Tomas L

What exactly are you saying?
If you mean that an air-water system cannot cool the intake air to ambient then your'e rigth. But that also implies to an air-air exchanger. No heat exchanger can lower the temperature of the cooled media down to the temperature of the cooling media.
If you mean that it cannot transfer all the heat that is removed from the intake air through the water system and then dissapate it to the ambient air in the watercooler, then you are very wrong.

Yes, the efficiencys of the air-water and the water-air units should be added together but that doesn't mean that the sum is greater than for an air-air unit. The efficiency of a heat exchanger largely depends on it's size, and since we can't and don't even want to put in an infinite sized heat exchanger we have calculate what's most efficient for our specific needs. The point here is that it depends on application which one that's more efficient. Many factors influence the result, space for the different units, acceptable intake system volume, pressure drop, driving conditions and much more. To generally state that one type is more efficient than the other is just ignorant.

Tomas

thesmokingman

Ignorant? Pardon me, but I don't think that's what he was eluding to. Space limitations are very big concerns to manufacturers when they consider the AWIC. Take the new Mini. When packaging limitations as well as crash requirements, prohibit the use of convetionally mounted FMIC using a AWIC is the only choice. Thus in all real world production situations, it comes down to a space consideration.

Tomas L

Then why was he saying this:
My point concerning ignorance was really not directed against John.. It was a more general statement because everytime there is a discussion of air-air vs air-water ic:s then someone states with strong words that the efficiency is lower due to the two heat exchangers.

Tomas

inactiveuser92616

there was a very well written hash out of air-air and water based intercooler setups on the Autospeed website. Since it is a payed subscription, I will try to summarize as accurately as I can:
Air-Air
Pros: Cheap, reliable, lightweight
Cons: Large, potentially very long and complicated air path, both to, from, and within the IC; causing more lag and pressure drop. Also hard to package in some situations.

Air-water-Air
Pros: Fits well in tight engine bays. Does not require complex air paths, and doesnt require near the amount of air volume within the IC; resulting in less lag and pressure drop.
Cons: Expensive, complex, heavier

My personal opinion, if you can keep the air path reasonable go air-air. Otherwise a well designed air-water-air will gain far more appreciable gains on the street, especially due to the decreased lag.

Dark Lightning

I can't think of another turbocharged car with shorter intercooler piping with a front mounted air-air intercooler than a 951.

thesmokingman

True, but I wish the same could be said of the hotside.

inactiveuser92616

oh forgot one of the pros that they listed for water based IC units; which is that during a heat spike they keep the temperature much lower, due to the high specific heat of water. In this mode it is more of a heat sink than a heat exchanger.

thesmokingman

I can't help thinking of my peltier based water cooled pc rig man...

DDP

comon guys, we all know that ait to water is the best! you know because the new supercharged saturn Ion has an air to water cooler....hahaha. I love saturn!

Matt H

What the hell is a heat spike? The temp over the surface of an air to air IC in theory, should be roughly that of the air passing through it.

If tomorrow, they said that adding a air to water IC added 5 HP it would still be one more place for the car to leak coolant (water), and there would still be all the associated plumbing, the issue of where to put it, etc.
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inactiveuser92616

Matt, say you are cruising along at low boost (and hence not that much heat passing through the IC). Now say that all of a sudden you romp on it, getting heavy into the boost, the intake air temp after the compressor sky rockets. Because water has a high specific heat (takes alot of energy to raise it one degree in temp) the water could absorb far more heat than the steady state heat dissipation capacity of the intercooler, for a short time. This would result in less of that suddenly high intake air temp actually getting to the engine, during that short period of ultra high compressor temps. Once back down at a lower boost, the water can slowly dissipate this heat through its own heat exchanger.

Think of the effect as being analagous to a capacitor in an electrical circuit, but instead of resisting voltage change the heat sink effect resists temperature change.

Duke

Since the air between the turbo and intake constantly is flowing through the IC there can be no such thing as a heat spike. The IC has no response time.

Tomas L

Spike may be the wrong word for it but if your driving pattern consists of short (perhaps up to 15 s) burst of boost followed by a period with no boost then an air-water system can take advantage of this. You can design the water cooler for the average load which will make it smaller than if it was design for continous full power load. The water will act as a buffer and even out the temperature over time.
If you design an air-air ic and an water-air ic so that both has the same thermal efficiency, say that both will drop temperature by 90% during continous full load situations, then the air-water will give much higher efficieny during the first seconds of full boost until the water has reached it's stady state operating temperature.

Tomas

Matt H

Duke, you hit what I was getting at.

Tomas, I see your point.
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951Tom

I have the Toyota parts catalog CD and it shows the set up a 94 turbo celica uses. You might be able to use parts from it. It has the little radiator, electric pump, and a fluid resevoir. The celica came with a 2.0L motor so I'm not sure if it's intercooler flows enough CFM for 951. In the parts diagram, the celica's electric pump looks alot like the 951 aux. pump to cool the turbocharger after shut-down.