View Full Version : New Tech Article: Intercoolers and the importance of temperature and pressure drop

21-12-09, 11:04 PM

Hi All,

Now that we have been appointed as an official overseas distributor for ARC we have been doing quite a bit of research into efficient intercooler design.

In this article we will take an engineering approach to show the science behind efficient intercooler design, and why all intercoolers are not created equal.

This article will explore:

1. Temperature differences between intercooler inlet and outlet
2. Pressure differences between the intercooler inlet and outlet
3. How using a high quality intercooler can actually allow your turbo to produce the same level of boost at the throttle body, while your turbo is working LESS hard (which then potentially allows you to produce more boost with your stock turbo without inlet temperatures getting crazy).


The two key factors in how much power an intercooler will produce on your car are:

1. Minimising the restriction of the intercooler (minimising the pressure drop)
2. Getting the temperature of the intake air as cool as possible at the outlet of the intercooler.



On the Supercharged 911 the air temps right after the supercharger were very high, and fitting a high quality intercooler got the temperature of the intake charge relatively close to ambient temperatures - we will update this article with the exact data.

As you can see in the photo above, the intercooler on the Supercharged 911 is not a massive intercooler, but it's efficiency allows a smallish intercooler to cool the intake charge very efficiently.

Also note the smooth tapered design of the end tanks that allows the intake charge air to enter and exit the intercooler efficiently.


There is an excellent article here about intercoolers:


That article reads ...

At wide open throttle and full boost the hot compressed air coming from a turbocharger is probably between 250 and 350 deg F depending on the particular turbo, boost pressure, outside air temperature, etc.. We want to cool it down, which reduces its volume so we can pack more air molecules into the cylinders and reduce the engine's likelihood of detonation ...

Cooler air is denser than warmer air. By cooling the intake charge the oxygen molecules are packed more tightly. Cooler, denser air = bigger bang = more power.

This is why all turbocharged or supercharged cars make more power on cooler days or on cooler evenings than they do on a hot summer day.


The gnttype.org article continues:

The less hard the turbo has to work to compress the air then the lower the temperature the air coming out of the turbo is ...

You can work the turbo less hard by running less boost, by improving the pressure drop between the air filter and the turbo, or by having a more efficient compressor wheel. You can also reduce the pressure drop in the intercooler, which allows you to run the same amount of boost in the intake manifold while having a lower turbo discharge pressure ...

If you can drop the turbo outlet pressure by 2 psi, or raise the turbo inlet pressure by 1 psi, that will drop the turbo discharge temperature about 16 degrees (depending on the compression efficiency and boost level).

If the turbo air is going into the intercooler 16 degrees colder then it may come out only 10 degrees colder than before, but that is still better than what it was ...


Temperature drop is only one part of the equation. Because temperatures and pressures go hand in hand, the pressure drop of the intercooler also needs to be considered.

The pressure drop of an intercooler is a measure of how much restriction it has - how difficult it is for air to flow through it. Just like exhaust systems, the goal is to remove restriction and to have as little restriction as possible. So what you are looking for is an intercooler with a small pressure drop.

Pressure drop of an intercooler is calculated by this equation:

Pressure of the intake air at the inlet of the intercooler MINUS pressure of the intake air at the outlet of the intercooler.

So as an example, if the pressure of the intake air at the inlet of the intercooler is 19 PSI, and the pressure of the intake air at the outlet of the intercooler is 15 PSI, then the restriction of the intercooler has taken away 4 PSI of your boost ...

19 PSI minus 15 PSI = 4 PSI pressure drop.

So that intercooler would have a pressure drop of 4 PSI.

The smaller a pressure drop and smaller the restriction an intercooler has, the more of the power produced by your turbocharger or supercharger will make it to your intake manifold.

Conversely, the larger a pressure drop and larger the restriction an intercooler has, less of the power produced by your turbocharger or supercharger will make it to your intake manifold.

The gnttype.org article continues:

Another aspect of intercoolers to be considered is pressure drop.

The pressure read by a boost gauge is the pressure in the intake manifold. It is not the same as the pressure that the turbocharger itself puts out.

To get a fluid, such as air, to flow there must be a difference in pressure from one end to the other. Consider a straw that is sitting on the table. It doesn't having anything moving through it until you pick it up, stick it in your mouth, and change the pressure at one end (either by blowing or sucking). In the same way the turbo outlet pressure is higher than the intake manifold pressure, and will always be higher than the intake pressure, because there must be a pressure difference for the air to move.

The difference in pressure required for a given amount of air to move from turbo to intake manifold is an indication of the hydraulic restriction of the intercooler, the up pipe, and the throttle body.

Let's say you are trying to move 255 gram/sec of air through a stock intercooler, up pipe, and throttle body and there is a 4 psi difference that is pushing it along (I'm just making up numbers here). If your boost gauge reads 15 psi, that means the turbo is actually putting up 19 psi.

The article then mentions fitting some modified parts that increase the airflow of the engine and continues ...

Now you are moving 450 gm/sec of air. At 15 psi boost in the intake manifold the turbo now has to put up 23 psi, because the pressure drop required to get the higher air flow is now 8 psi instead of the 4 that we had before. More flow with the same equipment means higher pressure drop.

That "More flow with the same equipment means higher pressure drop" is not widely known by many modifiers.

The reason for that is because restriction is essentially a function of airflow, not a fixed amount of restriction in psi.

As you increase the amount of air that you are forcing through an intercooler, the measurement in psi of the pressure drop increases.

So in the example above:

- pushing 255 gram/sec of air through the intercooler produces 4 psi of pressure drop
- pushing 450 gram/sec of air through the intercooler produces 8 psi of pressure drop


The gnttype.org article continues:

So we put on a new front mount intercooler. It has a lower pressure drop, pressure drop is now 4 psi, so the turbo is putting up 19 psi again.

Now we add the 65 mm throttle body and the pressure drop is now 3 psi.

Then we add the 2.5" up pipe, and it drops to 2.5 psi.

Now to make 15 psi boost the turbo only has to put up 17.5 psi.

The difference in turbo outlet temperature between 23 psi and 17.5 psi is about 40 deg (assuming a constant efficiency)!

So you can see how just by reducing the pressure drop we can lower the temperatures while still running the same amount of boost.

Because the intake charge is cooler and denser, you reduce the risk of pinging and detonation.

And of course your car can then be retuned to take advantage of the cooler, denser intake charge, thereby maximising the benefits of the cooler intake charge.

For those modifying their cars for more power but trying to avoid the cost of an aftermarket turbocharger, an efficient intercooler also has a cost benefit ...

Because a highly efficient intercooler that reduces the pressure drop allows your engine to make more boost pressure at the throttle body without your turbo or supercharger having to work harder than it was working with a less efficient intercooler, a highly efficient intercooler can allow your car to produce more boost at the throttle body with your stock supercharger or stock turbocharger.

And of course for those with large aftermarket turbos, an efficient intercooler maximises the effectiveness of your turbo.


As with any scientific approach, gathering real data is the key.

To compare the efficiency of any two intercoolers so that any meaningful engineering efficiency comparison can be made, you need to measure at the very least:

1. The temperature of the intake charge at the intercooler inlet,
2. The temperature of the intake charge at the intercooler outlet,
3. The pressure of the intake charge at the intercooler inlet, and
4. The pressure of the intake charge at the intercooler outlet.

In addition, useful points to measure data at are:

5. The temperature of the intake charge at the outlet of the turbo / supercharger
6. The pressure of the intake charge at the outlet of the turbo / supercharger
7. The pressure of the intake charge at the inlet manifold
8. The temperature of the intake charge at the inlet manifold
9. Ambient air temperature
10. Vehicle speed (which helps calculate the speed of the air flowing through a front mount intercooler)

One of the ways to gather that data is to get some threaded sensor fittings mounted onto the intercooler piping before and after your existing intercooler, then use threaded temperature sensors and pressure sensors to get some data on your current air temps and current pressure drop.

As the temperature changes are affected by the amount of ambient air flowing through the intercooler, the test data needs to be gathered with the car moving, not sitting still - unless you happen to have a wind tunnel at home :)

So the simplest way to gather data from a moving vehicle is to fit threaded pressure and temperature sensors to the car, with their signals logged for later analysis.

Once you have that data, you can calculate:

- the pressure drop of your intercooler
- the pressure drop of your intake tract (from turbo outlet to inlet manifold)
- the temperature drop of your intercooler
- the temperature at your throttle body vs ambient.

Then when you replace your intercooler with a more efficient factory location intercooler or a front mount intercooler you can see immediately the effect that it has on intake temps and pressure drop.

A number of companies make intercooler temperature gauges, that are dash mountable, and a number of companies make standalone dataloggers. In addition, a number of aftermarket ECU's allow you to log data from additional temperature and pressure sensors, and there are also USB temperature and pressure sensors available if you want to log data to a laptop. We will update this thread with info about data logging options.

A high quality efficient intercooler core can make a big difference to inlet temperatures and pressure differentials, and similarly the end tank design is also an area in which high quality intercoolers can make a difference.


A number of high quality automotive brands have recently been the target of poor quality knock offs and counterfeits, often manufactured in south east Asia and in China.

While a knock off intercooler may look similar to the real deal Japanese made intercooler on the outside, the internal design of the intercooler core is an extremely important factor in achieving high efficiency intercooling.

The gnttype.org article continues:

I have seen some misunderstandings regarding intercooler pressure drop and how it relates to heat transfer. For example, one vendor's catalog implies that if you had little or no pressure drop then you would have no heat transfer. This is incorrect. Pressure drop and heat transfer are relatively independent, you can have good heat transfer in an intercooler that has a small pressure drop if it is designed correctly. ...

Pressure drop is important because the higher the turbo discharge pressure is the higher the temperature of the turbo air. When we drop the turbo discharge pressure we also drop the temperature of the air coming out of the turbo. When we do that we also drop the intercooler outlet temperature ...

This lower pressure drop is part of the benefit offered by new, bigger front mount intercoolers ... by bigger up pipes; and by bigger throttle bodies. You can also make the turbo work less hard by improving the inlet side to it ... these all reduce the pressure drop in the turbo inlet system which makes the compressor work less to produce the same boost which will reduce the turbo discharge temperature (among other, and probably greater, benefits).



ARC International Inc is based in Shizuoka, Japan. ARC has a reputation for top quality, precision made parts, made from the highest quality materials, and made by highly skilled engineers and fabricators in Japan.

More than 90% of all Japanese Super GTC / JGTC cars runs ARC oil coolers, including Honda, Nissan and Toyota.

Nakajima Racing team,which won the title of Formula Nippon this year, always uses ARC radiators and oil coolers. Satoru Nakajima is the first japanese full time F1 driver. He chose ARC products to win Formula Nippon.

Nissan and Toyota always ask ARC to develop their prototype intercoolers, radiators, and oilcoolers for big races. Especially ARC has had an excellent and successful relationship with Nissan Racing Department for a long time.

In designing their intercoolers, ARC regard balancing both reduction of pressure loss and high cooling efficiency as important to bring an increase of torque and smooth response.


The core inlet design on genuine ARC intercoolers is tapered, and every model is designed in one layer.

The load on the turbine is reduced by minimizing the loss of pressure.

Just as having smooth transitions in an exhaust system affects airflow efficiency, the tapered core inlets on genuine ARC intercoolers improve airflow through the inside of the intercooler core. This is one way in which ARC addresses pressure loss.


Genuine ARC Front Mount Intercoolers use a Straight Fin design. This allows for smooth air flow and reduces the load on the radiator.


By buying an appropriately sized quality front mount intercooler manufactured by an original Japanese aftermarket manufacturer like ARC, you then can also keep that intercooler as you upgrade your car in the future, so it is ready to handle a larger turbo later etc without needing to replace the intercooler again later.

ARC also has an excellent tech page about their intercooler technology here ...




There's a saying in the engineering business ...

"Any product can be be made more cheaply by making it worse".

Like almost all automotive products, this will ALWAYS apply to intercoolers.

All our ARC products are guaranteed 100% genuine ARC products and are sourced only directly from the ARC factory in Japan to guarantee authenticity.

The Tuners Group is one of only 8 ARC factory authorised overseas distributors worldwide outside of Japan listed on the ARC website. We are supplied directly by the ARC factory in Japan.

By purchasing from us you are absolutely assured of getting the genuine, real deal, ARC product.

The full range of genuine ARC front mount intercoolers have been listed on our website. ARC's range of replacement intercoolers will be added to our website shortly - please contact us if you need an intercooler that is not listed.

You can browse our range of genuine ARC Intercoolers here:


More information on the full range of ARC products can be found here ...