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2JZGTE - Breathing/Intercooler
Toyota designers have done a lot of work when it comes to airflow management of the Supra mkiv. A lot of this work is not immediately obvious, as it is subtle and hidden under the engine bay. Components are located in specific locations for a reason, and plastic 'bits' and 'covers' are also there for a reason. They form carefully shaped airducts so that air flows inside them with the least possible disruption.
Unfortunately not all people realise this, and they start ripping off this 'junk' in a misguided attempt to make the car lighter, more streamlined and 'improved'. Suppliers of aftermarket parts are also irresponsible, when their fitting instructions fail to mention the downsides of 'modifying' the original design the way that suits them (financially)
Front Mounted Intercoolers fit well into this category of hacks, with people paying a lot of money in vain attempts in 'improving' that are often misguided and sometimes detrimental to the overall performance of the car.
This is a schematic showing the plumbing of the standard Side Mounted Intercooler (SMIC)
It is clear that the intercooler core has a substantial shroud in the front. It fits perfectly within the front side air intake.
Back-street "tuners" look at the front-facing surface of the SMIC. It looks rather punny to them, so they disregard it as 'miserable'. Maybe Toyota was trying to cut costs, maybe they were trying to strangle the engine and stop it from producing 500bhp in stock form, maybe they didn't have a clue.
Fear not though, aftermarket wonder-tuners can fix all this, by fitting a massive FMIC right at the front of the main air intake. Apart from breathing more air (hey, the front is better than the side!) it also exposes 5 times the core surface to the airflow (more if an aftermarket front bumper is used). Surely that must be a good thing, right?
Well, not necessarily...
Take a look below at a cutout of the front radiator ducting in the supra:
The aircon condenser is sited at the front of the coolant radiator.
The intake air has no option but to pass through the cores, then it is sucked from the back by the low pressure region created by the engine undertray (not shown here, effectively it is an extension of the undercover duct)
Would these cores experience better airflow had they been sitting straight in the airflow, without the ducting and the vehicle nose?
Funnily enough, no. Despite the reduced frontal area, the airflow is superior. At high speeds, as the air molecules 'pile up' in front of the cores, the ducting doesn't allow them to overspill around the cores, which is what would happen without the ducting. The air molecules always chose the path of least resistance, and a tightly packed core is much harder work compared to bypassing it.
Also note that the sudden expansion area between the intake and the cores allow the air to slow down gradually, increasing the heat-exchange effect with the core fins (our ultimate goal)
The same principle applies with the 'miserable' intake of the SMIC. But the design of that one is even more ingenious: it further accelerates the airflow by expoiting an area of extraordinarily low pressure at the exit of the SMIC.
In order to achieve max airflow, we need a pressure difference across the SMIC core. The higher the pressure difference, the more the airflow. With the car in motion, the front of the SMIC core is at the point of highest pressure, same as the front and the other side intake. But this alone doesn't guarantee any airflow - just stick a cardboard behind the core if you don't believe it. The pressure in front of the core will be high, yes, (say 20in water) but at the back of the core it will be almost as high (say 18in water). So the difference will be tiny, 2 inches of water, leading to meagre airlflow.
The Toyota designers however exploited the fact that there is a location of exceptionally low pressure nearby, the area just in front of the wheel, and they made sure that the SMIC airflow exit path is just there. As the wheel turns at speed, it pulls with it a lot of air, especially 1"- 2" ahead of the tyre, right after the boundary layer. Remember Bernoulli: high speed --> low pressure. So the faster the car goes, the lower the pressure is at the back of the SMIC. Therefore the pressure difference across the SMIC is much higher in real life, say 20in water at the front + 15in water at the back = 35in water. That is a LOT of pressure difference, equating to a lot of airflow through the core.
Note that this cannot be replicated on a Rolling Road, the supra being a RWD vehicle and not turning the front wheels during dyno runs. This is quite a basic concept, and it is surprising how it has not been picked up by all these so-called 'experts'.
Performance of the SMIC
The people advocating the immediate ditching of the SMIC and blind faith in fitting a FMIC don't necessarily appreciate any of the above. They just put the SMIC side-by-side with a massive FMIC and see the benefits as a 'no-brainer'.
They're wrong. The choice is not as clear-cut as they think.
The job of an intercooler is to bring charge temps down to near-ambient, without creating an abnormally high pressure drop (discounting air temp difference ofcourse) and without becoming progressively heat-loaded run after run --- i.e. it should be able to shed the heat from the core quickly, so that it doesn't become 'heatsoaked' during repeated full-boost runs. Let's see how the SMIC fares in these three tasks:
1. bring charge temps down to near-ambient. This it does pretty well, as anyone who has fitted a post-intercooler gauge will know. Under stock boost conditions the charge temps don't go over ambient+10C, and even during hot summer days and operation at 1bar boost it doesn't stray over ambient+20C easily. That is not bad performance at all.
Closeup of the inside core of an old, tired and dirty SMIC.
Note how dense the turbulators are and how they overlap to maximise heat exchange. This is a well-designed core, don't let aftermarket suppliers claim otherwise.
2. pressure drop. For exact figures this needs a carefully set up rig. You cannot just stick two pressure gauges (before and after the core) expecting to see usable results. Even a theoretically perfect intercooler will register a pressure drop, since cold air has naturally lower pressure compared to hot air. The cooling effect has to be discounted. Also note that pressure drop is a function of airflow and boost pressure, so two cores might have similar pressure drops at 1bar (say 1psi) but totally different at 2bar (say 4psi vs 8psi).
Visual examination of the SMIC core and endtank design point towards a very well flowing unit, something that cannot be said for a few of the FMIC units floating around the market.3. heatsoak. This is quite important for track days because if the heat cannot be disposed of at the rate it is being accumulated, then the core will gradually become extremely hot making a mockery of intercooling and allowing 100C intake charge temps (I've seen worse)
Two factors are important here: overall mass and airflow through the core during (and after) boost.
Mass is good, because it allows the heatspikes to be ironed out saving the engine from intake temp spikes when they hurt most: under full boost. Toyota have decided to go for plastic endtanks, in their efforts to minimise vehicle weight and improve handling (mass away from the car's centre of gravity). Maybe this is acceptable for stock boost levels, but when running 1bar+ the intercooler needs all the mass it can have. Aluminum end tanks would have been better in this case. The overall weight of the SMIC is 5.2Kg which is adequate.
What the SMIC is lacking in mass, it makes up in core airflow however. It is so good that the core stays cool even after several full boost runs at 1bar. Note that this only happens in real-life tests, not in RR or dyno simulations, where the front wheels are tied down.
Naturally, all the above are true for a SMIC in good shape. A 10-year old unit that has been subjected to salt and insect damage year after year will not fare as well, obviously.
Look at the sad state of this one, it is only 8 years old but it is seriously corroded.
The rear side of the same SMIC. It looks a bit better, since salt and road debris cannot harm this side easily. The airflow through this core is lamentable, and it has to be replaced with another one.
New ones are pretty expensive from Toyota, but mercifully there are many used ones around from people who have fitted FMICs.
The best ones are from late Japanese models, young and without salt damage.
If it is not possible to source a stock SMIC in good condition, then a good alternative might be to go for a replacement SMIC.
This one is known as the 'Chris Wilson' SMIC. The tanks are made of aluminium like the stock ones should have been. Direct replacement, utilising the excellent stock location.
The core of this CW SMIC doesn't look too bad either. If anything the core inside appears to be less dense, something that would make it better suited to higher-than-stock operation, where the stock one starts to lose efficiency (dense turbulators create lots of pressure drop at high boost)
The extra weight would come handy with heatsoak.
SMIC -> throttle body pipe
This pipe is long and thick and receives all the hot air flowing away from the bottom of the radiator. As a result it is prone to heatsoaking, undoing some of the good work done by the intercooler.
Even off-boost, when the SMIC is a dead weight, once the engine has reached operating temps this pipe is hot to touch. Not good.
Thermal wrapping like this one can help protect it from the radiator heat.
Another view of this pipe. The engine undertay is missing for this picture. Once it is back in place, then the situation becomes even worse, as the hot air from the radiator has no option but to pass all around this pipe, increasing the residual heatsoak of our air charge.
Left alone this is 30-35C above ambient, depending on vehicle speed. Quite unacceptable, keeping in mind that it reaches this level without any boost pressure at all.
The fallacy of the FMIC
In the process of fitting a 'badass' FMIC the SMIC is ripped out and thrown in the bin. Then comes the painful hacking of standard parts, in order to make it fit.
The only place for a FMIC is at the front obviously, right before the aircon rad (condenser). This inevitably leads to the elimination of the upper ducting, sometimes even the lower one. The airflow through the coolant radiator has been compromised, and that is without yet taking into consideration the huge, thick core stuck in front, preheating the air and reducting the pressure difference across the core. Autos have a trasmission rad inside the coolant rad, so that is affected as well.
It gets worse. The new FMIC core now has no proper ducting, and the air can (and does) flow easily around it at higher speeds. The airpressure behind the FMIC core is not much lower than that at the front (remember the cardboard experiment? the two other rads act as the cardboard here). So the airflow through the FMIC core is not several times larger than that of a SMIC, appearances can be deceiving.
Worse still, the FMIC core sits yet closer to the bumper nosecone, without the benefit of an expansion chamber. At higher speeds it is easier for the air molecules to 'overflow' and spill outside the bumper, creating more drag and depriving the engine bay from much needed cool air.
As an extra bonus a few FMICs require the elimination (or crippling) of the active spoiler.
The coolant expansion tank has to be relocated usually, swapped for a smaller one tucked away next to the battery perhaps. Power steering pipes may have to be readjusted as well.
The FMIC can also be seen as an engine bay preheater, because that is the other side of coin. Not only does it restrict the airflow for everything else, it also preheats what is left of it.
What about parts that depend on direct airflow for cooling, like the alternator? How long is that going to live in this hotter environment?
Is it all worth it then?
It all depends on the post-intercooler temps. These are not hard to measure using an airtemp gauge. These gauges are not very mainstream, but they can be found from specialist shops for around £50. Cheaper alternatives can be had from elecrtonics shops like Maplin, but beware the very cheap ones. A sample rate of 15seconds is inadequate for such use, you need 1 second or better. Kits using K-couple sensors are better.
Before shelling out on a FMIC, it's best to fit a gauge and see how charge temps behave in real life (NOT a dyno!).
If you see charge temps exceeding ambient+20C under full boost then you know the i/c is being stressed.
If it gets progressively worse after 2-3 runs in a row, then you know that the i/c gets heatsoaked and it is overwhelmed. If the SMIC is in good condition and it still cannot cope with the heatloads, then the case for a FMIC might be stronger.
eBay FMIC inside: acceptable perhaps, but clearly not in the same leage as the stock or the CW SMICs. These vertical serfaces will create a lot of unnessesary backpressure.
Heat exchange won't be as good as the others, but since it's got more length, that could compensate perhaps.
The angle of the endtanks forces most of the airflow to the lower part of the core, leaving the upper half relatively 'unloaded'. It's still nice to have as a heatsink, but they could do it a bit better (at the expense of easy plumbing perhaps)
At 10.2Kg it's almost twice as heavy as the stock SMIC
The quality of welds isn't too bad for an economy item.
As for reliability only time will tell - in cheap cores the fins sometimes burn off and flake away on the 'hot' side of the core.
The Greddy 3-row FMIC looks a bit better inside HKS Type "S" looks even better In comparison the eBay 'hybrid' looks a bit rough (but costs a hell of a lot less)
In many ways you get what you pay for, and even if all of them are made in China, the quality standards can vary quite a bit.
....on to 2JZ GTE Crank Ventilation
Here are some hints on using intercoolers from different kinds of vehicles:
A huge, thick and dense intercooler might be good for a big, slow earth mover, but won't do a 150mph car any favours.
This is a closeup from a large diesel truck
The turbulators inside the air passages are not too bad, although they would be much more efficient in a low-speed, high air volume application like the one they were designed for. As mentioned before, there is an optimum airspeed for efficient heat exchange, and that stands for both internal and external airflow. If the external (cooling) air moves too fast or too slow (for the turbulators) then the cooling function can be reduced considerably. Same with the internal airflow, that can be almost supersonic after the compressor. An intercooler meant to be on a 200cfm engine (say a diesel) will experience extreme airspeeds if fitted on a 600cfm engine. Not only will heat exchange be rubbish at full boost, but there is the risk of internal turbulators breaking off and there is only one way for them to go: through the engine.
In the tube and fin cores, tubes are more expensive to manufacture than fins. So an el-cheapo core will be mostly fins and short on tubes. This will give the impression of VOLUME but pressure drop will be high and heat rejection low. The rest of the engine bay will be deprived of fresh airflow for no good reason!
The endcaps are very important - sloppy and angular designs are cheap to manufacture and buy, but they flow badly, and they might not spread the airload evenly through the tubes (increasing backpressure for no good reason). The endcap right after the compressor is a bit more important, as the air will be very hot and very fast and it has to turn AND split into different passages. The FRONTAL section of the inner core is very important too, as that's what the ultrahot air first 'sees'. If the surfaces are sharp and vertical they increase backpressure with no added benefit. However the internal turbulators are meant to upset the airflow so that it swirls and hits the edges of the tubes giving up energy. That's why it's important to look at a section of the core before the endcaps are fitted.
Bar and Plate core designs are considerably more rare and expensive. I don't think they're worth the extra money in an application like this. They are better when space is severely limited and every drop of intercooling efficiency is essential (say on a motorbike)
My first choice for a replacement OEM intercooler would be from an engine of similar displacement and power as the one I'm building. That's why I floated the idea of the EVO intercooler some time ago, and it has caught on. I remember being at Power Engineering (Uxbridge) and they had 3 stock EVO intercoolers piled aside because their owners bought bigass aftermarket ones. I felt that they would go for peanuts, keeping in mind that they are proper designs, unlike the Vauxhall jokes.
Here Simon Morris displays an example of fitting an EVO intercooler onto a Calibra.
Here are the steps for fabricating an intercooler capable of flowing 1000Hp (twin turbo Corvette)
Custom single intercooler for a twin-turbo application, courtesy of toohighpsi. The two opposing inlets are not allowed to mix too much - compact and nicely executed.
Leaving the stock intercooler as well
In a nutshell, NO
Heat exchangers operate with maximum efficiency when the temperature differences are large. When the turbo chunks out air at 150C and the ambient air is at 10C, that's a 140C difference - the intercooler operating at (say) 70% efficiency will reduce the temp by 70%*140C= 98C.
But if the compressed air is at 30C the difference from ambient (10C) is just 20C. The efficiency now is much lower, below 40% perhaps, so this same intercooler will only reduce the temp by 40%*20C = 8C. Still, 2% power increase, but the extra pressure drop will take some of this back.
This is always the case with intercoolers (or chargecoolers) connected in series. They both share the same ambient air temp, but the first one in line experiences the large temp difference, and does 80% of the work. The next one breathes in the cooled-down air, and can only bring a modest improvement - but it doubles the pressure drop nevertheless. (Strictly speaking it only doubles the flow resistance, because the pressure drop also depends on temperature, but let's keep it simple here).
So it's not a good idea to fit a massive FMIC and keep the old chargecooler or the stock i/c connected as well. The chargecooler would be less of a problem actually, as it flows much better internally, but it's efficiency would still be greatly reduced, and all that weight and extra piping may not be worth the aggro.
According to Ali-G the rapper-tuner, there is only one colour for a heat exchanger, and that is
BLACK.
Not silver, nor chrome - but matt black. Shiny surface externally is not a good thing (doesn't catch the incoming air), neither is a thick coat of paint (insulates)
But if the intercooler is situated inside the hot engine bay, then the black colour will aid heat exchange you'd rather avoid - it will be more of an 'interheater' - but then colour is the least of your problems...
Copper has superior heat transfer properties, why don't we use copper cores? Good question.
The story goes that copper cannot take easily the pressure and heat stresses from a couple of bar pressure and 150C at the same time. It would need to have much thicker pipes to compensate, but that would reduce the heat exchanging capabilities to the point where it's worse than an aluminium core of the same external size.
I wonder how it would be to have a steel (or aluminium) frame, with a copper core inside. The external frame would provide the structural integrity and flex-resistance, and act as an auxiliary heat sink as well. The copper core would then focus on pure heat-transferring tasks. Maybe a project for the future.
Here is a lot more on the automotive use of copper
On very hot days, the intercooler core will obviously be quite hot, and we know that it's impossible to cool the charge below that temperature. In fact we can't really cool it even at that temperature, efficiency can never be 100%
But if we get a bit creative with the cooling medium, we can go one step further. A well-known technique is spraying water onto the intercooler core. If the core is hotter than the water, then some heat will be absorbed above and beyond that absorbed by the incoming air cooling stream. However at high airspeeds water just won't stick to the core's turbulators, so it won't do much for power.
The water needs to be sprayed as a fine mist - it will then be able to stick on the core, having a better chance to absorb some heat. The water injection nozzles have to be carefully positioned, too. A spray that hits the middle of the core with the car stopped, might only wash the headlight as the car is moving at 70mph.
Other cooling media have been tried during futile attempts of further cooling down an intercooler. Even compressed CO2 is being touted as the king of intercoolers sprays, in the from of the N-tercooler
Alcohol seems like a good liquid to use, with a low boiling point and easy evaporation. Unfortunately real-life tests have proven otherwise.
A test-rig can be setup to test various attempts to increase efficiency of an intercooler core.
This one uses a powerful heatgun to simulate the hot air exiting the compressor.
Although temperatures are approximated, the total airflow is nowhere near the real thing.
Checking on the temperature of the exiting air we can get an idea of the efficiency increase from the various intercooler sprays. Reality is a bit more brutal - with a good setup, the bestl you can do is increase the intercooler's efficiency by 10%. That's not 10% more power unfortunately, but 10% more of the extra power boost given by the intercooler. So if the intercooler is responsible for 60bhp, it will now account for an extra 6bhp (while the spray is operating). Kits spraying NO2 are more effective while running (skyline and supra owners testify to this) but they are very wasteful on gas, compared to the modest power increases. Nitrous is meant to be injected inside the intake!
Not too impressive, but on a hot day every little helps!
Here is more on Chargecoolers
Here is a Water Injection setup on the LET
Finally...
To get an idea of the temperatures and efficiencies blend together, here's a handy little calculator I prepared earlier. It is unique in the business and comes in handy when tuning on the edge. This is the basic version and doesn't cope with water injection or NOS. Still, very handy indeed.
Some hardcore intercooler theory for those who can't be satisfied easily.
Fabricating your own intercooler is possible (but not too easy though) (local copy here)
Good reading on Water Injection, scooby alcohol injection here
An American site for one of the first production turbo cars (Buick Regal)
If you think that cooling the air is the only way forward, see how heating it up can make even more power
Mathematical analysis of aircraft intercooler design from the NASA archives
On to the Throttle body...
To be more accurate, it is not just the 'psi' value that is important, rather
the airflow and air temperature needed to be tackled.
A big single is likely to produce cooler air exiting at 18+psi, compared to stock twins.
There is very good ducting around the SMIC which is totally lost when moving to a FMIC
There is also good ducting around the aircon condenser and coolant rad, which is typically hacked and compromised when fitting a FMIC.
The warm air from the outside of the SMIC core goes away from the vehicle immediately, while the warm air from the FMIC goes straight into the core of the coolant rad, and then into the engine bay.Also the pressure difference across the typical FMIC core is much lower than that of the SMIC core, so it's deceptive when you compare core sizes.