WC Engineering > Technical Articles > Chargecooler Pumps
Chargecooler Pumps: Electric vs. Stock

There has been much debate about using the stock mechanical chargecooler pump or going to an electric pump. Here are my opinions on the matter. (And these are just my opinions, but this is what I work from and I think they make sense if you look at the issue logically.)

The stock pump's impeller is made by Jabsco and it is not intended to be spun over 3500 RPM or used in high temperature liquids. It deteriorates rapidly when used with coolant. Since the pump spins at half of engine speed, it also has a variable flow rate.

The Chargecooler System

So, let's look at the chargecooler system. We start with a turbo that generates a variable volume of air at a variable heat dependent upon engine load. This air is cooled by the chargecooler, which has a fixed heat transfer surface area. The chargecooler is cooled by liquid, fed by a pump, that also runs at a variable speed, which is dependent upon engine RPM. The liquid is pumped through a very large radiator that has a fixed thermal transfer surface area. The radiator is cooled by the air that passes over it. The amount of air is a variable dependent on the vehicles speed.

  • Air Volume
  • Air Temperature (Turbo Outlet)
  • Vehicle Speed
  • Pump Speed
  • Chargecooler Thermal Transfer Area
  • Radiator Thermal Transfer Area

    It is "intuitively obvious to the most casual observer" that the simplest way to improve this system would be to try to reduce or eliminate the variables.

    Can we limit/control the air volume through the chargecooler?
    Well... yes, but that would mean running less boost and it won't be fun to drive.

    Can we limit/control the intake charge air temperature?
    Yes, but it would require installing a more efficient turbo.

    Can we limit/control vehicle speed in order to get consistant air flow over the chargecooler radiator?
    Not a chance... who are we kidding...??

    Can we limit/control pump speed?
    Sure, get rid of the engine driver mechanical pump and replace it with a constant speed pump.

    Bingo! One less variable, which means the system can be better controlled and then studied for further improvement.

    Next, is more volume of flow better? I would say yes, to a point. I'm sure that there is a point where no matter how much faster you pump the system there is no improvement. There may even be a negative return point, but I have yet to find either point.

    If you choose to use one of my pumps or someone else's, please pay attention to flow rate at pressure. The Lotus chargecooler system needs a significant amount of head pressure to keep the coolant flowing and a minimum of 4 gpm and 16 ft of head pressure to keep the system efficient. So far in my testing, higher flow is better, but getting a higher volume pump that can sustain the pressure tends to draw a lot of current.

    Electric Chargecooler Pump Installation

    Choose a pump that has a volume flow of at least 4 gpm and 16 ft of head pressure. Most pumps that fall into this category are going to be non-self-priming, so the installation location should not require the pump to lift the fluid. Installation location should also take into account the hoses and electrical connections.

    In our experience, the preferred location for the pump has been under the trunk floor, above the transaxle, attached to the chassis cross brace. If the pump is mounted here, the stock hoses from the factory pump can be used in the new installation. The hose that comes from the front of the car up to the stock pump can be disconnected from the stock pump and routed back to the new pump on the cross member. The second hose can be removed from the stock pump and rotated 180 degrees to get it line up with the new pump. Depending on which pump you choose, a hose extension or adaptors may be needed.

    The power for the new pump can be obtained from either the rear relay box or the right hand relay box. Look at the current draw of your pump. If it is less than two amps you can tap into the fuel pump power supply to run the pump. If it is greater than two amps it is recommended to install an additional fuse for the pump and tap a switched power source. (FYI: The WC Engineering pump draws 1.8 amps at full load.)

    In any case, the stock mechanical pump should not be left in place. The seals, without fluid against them, will fail.

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