Rogue Systems Charge Cooler

[white/mr2gtt]

i was on the rogue site n saw the charge cooler kit n was wondering if anyone has it n is it a worth while peice of kit. specially for the price! would an uprated intercooler b just as good cause they seem cheaper by bout 200 quid

[Jimlad]

Charge cooler should be better than any aftermarket intercooler for the mr2. Just depends on what you're wanting to do with your car.

[KiwiMR2]

The following is long and Im sure many of you won't read it all BUT it does pose some interesting questions AGAINST charge cooling, Im not sure which way I'd swing if I had the choice again......for up to 300 RWHP I think I'd stay air to air.

Also a lot of people realise the significant advantages of w/a in a mid mounted car

Care to quantify those "significant" advantages? Do they include extra cooling system drag, added weight, additional failure points, reduced efficiency, greater tendency to heat soak under prolonged boost?

While you're at it, would you care to explain why Ferrari & Porsche used Air to air I/Cs on their mid/rear engined cars, or for that matter why all the F1 turbo cars used Air->Air, with the exception of the early Renaults which used series charge cooling before dropping the Water->Air component after 2 races?

It's not that I don't think that W/A has it's place, it's just that no one has yet shown that you can't get the cooling required by using a properly sized Air->Air unit mounted in the stock location. Instead of bothering to do adequate research on the topic, people assume that by the looks of it you can't get adequate airflow through the side vents, which is obviously not the case as the intake also has to breath through there.

IMHO Water->Air has as many disadvantages as it has advantages, and, apart from drag racing and dyno queens, none of the advantages are significant. Seeing as I care about neither dyno figures, or living my life 1/4 mile at a time, I'll stick with the Air-> Air solution, though perhaps not in the stock location

Alright, I didn't mean that it was better in all circumstances, but it does have many advantages, for instance the ability to make use of the area at the front of the car that sees a lot of airflow,

Airflow, or pressure??? Just because the front has a high pressure, doesn't mean it has a high pressure differential and therefore high flow, also there is the issue of cooling system drag.

You might have to to explain what you mean by cooling system drag, are you talking airflow through the radiator?

Cooling system drag, as in drag created by the cooling system, not as insignificant as most people would assume, in most cars it makes up around 15% of the total drag, in a low cd car like the SW20 it would probably be higher.

Also the long periods of boosting that create heat soak in a water/air system are the sort of things you'd find on a race track, and I certainly don't remember saying anything about w/a being superior for race use.

Also these can be found on the streets, my favourite back road is about 10kms of twisting roads that see 80% or more throttle for a large percentage of the time. I used to have a image of the log which showed how long the stock I/C took to heat soak and how fast it recovered. Even with that severe abuse it didn't exceed 70°C, which considering how much !Removed! people pour on the stock I/C is a lot better than anyone would expect.

I said it had significant advantages, I should've added depending on circumstances. In a circuit race car w/a certainly wouldn't be ideal but in a street driven mr2 it has definite advantages that shouldn't be overlooked.

Can’t say I agree that it has any advantages for a street driven MR2, sure people should consider it, but for 95% of the people out there with the stock ECU, raised boost, or maybe a modified CT26, even the stock I/C is adequate. And upgraded side mount would take car of most of the remaining ones.

But since you mention it, you'd be a fool not to consider w/a in a serious drag car when you can do exactly that, fill the system with ice and get ridiculously low intake temps for just a couple of kg increase in weight.

To do it properly you'd need around 10l of spare capacity in the system, so it's more than a couple, more like about 15kgs of extra weight, though possibly it'd still be worth it if you were searching for that last drop of HP, not much use to the average punter that is still running the stock ECU though.

Now if we start talking about series charge cooling, then maybe I might be prepared to admit that W/A has it uses, but IMHO on it's own it's not the panacea that the aficionados make it out to be, especially when nobody has presented any hard data of the flow, or lack of through the side vents.

Which is why I take issue with people proclaiming that it's not a suitable for most applications. That's just another typical case of proposing a solution without first determing what the problem is, or indeed if there is any problem. This is far too common an occurence in the world of MR2's.

I prefer Air/Air over Air/Water charge cooling, it's more efficient

Do you have any data to support this? I ask as I've been asked a bazillion times which is better and I can only provide my opinion. I have fittings before and after my WTA intercooler for both airflow and coolant but still haven't had a chance to monitor any of them and get some good efficiency info.

Ahh, the thorny question of efficiency. There is an answer to this question but it's not as simple as comparing inlet/outlet temps and plotting the results, that tells you little about the heat capacity of the system and only gives an indication of it's overall effectiveness at one small point, basing a decision on such flawed data isn't a sensible approach, and the amount of data required for a decision to be made requires a lot more analysis than the average car enthusiast can cope with.

Short answer is that if there are no space constraints air/air will perform better and is the best choice unless you wish to drag race or play dyno queens in which case you can cheat by using ice water or even connecting to a tap when on the dyno.

If you want proof of air/air being better, just look at the turbo era F1 cars, the only team to try water/air seriously was Renault, and then only in series with a A/A I/C. That lasted no more that a few races before they solved the packaging problems and reverted to Air/Air. If there was any gain (no matter how small) in W/A then they would have used it.

When it comes to the SW20 then we run into the problem of lack of room for a large enough core (not lack of airflow IMO) so the situation is far from clear cut.

Efficiency as it's usually quoted for I/C's is not really efficiency at all it's a % temp drop and as such only applys at that particular point in the flow map. Efficiency as a physicist would define it is a much more useful tool for comparison purposes as it allows you to examine what would happen under varying conditions without need to map all those conditions. Such efficiency is defined as follows;

A given mass of a gas (in this case air) at temp A when combined with the same mass at Temp B will have 100% efficiency if the resulting temp is (A+B)/2. So if we assume that I/C Inlet temp is 120°C and ambient is 20°C then for the same mass of air flowing over the I/C as is flowing through it a 100% efficient cooler would have an outlet temp of 70°C.

To get to a desired temp of 40°C we would need 4 times the mass of air flowing over the core (120+4*20)/5. if the I/C was 80% efficient then it would require 5 times the flow over the core.

For a 500HP turbo engine that equates to around 1.2m3 per second, doesn't matter where to place the heat exchanger you are going to have a hard time getting that sort of flow through it so you will have to live with a slightly higher intake temp at those power levels.

An Air/Air core only has two heat transfer interfaces, air->core and core-> air. A Water/Air I/C has 4, air->core, core->water, water->core, core->air, for each interface the efficiency drops, then add in the heat added by pumping the water at pressure.

This means for the same temp drop the heat exchanger needs to work harder. As it's ultimately and air/air exchange with water as a transfer medium then you need to increase the flow over the heat exchanger core to compensate. Which increases cooling system drag and requires an even greater flow over the radiator to compensate for the increased temps (unless you mount the heat exchanger elsewhere), you also have to get rid of the extra air which can be detrimental to the front downforce if you just dump it along with the rest of the cooling air.

So if you have front mount I/Cs of the same dimensions with the same flow over the core the Air/Air will be more efficient. Depending on the mass of water the water/air system may take longer to heatsoak, but it will also take longer to recover.

Posted: Wed Jan 14, 2004 12:40 am Post subject:

--------------------------------------------------------------------------------

RunningRich wrote:

fivebob wrote:

you're this years dux from the akane school of engineering,

Do you think he will get the reference?

Probably not, but as long as he understands it's not a compliment on his mechanical knowledge it serves it's purpose, besides which he should consider himself lucky, I usually don't fire a warning shot

RunningRich wrote:

fivebob wrote:

I prefer Air/Air over Air/Water charge cooling, it's more efficient

Do you have any data to support this? I ask as I've been asked a bazillion times which is better and I can only provide my opinion. I have fittings before and after my WTA intercooler for both airflow and coolant but still haven't had a chance to monitor any of them and get some good efficiency info.

Ahh, the thorny question of efficiency. There is an answer to this question but it's not as simple as comparing inlet/outlet temps and plotting the results, that tells you little about the heat capacity of the system and only gives an indication of it's overall effectiveness at one small point, basing a decision on such flawed data isn't a sensible approach, and the amount of data required for a decision to be made requires a lot more analysis than the average car enthusiast can cope with.

Short answer is that if there are no space constraints air/air will perform better and is the best choice unless you wish to drag race or play dyno queens in which case you can cheat by using ice water or even connecting to a tap when on the dyno.

If you want proof of air/air being better, just look at the turbo era F1 cars, the only team to try water/air seriously was Renault, and then only in series with a A/A I/C. That lasted no more that a few races before they solved the packaging problems and reverted to Air/Air. If there was any gain (no matter how small) in W/A then they would have used it.

When it comes to the SW20 then we run into the problem of lack of room for a large enough core (not lack of airflow IMO) so the situation is far from clear cut.

Efficiency as it's usually quoted for I/C's is not really efficiency at all it's a % temp drop and as such only applys at that particular point in the flow map. Efficiency as a physicist would define it is a much more useful tool for comparison purposes as it allows you to examine what would happen under varying conditions without need to map all those conditions. Such efficiency is defined as follows;

A given mass of a gas (in this case air) at temp A when combined with the same mass at Temp B will have 100% efficiency if the resulting temp is (A+B)/2. So if we assume that I/C Inlet temp is 120°C and ambient is 20°C then for the same mass of air flowing over the I/C as is flowing through it a 100% efficient cooler would have an outlet temp of 70°C.

To get to a desired temp of 40°C we would need 4 times the mass of air flowing over the core (120+4*20)/5. if the I/C was 80% efficient then it would require 5 times the flow over the core.

For a 500HP turbo engine that equates to around 1.2m3 per second, doesn't matter where to place the heat exchanger you are going to have a hard time getting that sort of flow through it so you will have to live with a slightly higher intake temp at those power levels.

An Air/Air core only has two heat transfer interfaces, air->core and core-> air. A Water/Air I/C has 4, air->core, core->water, water->core, core->air, for each interface the efficiency drops, then add in the heat added by pumping the water at pressure.

This means for the same temp drop the heat exchanger needs to work harder. As it's ultimately and air/air exchange with water as a transfer medium then you need to increase the flow over the heat exchanger core to compensate. Which increases cooling system drag and requires an even greater flow over the radiator to compensate for the increased temps (unless you mount the heat exchanger elsewhere), you also have to get rid of the extra air which can be detrimental to the front downforce if you just dump it along with the rest of the cooling air.

So if you have front mount I/Cs of the same dimensions with the same flow over the core the Air/Air will be more efficient. Depending on the mass of water the water/air system may take longer to heatsoak, but it will also take longer to recover.

Confused yet. After that marathon effort I am, that's probably why Nemesis and I have been "discussing" this for the last 6 years or so, with no resolution, other than we agree to disagree

I still think series charge cooling is the way to go for the SW20 so I'm half in favour of the water/air setup I just don't like the idea of using it as the only I/C.

I'm not entirely sure what you mean here, I would have thought a datalog of intercooler air outlet temperature would provide a fairly accurate indication of real world intercooler efficiency

Not so, it takes no account of the flow over the core, was the test done on a dyno with fan assistance only, or at full speed with all fans running. Put more flow over the core via fan assistance/higher speeds or take the tests after sitting for five minutes with no flow over the core and the results will be different.

You cannot deduce from the data how much flow over the core is required to stop heatsoak and/or get the temps to the desired range. Contrast this to knowing the transfer coefficient. From this you can determine how much flow over the core is required, when heatsoak will set in, and what your likely intake temps will be if you know the flow over the core, far more useful, unless your a product marketer that is.

At a guess, I would say that the front heat exchanger of my water to air system has a frontal area at least 4 times larger than the largest core that will fit in the stock side vent. That means it has at least 4 times more exposure to fresh cooling air than a side vent mounted intercooler and is thus substantially more efficient.

Granted a front mount will have better prospects of cooling but frontal area isn't as important as surface area to volume ratio, and frontal area without flow is next to useless. Flow requires a pressure differential which means that the outlet must be at a lower pressure than the inlet or it won't work. That's where front mounts have a problem, there's already a lot of heated air to remove and the radiator is a big restriction and you don't want to exit the air under the car for aerodynamic reasons and that leaves the wheel arches or over the bonnet. The advantage is that you can fit a bigger core to cope with the lower flow per area.

Yes but your example (deleted for clarity) is based on peak hp which is also one particular point on a curve, and probably not the most appropriate point either. You are also assuming that the heat transfer coefficents are constants, which I'm not sure is correct.

Not constant, but close to it, or at least you could derive an equation for it. I chose peak HP because that's where the greatest flow is required, if the system can cope with that then it should be able to cope at all other flows.

Water has a substantially greater ability to absorb heat than air, so much more in fact as to make having twice as many heat exchange interfaces, and a possible minute increase in heat caused by pressure, irrelevant. The greater heat absorbtion capacity of water also means that the size of the charge-air cooler can be reduced substantially, allowing more efficient packaging and possibly reducing weight at the rear of the car.

It works both ways, water has 4 times the specific heat capacity as air, while that means you need 1/4 of the mass flow though the I/C core, it also means you need 4 times the mass flow at the heat exchanger, either your core has to be 4 times bigger or the flow has to take 4 times as long through the heat exchanger core, otherwise you will not rid the coolant of the excess energy and heatsoak will result.

As to the efficiency, consider this, you have an Air/Air system with 2 additional interfaces, no cooling interface has a transfer coefficient of 1 so you must lose something with the additional transfers, as the only way you can remove that heat is by having more flow over the heat exchanger or the same flow with more surface area both these result in increased cooling system drag.

I also reckon the chances of there being more flow per area at the side vent than at the front radiator inlet are as likely as Akane building a 350hp 3SGE, especially when you've got a chubby intercooler sitting in there.

IMO that show's a lack of understanding of aerodyanamic principles on your part, however in the MR2 world (actually the automotive world in general) that is very common so you are not alone. There's very good, though somewhat complicated, reasons why there is likely to be more flow per unit area than up front at the stagnation point, boundary layers notwithstanding. Hint the doors have something to do with it

Cheers

KiwiMR2