Liquid Intercooling


Image showing the PWR barrel style liquid intercooler on the ca18det motor.

Of all of the mods I have done to the 240sx, liquid intercooling is the one that raises the most eyebrows, receives the most praise and insults and generally leaves people scratching their heads. This tech article is going to walk through the thought process and design considerations involved in liquid intercooling your Nissan 240sx. This is not a step by step walk but more along the lines of a reference article that will provide more than enough information to allow even novice mechanics to enjoy the benefits of liquid intercooling.

The Difference

The fundamental difference of the liquid intercooler is that it uses liquid (water) instead of air as a heat transfer medium. Water can absorb 14 times more heat than air and in a properly designed liquid intercooler system, there are several variables that can be tweaked to yield cooling efficiency beyond that of traditional air to air intercooling.

Designing for the Street

There are two major variants of liquid intercooling, those seen on drag only cars and those that run an additional heat exchanger for use on the street and track. I will be focusing on the latter. The components involved in a street system include:

  1. The liquid intercooler. I prefer the PWR barrel style coolers as they allow for the shortest possible intercooler piping.
  2. An electric water pump like the one from an F-150 Lightning. This is used to circulate the water through the system.
  3. A front heat exchanger such as an oil cooler or a Mustang Cobra unit. The heat exchanger functions as a radiator for the intercooling system and transfers heat back to the air.
  4. (Optional) A reservoir tank large enough to a) increase the amount of water in the system and b) fill up with ice to gain over 100% cooling efficiency for short bursts. Ice is typically used in the drag racing variant but can yield huge gains in horsepower over short periods.

Image showing the necessary components in a liquid intercooled system.
Pictured above is the Cobra heat exchanger, Lightning electric water pump and PWR barrel style intercooler. (Not to scale)

How it all Works

Unlike an air to air system where the compressed air is cooled directly by ambient air, the liquid to air system cools the compressed air with water and then the water is circulated to the front heat exchanger where the water is then cooled by the ambient air. In any system the water pump is mounted at the lowest point to ensure that it is always primed. The fill point should be the highest point in the system to allow for the bleeding of air bubbles. In the system I designed for the 240sx, the water pump is mounted next to the frame rail using a custom bracket and is hard wired to the battery with an on/off switch located in the cabin. The outlet of the pump is connected to the inlet on the liquid intercooler. The outlet of the liquid intercooler will then connect to the heat exchanger’s inlet. Also note that between the heat exchanger’s inlet and the liquid intercooler is where a water reservoir and/or fill point can be placed. After flowing through the heat exchanger, the water then exits back to the water pump to start it’s trip over, thus creating a closed system. Heater hose is use for all connections.

Whew, that was a mouthful. The image below should clarify things for you.

Diagram from the spearco website showing a general liquid intercooler design.

This diagram is from the Turbonetics website and shows the general layout of a liquid intercooled system.


Now that you know how a liquid intercooled system works I will go over the exact advantages of this system. Aside from the main sacrifice of simplicity, the liquid intercooler benefits from:

  1. Increased resistance to heat soak. For instance, in stop and go traffic, an air to air intercooler will heat soak meaning that it can no longer remove anymore heat from your intake charge. Heat soak also happens to liquid systems but since water has a 14 times greater capacity to absorb heat and cools the intake charge indirectly, the liquid intercooler does not heat soak as fast as the air to air counterpart. Also, the simple addition of an electric fan to the heat exchanger will provide sufficient air flow to cool the water even with the vehicle parked.
  2. Water in the heat exchanger flows slower through the system than the air in an air to air system. This allows the water to shed more quantities of heat at each pass than the quick single pass that happens in an air to air intercooler.
  3. Using a heat exchanger as an indirect cooling method allows the use of very efficient intercooler designs with the absolute minimum of piping. By avoiding the long maze of piping found in traditional intercoolers, liquid systems can literally run directly from the turbo to the intake manifold. By decreasing the overall piping length, boost and throttle response are increased.
  4. Ice can be added to systems running water reservoirs allowing aver 100% cooling efficiencies. Cooler air = more horsepower. However, even without ice the liquid system will run just as efficiently as an air to air system with the added benefit of taking longer to reach maximum temperature.
  5. Without the need for a huge front mount, one word pops into mind, sleeper.

And with that said we’re done. As always, I check the forums daily so if you have any questions or input I can be contacted there.


By 240am

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