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The mkiv Supra Owners Club

Charge Coolers


Alex
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A friend of mine ask me why I wasn't considering a Charge Cooler instead of an FMIC. I couldn't answer him as I didn't know enough about charge coolers to really comment. He's not a Supra owner or a mechanic he's just heard of Charge Coolers and knows what there basic function is. So don't have a go at the guy for suggesting it - if its a really bad idea!

 

So if anyone can explain the differences etc then I'd love to know.

 

Regards

 

Alex H

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A charge cooler is basically an air to water intercooler instead of the usual air to air intercooler most of us are familiar with.

 

Water can absorb heat some 17 times faster than air. If you heat a piece of 10mm steel bar, say, to red heat and waft it around in the air then it will take several minutes to cool. However, dunk it in a pan of water and it will cool in seconds. Because of this much greater cooling efficiency, air to water intercoolers can be made much smaller than the equivalent air to air unit.

 

Their use is common in forced-induction marine engines where the massively increased efficiency of an air to water intercooler allows much greater intake densities. Which, in turn, leads to some incredible power gains.

 

Intercooler efficiency is normally expressed as a percentage. The best that can reasonably be expected of an air to air unit would be something like 70%. Which means that the intercooler has removed 70 percent of the heat that was put their due to the air having been compressed by the turbos. However, a marine air to water unit has the potential to provide efficiences beyond 100%. That is to say, the intercooler itself cools the air to below ambient temperature despite the air having been compressed.

 

The reason why this is possible is due to the unlimited supply of relatively cool seawater which is constantly pumped through the intercooler. The water takes away the heat of the charge (thus heating the water) and this heated water is simply discharged back into the sea, while a fresh load of cool water is being pumped in.  

 

Their uses are somwhat limited for automotive use due to a lack of a continuous source of cool water. The heat removed from the intake charge is absorbed into the water pretty rapidly, but then has basically no place to go. What normally happens is the water is piped to radiators at the front of the car.

 

So, in the first stage of the process, you get an efficient 17 times faster absorbtion of heat from the intake charge into the water. However, at the other end, you have the same heat transfer process but in reverse: a 17 times slower transfer of heat from the water into the air. So you don't really gain anything. In fact, the efficiency will be less than an equivalent air to air intercooler due to pumping losses, etc.

 

Where a charge-cooler can be of advantage is where a normally aspirated engine has been converted to forced induction. Often, there is simply no room for an efficient air to air intercooler at the front of the car. So the next best thing would be an air to water unit. While although having the disadvantage of a lower overall efficiency, it has the big advantage of being more flexible in the actual location of the component parts of the system. Plus, the overall setup will be far better than the only other option available which is to have no intercooling at all.    

 

Yours,

J

 

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How about a charge cooler with Liquid Nitrogen then!!! Stick a tank of it in the boot and cycle it through the charge cooler! Must be good for a couple of hours at least!

 

Only joking - I'm not completly insane you know!

....but the more I think about it.......

 

Cheers for the explanation, nice to find someone who does actually know everything!... :)

 

 

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Your idea is perhaps not as whacky as you might think. The technique is used on some drag cars. They have a tank in the car filled with ice cubes and the charge-cooler water flows through the cubes thus making it very cold. It doesn't last long, of course, but then again it doesn't have to. You only need enough to last one run then you re-fill with more cubes for the next one.

 

Yours,

J

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