps, supercharger outlet temps, pressure ratio and boost pressure…etc.

Here is another solution; One thing engineers like to do when faced with a problem is to plot statistical data on charts and find some trends…

I found about 30 different intercoolers online with flow tests (CFM), or dyno tests (HP), or both, and we know that it takes roughly 1.5 CFM of air to produce 1 HP (depending on density), so I put both sets together. Data from both flow tested OEM intercoolers and aftermarket ‘engineered’ intercoolers to create the graph below:

Flow in CFM vs Cross Sectional Area Trends: 

Flow (CFM) = 11.63 * Cross Sectional Area (Square Inches) – 12.84

Here is a plot of flow in CFM (vertical) vs cross sectional area (square inches) for the 30 cores I have data for. As you can see there is a linear relationship between current and area which is expected. So we can use this as a guideline to figure out the available core (for a given depth D), the minimum height of our intercooler to get good flow efficiency.

One thing to note here is that these flow measurements were taken at 28″ water pressure, or 1psi. As we know from supercharger theory, the higher the boost pressure (and the higher the pressure ratio), the more compressed the air. At 15psi, the air is 0psi ( or 1psi) the amount of boost is actually half. So to make 700hp (1050 CFM) @ 15psi (for example on a 3.5 liter 6 cylinder) a cross sectional area of ​​only 42 square inches may be needed (because air. half its original size) while 700hp ( 1050 CFM) @ 3psi (for example on a 7.0 liter 8 cylinder) may require a larger cross sectional area of ​​91 square inches. So consider your pressure ratio before choosing your cross sectional area.

Here is my second trend:

Horsepower (HP) = 0.533 * Intercooler Volume (cubic inches) + 50.17 

For the 30 cores I have data for this is Horsepower (vertical) vs. is a plot of total core volume (cubic inches). As you can see there is a linear relationship between horsepower and volume which is to be expected. The more horsepower we want to make, the more air we need to ingest. The higher the air mass; The more energy the mass can carry (at the same temperature compared to the smaller the mass) and thus you need to sink that energy into your intercooler.

I think it’s now possible to go back to my ‘twin-charged’ Toyota Celica in these two charts and say:

I wanted to make a peak of 320hp @ 20 psi. That is 480 CFM @ 2.36 pressure ratio.

Starting with the standard 3″ deep intercooler core, let me explain my other 2 dimensions:

Minimum cross area = ((480/2.36) + 12.84) /11.63 = 18 square inches = D*H

Height of intercooler = 18/3 = 6″

Total volume = (320 – 50.17)/0.533 = 506 cubic inches.

Intercooler Width = 506/18 = 28″

So my ideal core size is 28″ X 6″ X 3″ which is a very reasonable size front mount intercooler.

Now 28″ is a reasonable intercooler width for a pressure drop. If this figure were too big I would go back and use a 3.5″ deep core for example. Likewise, if my intercooler height doesn’t fit 6″ behind my bumper, I can go back and increase the depth a bit and redo the calculation.

The pressure drop across the intercooler is really important in tracking a supercharged car because unlike a turbocharger, we can’t just increase boost pressure with a boost controller, we’re limited with a supercharger to the gearing available in our supercharger pulley. So wasting any of that boost is really bad for performance. That’s why it’s really important not to downsize the intercooler to shut down the engine, or to oversize it to reduce high pressure.

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