air/air vs water/air intercooler?

In reply to Boost_Crazy:

I never said "ultimate cooling capacity" I said water cools better than air so it's rather "ultimate cooling efficiency"

chiodos wrote: Air to air and water to air are not equal. Keep reading. If what you say is true (still cooled by air regardless) why are there ZERO air cooled cars anymore? Oh that's right, because water cools better than air. It's science.

air cools everything, unless like said above, you are using raw water cooling on a boat. Even an engine with a radiator and water cooling, uses air cooling to keep the radiator cool.

The only reasons there are no air cooled cars, is Noise, vibration, and harshness combined with a need to keep emissions equipment happy. Packaging is also a bit plus. If you ever looked at a Porsche Flat six, you actually are not looking at the engine, just the intake and all the cooling parts.

Yes, the air still has to do the cooling in the end. But an air/water system will take more heat into the system before it heat soaks enough to see the same increase in charge air temp as an air/air system, so it'll be more effective on a quick throttle blast at low vehicle speeds (such as autocross). Plus, you can ice the tank if it's a separate water loop. Under sustained high power (like a truck towing something up a mountain), they'll be a lot more equal, as either one will heat-soak to equilibrium.

Air/water heat exchangers are also a little more efficient than air/air, so you can often fit a little more cooling capacity within your space constraints up front (and you can use multiple smaller radiators to get more total surface area if that's more practical on your car, while things like that get bulky and have pressure drop concerns with air/air).

Yes air cools everything, but using water as a transfer medium is more efficient because water transfers energy at a much higher level than air. Besides an intercooler is a massive heat sink, it can only shed heat after it has absorbed it, but! If your running say a 20 sec pull in boost, that intercooler will get to let's just say 250f in a hurry, the intake air is 250 so it can't get any higher but it also cannot get any colder because the heat sink is still trying to shed that heat (must shed heat before it can absorb more) now in an air to water intercooler, it has to heat ALL THE LIQUID before it gets to that same point that the air to air intercooler got to in mere seconds. All it takes is 30 seconds worth of math to be sure you can shed the heat out of the exchanger fast enough, have enough liquid capacity, and enough flow. Where your air to air intercooler is heat soaked before the first turn, the air to water intercooler is still chugging keeping cool after laps and laps. As long as it was designed properly that is.

In reply to rslifkin:

Finally someone else knows...

In reply to rslifkin:

The heat soak effect of water is only as good as how cold it starts with. If you are on the starting grid, and have warmed up the engine enough so that it's properly warm (as in oil isn't causing drag, which it does), there's a good chance that the water in the cooler system was warmed up quite a bit- since most of them are sitting in close proximity to the engine.

For an autocross, I don't see a big advantage one way or another- most air coolers are sized really well, too.

IF you can run ice (which I'm not aware of any bodies that allow ice cooling other than GRM for the challenge), that is a big deal.

That being said, the likely amount of heat soak isn't going to be a big deal either way. If one can get the intake air down to 100F, you will be in good enough shape.

BTW, one big reason water coolers are in favor even though one failure mode will kill the engine is that they DO retain heat. Having it always at 100F keeps liquid water out of the intake stream, which is a good thing, as it's commonly the cause of slow burns and misfires.

Both systems will work fine. The air-air system is simpler but harder to package. The water-air system has more parts than can be a pain, but is pretty easy to package. And the weight disadvantage can be lost in what you had for breakfast.

chiodos wrote: Yes air cools everything, but using water as a transfer medium is more efficient because water transfers energy at a much higher level than air. Besides an intercooler is a massive heat sink, it can only shed heat after it has absorbed it, but! If your running say a 20 sec pull in boost, that intercooler will get to let's just say 250f in a hurry, the intake air is 250 so it can't get any higher but it also cannot get any colder because the heat sink is still trying to shed that heat (must shed heat before it can absorb more) now in an air to water intercooler, it has to heat ALL THE LIQUID before it gets to that same point that the air to air intercooler got to in mere seconds. All it takes is 30 seconds worth of math to be sure you can shed the heat out of the exchanger fast enough, have enough liquid capacity, and enough flow. Where your air to air intercooler is heat soaked before the first turn, the air to water intercooler is still chugging keeping cool after laps and laps. As long as it was designed properly that is.

Doing the math to solve that problem is 6 of one and half dozen of another- that's an easy problem to solve regardless of what kind of cooling you choose. Heat exchangers are a Jr level engineering class. Very well known.

alfadriver wrote: In reply to rslifkin: The heat soak effect of water is only as good as how cold it starts with. If you are on the starting grid, and have warmed up the engine enough so that it's properly warm (as in oil isn't causing drag, which it does), there's a good chance that the water in the cooler system was warmed up quite a bit- since most of them are sitting in close proximity to the engine.

Easy fix: run an electric fan (either for everything or just on the cooler for the air/water system) and force the fan to stay on while you're waiting to start your run. That should have you starting your run with the water not much above ambient temp.

rslifkin wrote:

alfadriver wrote: In reply to rslifkin: The heat soak effect of water is only as good as how cold it starts with. If you are on the starting grid, and have warmed up the engine enough so that it's properly warm (as in oil isn't causing drag, which it does), there's a good chance that the water in the cooler system was warmed up quite a bit- since most of them are sitting in close proximity to the engine.

Easy fix: run an electric fan (either for everything or just on the cooler for the air/water system) and force the fan to stay on while you're waiting to start your run. That should have you starting your run with the water not much above ambient temp.

Which works for both systems... Not sure how that make water better than air.

Well, actually, that can be seen to hurt water systems- since so much of it's medium is underhood- with the fans on, and a hot radiator, you mix the underhood warm air up, so all the water underhood will be nice and warm. The fan only cools the water in the front, not underhood. Theoretically.

With the air system, a the entire cooling system is in front of the radiator, so the fan will make sure that the air cooler is at ambient....

One system isn't as clearly so much better as you try to point out, that's more my point. Everything has it's compromises- it's a matter of understanding them.

alfadriver wrote: Which works for both systems... Not sure how that make water better than air. Well, actually, that can be seen to hurt water systems- since so much of it's medium is underhood- with the fans on, and a hot radiator, you mix the underhood warm air up, so all the water underhood will be nice and warm. The fan only cools the water in the front, not underhood. Theoretically. With the air system, a the entire cooling system is in front of the radiator, so the fan will make sure that the air cooler is at ambient.... One system isn't as clearly so much better as you try to point out, that's more my point. Everything has it's compromises- it's a matter of understanding them.

The water is circulating, so it'll get the whole system close to ambient (a little warmer, due to heat absorbed from the engine bay). But the difference is, once you get on the throttle, that air/air intercooler will heat up to, say, 200* within seconds. The water will take longer to heat up to that point, so you'll have better cooling for the first part of your run (on a long course, they'll likely equal out by the end, as both will be heat-soaked).

Now if you start using mechanical cooling (ie Direct Expansion) or change the heat exchanger's mode of operation from a 'dry cooler' to an 'evaporative cooler' (IE spray water on it), you can increase the overall efficiency of either of the two systems.

So just by spraying water on the surface of the heat exchanger, you could potentially reach the wet bulb temp. So in Atlanta on a 93°F DB day, you could be a cooling effect of 74°F WB. That's an extra ~20°F difference. You could use a system like that to precool the heat exchanger or for WOT portions.

I think the one thing missing in this conversation is routing. An air to water IC setup allows for a minimum of IC piping. Rather than having to shove pressurized air down to the bumper, then back up to the intake and into the engine, you can mount a small "box" of an Air/water intercooler inline with the intake.. or even as part of the intake as the supercharged Saturn Redlines did.

Another plus, you can run multiple small radiators.. so like in the skyline, you can run a small one behind each foglight, or a long slender one infront of the main radiator. If you really needed to, a small fan can be used to help "force cool" the radiators

rslifkin wrote:

alfadriver wrote: Which works for both systems... Not sure how that make water better than air. Well, actually, that can be seen to hurt water systems- since so much of it's medium is underhood- with the fans on, and a hot radiator, you mix the underhood warm air up, so all the water underhood will be nice and warm. The fan only cools the water in the front, not underhood. Theoretically. With the air system, a the entire cooling system is in front of the radiator, so the fan will make sure that the air cooler is at ambient.... One system isn't as clearly so much better as you try to point out, that's more my point. Everything has it's compromises- it's a matter of understanding them.

The water is circulating, so it'll get the whole system close to ambient (a little warmer, due to heat absorbed from the engine bay). But the difference is, once you get on the throttle, that air/air intercooler will heat up to, say, 200* within seconds. The water will take longer to heat up to that point, so you'll have better cooling for the first part of your run (on a long course, they'll likely equal out by the end, as both will be heat-soaked).

Both systems will have air inlet at the higher temp due to boosting.

But I think you are picturing an air-air cooler in a system where the ambient air around the cooler is not moving. It is, as that's how a heat exchanger works. The air around the cooler will be ambient all the time- and since air is flowing through the cooler, it's always being replaced by ambient air. So much so that by the time the high pressure/high temp air passes through, it will be cooled.

Both systems are designed to cool from say 200F to 100F at peak flow. That's how they work.

mad_machine wrote: I think the one thing missing in this conversation is routing. An air to water IC setup allows for a minimum of IC piping. Rather than having to shove pressurized air down to the bumper, then back up to the intake and into the engine, you can mount a small "box" of an Air/water intercooler inline with the intake.. or even as part of the intake as the supercharged Saturn Redlines did. Another plus, you can run multiple small radiators.. so like in the skyline, you can run a small one behind each foglight, or a long slender one infront of the main radiator. If you really needed to, a small fan can be used to help "force cool" the radiators

And that system requires multiple pumps and more fans. And while those require some kind of nominal load, it's also non-zero. Fans especially. Everything has a compromise.

RossD wrote: Now if you start using mechanical cooling (ie Direct Expansion) or change the heat exchanger's mode of operation from a 'dry cooler' to an 'evaporative cooler' (IE spray water on it), you can increase the overall efficiency of either of the two systems. So just by spraying water on the surface of the heat exchanger, you could potentially reach the wet bulb temp. So in Atlanta on a 93°F DB day, you could be a cooling effect of 74°F WB. That's an extra ~20°F difference. You could use a system like that to precool the heat exchanger or for WOT portions.

FWIW, getting to the wet bulb temp can be risky. Unless the water that is condensed out of the air is evenly distributed across all of the cylinders, it's possible to have a stream of water going into one- which can be bad for combustion. Seems good, but too much can really hurt things. Seen it a lot.

Jumper K. Balls wrote: I just can't see how jamming all that stuff into an engine bay is easier or packages better than a front mount air/air

What is that kit for from Madness?

All I can say is if you don't want boost lag, don't use 2 side mount a2a's sandwiched in weird places like Fiat did....

Edit: NVM, it's for "das Mini"

In reply to WOW Really Paul?:

I have no idea. Googled air to water intercooler kit and that image came up.

Everyone tells me to go air/water in the Fiat which is incredibly tight in the bay already and is all about being a featherweight so the added mass and complication turns me off.

In reply to chiodos:

Yes air cools everything, but using water as a transfer medium is more efficient because water transfers energy at a much higher level than air. Besides an intercooler is a massive heat sink, it can only shed heat after it has absorbed it, but! If your running say a 20 sec pull in boost, that intercooler will get to let's just say 250f in a hurry, the intake air is 250 so it can't get any higher but it also cannot get any colder because the heat sink is still trying to shed that heat (must shed heat before it can absorb more) now in an air to water intercooler, it has to heat ALL THE LIQUID before it gets to that same point that the air to air intercooler got to in mere seconds. All it takes is 30 seconds worth of math to be sure you can shed the heat out of the exchanger fast enough, have enough liquid capacity, and enough flow. Where your air to air intercooler is heat soaked before the first turn, the air to water intercooler is still chugging keeping cool after laps and laps. As long as it was designed properly that is.

You are skipping, missing, or completely ignoring the important parts of this discussion. Yes, water absorbs heat better than air. It also retains heat better than air. That is why is is a good transfer medium for cooling (radiator) or heating (heater core). But the water is NOT doing the cooling. It is moving the heat from one area to another. With an Air/Water I/C, the purpose of the water is to move the heat from the air charge to the front mounted heat exchanger. Not to cool. You are so confident that you know what you are talking about, because "It's science," that you have failed to take a step back and look at what you are actually saying and comparing. Someone gave you a clue a while back- you are comparing appes with oranges. The water is just the transportation system. A transportation system that IS NOT PRESENT with an Air/Air system, because the air charge is introduced directly to the intercooler. There is ONE heat exchanger with Air/Air, not TWO as in Air/Watet, so there in no need for the connection. Your theory would only be correct if you were to empty the water out of an Air/Water system and try to pump air through it instead- that is the comparison that you think you are making, which is why you think you are right. But step back, and you will see it's absurd.

Air/Water does have benefits. As long as the water remains below ambient temp, it does do a better job. But once it is over, it retains heat longer, and does a worse job. Heat both systems up, and I guarantee the Air/Air recovers quicker. There are a lot of other factors- internal flow through the core, pressure drop, pipe sizing and bends, etc, but that is a whole different discussion.

Given optimal cooling air flow across the air/air core and the water radiator, there should be very little difference in performance. However, as that flow varies or drops off (such as in traffic or at low vehicle speeds), the air/water setup will see slower temperature variations and will take longer to heat soak when you get into boost.

So if you're sitting in traffic and then it clears up and you go WOT, the air/air setup may see a spike in intake temps (depending on whether the cooling fan was on or off, so whether or not the core was fully heat soaked), while the air/water setup will just see a slow rise in IAT until you get enough road speed to start cooling the system back down, and the result will be more consistent (the variations in system temp / heat soaking due to the cooling fan cycling in traffic are smoothed out by the water's ability to retain heat).

Based on that point, think of it this way: assuming a 75 degree day the air/air core may be varying between 80 and 120 as the fan cycles while idling in traffic, while the water temp is only varying between 97 and 103. When you go WOT, if the fan happens to be off at that moment, the air/air cooler is going to go from 120 to much hotter very quickly, and then start dropping and become effective as road speed / air flow increases. The air/water system will see a rise in water temp when you go WOT until the road speed / air flow starts to come up and cool things back down, but that rise will be much slower, as the system can absorb more heat before reaching, say 200 (with very little heat actually being shed), so the highest IAT you'll see at the spike will be lower (as it only has to absorb heat for a second or 2 until you're going fast enough to have good airflow again).

Basically, the performance advantage of an air/water setup isn't in steady state performance, it's in ability to maintain lower IAT during short WOT blasts, particularly under low airflow conditions. And sometimes, the increased consistency is a benefit as well.

mad_machine wrote:

chiodos wrote: Air to air and water to air are not equal. Keep reading. If what you say is true (still cooled by air regardless) why are there ZERO air cooled cars anymore? Oh that's right, because water cools better than air. It's science.

air cools everything, unless like said above, you are using raw water cooling on a boat. Even an engine with a radiator and water cooling, uses air cooling to keep the radiator cool. The only reasons there are no air cooled cars, is Noise, vibration, and harshness combined with a need to keep emissions equipment happy. Packaging is also a bit plus. If you ever looked at a Porsche Flat six, you actually are not looking at the engine, just the intake and all the cooling parts.

It is very hard to get air directed to the hot areas in a cylinder head. This is why Porsche never made a four valve air cooled cylinder head, the racing engines had watercooled heads and all street aircooled sixes were two valve.

When Porsche went to water cooling, there was an instant bump in horsepower because they could cool more adequately.

This is neither here nor there, we're not talking about cooling a complex device with different thermal issues, we're just trying to make hot air less hot. And for this, water/air is still awesome because your effective heat exchange area is the size of the water radiator. You can fit a LOT more water radiator in the nose of a car than you can fit an air-air intercooler.

The RX-7 turbo guys switching from air-air to air-water are seeing lower inlet temps. It's not rocket science, it's the ability to get more cooling surface into the nose.

Downsides - more complexity, there's now a pump that can fail.

The downsides must not be too bad because a lot of OEMs are going to air-water charge cooling.

In reply to rslifkin:

I don't get your logic.

Given your situation, the outlet of the compressor/inlet of the cooler for both air and water will spike with the increase pressure. No question about that.

The cooling media for the air-air system will be at ambient or maybe slightly higher standing still. Once the car starts to move, the cooling air will be at ambient very quickly. There's not enough heat in the system to warm up the entire environment.... So the air-air system will try to cool to ambient if the fan is on or the car is moving. And the size of the cooler is designed to cool the whole thing to ambient at a nominal air flow across the front of the car.

The cooling media for the air-water system will be whatever it is underhood, with some cooling it's own air-water cooler. It absorbs the heat, and then moves to a heat exchanger which is located just like the air-air system and dumps the heat into the ambient environment.

Again, you seem to be missing the idea that the air-air cooler is dumping it's heat into the ambient air directly, and that ambient air is not a closed box.

alfadriver wrote: Given your situation, the outlet of the compressor/inlet of the cooler for both air and water will spike with the increase pressure. No question about that. The cooling media for the air-air system will be at ambient or maybe slightly higher standing still. Once the car starts to move, the cooling air will be at ambient very quickly. There's not enough heat in the system to warm up the entire environment.... So the air-air system will try to cool to ambient if the fan is on or the car is moving. And the size of the cooler is designed to cool the whole thing to ambient at a nominal air flow across the front of the car. The cooling media for the air-water system will be whatever it is underhood, with some cooling it's own air-water cooler. It absorbs the heat, and then moves to a heat exchanger which is located just like the air-air system and dumps the heat into the ambient environment. Again, you seem to be missing the idea that the air-air cooler is dumping it's heat into the ambient air directly, and that ambient air is not a closed box.

I'm referring to what will happen in that first 1 - 2 seconds before you have enough forward speed to get significant airflow. Once your speed comes up enough, they'll be a lot more equal (and the air/air will actually drop to a lower temp faster, assuming both systems have the same heat dissipation capacity). The difference is that until you start to get noticeable forward speed (assuming fans aren't running), the air/air cooler has very little ability to take heat out of the charge air, while the air/water still has some until the water heats up to the temperature of the incoming charge air.

Knurled wrote:

mad_machine wrote:

chiodos wrote: Air to air and water to air are not equal. Keep reading. If what you say is true (still cooled by air regardless) why are there ZERO air cooled cars anymore? Oh that's right, because water cools better than air. It's science.

air cools everything, unless like said above, you are using raw water cooling on a boat. Even an engine with a radiator and water cooling, uses air cooling to keep the radiator cool. The only reasons there are no air cooled cars, is Noise, vibration, and harshness combined with a need to keep emissions equipment happy. Packaging is also a bit plus. If you ever looked at a Porsche Flat six, you actually are not looking at the engine, just the intake and all the cooling parts.

It is very hard to get air directed to the hot areas in a cylinder head. This is why Porsche never made a four valve air cooled cylinder head, the racing engines had watercooled heads and all street aircooled sixes were two valve. When Porsche went to water cooling, there was an instant bump in horsepower because they could cool more adequately. This is neither here nor there, we're not talking about cooling a complex device with different thermal issues, we're just trying to make hot air less hot. And for this, water/air is still awesome because your effective heat exchange area is the size of the water radiator. You can fit a LOT more water radiator in the nose of a car than you can fit an air-air intercooler. The RX-7 turbo guys switching from air-air to air-water are seeing lower inlet temps. It's not rocket science, it's the ability to get more cooling surface into the nose. Downsides - more complexity, there's now a pump that can fail. The downsides must not be too bad because a lot of OEMs are going to air-water charge cooling.

Interesting example to use.

Since the amount of cooling needed to cool the engine is far higher than to cool 200F intake air.

BTW, I'm not saying one is that much superior to others in all situations. The real answer is that what you need depends on your situation. For OEM's, probably the best thing about water-air coolers is that it keeps the intake warm when you need it, and cool when you need it.

rslifkin wrote:

alfadriver wrote: Given your situation, the outlet of the compressor/inlet of the cooler for both air and water will spike with the increase pressure. No question about that. The cooling media for the air-air system will be at ambient or maybe slightly higher standing still. Once the car starts to move, the cooling air will be at ambient very quickly. There's not enough heat in the system to warm up the entire environment.... So the air-air system will try to cool to ambient if the fan is on or the car is moving. And the size of the cooler is designed to cool the whole thing to ambient at a nominal air flow across the front of the car. The cooling media for the air-water system will be whatever it is underhood, with some cooling it's own air-water cooler. It absorbs the heat, and then moves to a heat exchanger which is located just like the air-air system and dumps the heat into the ambient environment. Again, you seem to be missing the idea that the air-air cooler is dumping it's heat into the ambient air directly, and that ambient air is not a closed box.

I'm referring to what will happen in that first 1 - 2 seconds before you have enough forward speed to get significant airflow. Once your speed comes up enough, they'll be a lot more equal (and the air/air will actually drop to a lower temp faster, assuming both systems have the same heat dissipation capacity). The difference is that until you start to get noticeable forward speed (assuming fans aren't running), the air/air cooler has very little ability to take heat out of the charge air, while the air/water still has some until the water heats up to the temperature of the incoming charge air.

Sure it does. Just like the water system does.

You claim that you can have the fan on- so that cools the heat exchanger to ambient. If you have it on to keep the water at ambient, then the air system can have it on to keep ambient air flowing across it.... Which is fast enough to cool the engine.

Why is it the fans are on for the water system to prevent heat soak but off on the air system???

1-2 seconds of a small increase of air temp isn't going to make much of a difference, anyway.

All it takes is 30 seconds worth of math to be sure you can shed the heat out of the exchanger fast enough, have enough liquid capacity, and enough flow. Where your air to air intercooler is heat soaked before the first turn, the air to water intercooler is still chugging keeping cool after laps and laps. As long as it was designed properly that is.

Sorry, you had so much incorrect with your overall theory that I forgot to address this. You are not describing an intercooler, you are describing a heat sink. The ability to shed heat is defined by the heat exchanger. It is designed to shed heat, not store it. That is why the surface area, fins, and airflow are important. If it was just a heat sink, you could put it in the trunk. The water diminishes this ability (it wants to store the heat). Think about how you actually drive a car. You are not WOT the whole time, even on a race track. Say you have two cars racing against each other, one Air/Water, the other Air/Air. The both start with the I/C's at ambient temp. The Air/Water has an initial advantage, as the water does act as a heat sink and less heat is transferred to the heat exchanger. Once the water is up to temp, the two would perform equally. Down the back strait, both cars WOT, the air charge after the I/C's are the same temp. Into the braking zone, off the throttle, the Air/Air cools quicker since it is less of a heat sink, and is more ready to accept the next hot air charge. For anything other than that to be true, the intercoolers would have to be so efficient that the air temp at the outlet would be the same no matter how hot or how long an air charge the inlet receives, and there would be no need for recovery. Do the 30 second math on that one, and tell me how large the core would need to be.