235 | Choosing an Intercooler for your Build
Compressing the inlet air into the engine naturally increases the air temperature but unfortunately heat is the enemy of power because it is less dense. This is why inter cooling is common place on almost every forced induction engine but not all intercoolers are created equal. In this webinar we’ll discuss the different options available, what to look out for and what considerations you should be making when designing an intercooler installation.
- Hey guys, it's Andre from High Performance Academy here, welcome along to another one of our webinars. This time we're going to be talking about some of the options that you'll need to consider when you're selecting an intercooler for a forced induction build. This might seem like a pretty simple task but there's actually quite a bit to take in. So we're going to be talking about the different styles of intercooler that are available, the pros and cons of those different styles, as well as a few subtle tricks that I've picked up over my career tuning turbocharged and supercharged engines to help make sure that you're selecting an optimal option for your particular car. It can be expensive building an intercooler setup so it's not something that you necessarily want to be doing twice.
As usual we will be having questions at the end of the webinar so if there's anything that I talk about then please ask questions at the end, if you'd like to know more, or anything just generally related to this topic. So we're going to start with some real basics which I'm going to assume that everyone watching will already understand but we need to cover this off just so we're all starting on the same page. And that is why we need an intercooler. Simply put, when we compress air via either a supercharger or a turbocharger, we're naturally going to increase the temperature of that air. This is basically simple physics, we can't get around it.
Made worse though is that depending on the turbocharger or supercharger that we are using, each type of compressor will have a certain efficiency and particularly if we are pushing maybe a turbocharger really hard and it's working harder than it should, it falls out of its efficiency, what that's going to mean is that pound for pound of boost, it's actually going to be adding even more heat into the air. So of course the problem with adding heat into the air, there are a couple. The first one is that hot air is less dense, this means for the same volume of air, we have less oxygen contained within it and of course it's the oxygen that really dictates how much power our engine can make. So hot air, naturally then is the enemy for power. We want to try and reverse that, cool that hot air down and increase the air density before it enters the cylinders.
This way we will end up producing more power for the same boost pressure that we happen to be running, that's where our intercooler comes in. Now another subtle aspect here that's important to understand as well is that anything that we do that increases the charge temperature inside of the combustion chamber, can have the knock of effect of making an engine a little bit more prone to suffering from detonation. So this can be really damaging, particularly if we don't have all of our compensation tables dialled in for perhaps air temperature correction for our ignition timing, then at very high air temperatures, we may actually find that our engine starts to suffer from detonation or knock which can very quickly destroy the engine. So basically these are the reasons why we're going to want to add an intercooler. The idea of the intercooler, essentially regardless of the type of intercooler we are running, is just to cool that charge temperature down so that we're increasing that air density.
So what are our options when it comes to an intercooler? Well the first and probably easily the most common would be the relatively standard air to air intercooler like we've got sitting here. These in general will be mounted somewhere in the front of the car where they're exposed to the airflow, the idea behind them is that simply our charge air goes through the internal fins inside the intercooler, our ambient airflow flows through the other side of the intercooler and we get a heat transfer. The heat from our charge air is transferred into the aluminium and as the ambient air flows through the intercooler, it basically reduces that temperature and cools back down the aluminium, so it can continue that process. So these are relatively effective, we'll talk a little bit more about their pros and cons shortly, they've been around for a long time and they're relatively easy to understand. The other option that we've got is to look at a water to air intercooler.
And there are a few options when it comes to water to air so let's have a look over at my laptop screen. We've got a couple that are a little bit out of the norm but we'll cover them off anyway. So this is a water to air intercooler on the front of the Titan Motorsports Supra drag car. So what we can see here is we've got the turbo setup, we've got the charge piping that leads around here and then we've got a large intercooler core. So the idea here, it's very similar to an air to air intercooler, except that rather than using ambient airflow as a cooling medium, we're passing liquid through the intercooler.
Actually generally the way the intercooler is arranged, it's the opposite to how our air flows in an air to air but essentially the premise is the same. We then have air cooled coming back out into our plennum chamber. I've got another example here, essentially the same sort of deal. This is on an R35 GTR drag car. The turbochargers are mounted in the stock location so we can't actually see them but we have a large water reservoir here and we've got our intercooler cores in here.
So essentially exactly the same thing. Now the two applications that I've just shown you are very specific to drag racing. So for this reason, because the car's only running for perhaps six seconds under high boost, we don't actually need to worry about getting the heat back out of the water, so it's run as a system where the water is probably going to start the run with ice in it, so it's going to be cooled down, we're going to get as close to 0°C as we can with our water. That's going to be pumped through the intercooler and it does, in this way it's very very effective. But of course as the car goes down the drag strip, that water in the reservoir is going to become heated.
So we can't end up running a car around a racetrack or out on the road with this sort of system, so with most water to air intercoolers, we'll also incorporate a pump that's going to pump water through the intercooler and then it's going to pump it through a separate water to air radiator that sits at the front of the car. So in this way there is a little bit more complexity. We'll actually have a look at another system here, that is the worst photo in the world but I'll just blow it up a little bit so we can see, no that's not the one I wanted. That's not going to help me, let me just get this back down to the normal size. Here we go, so this is a GM supercharger setup with an water to air intercooler that sits down in the valley.
This is really common on a V configuration engine with a supercharger because the supercharger tends to conveniently sit in the valley and it can be quite difficult to integrate an air to air intercooler with this sort of system. So this is the heat exchanger that sits inside of the valley there, the supercharged air, the heated air goes through that intercooler and then we can see that on the end here we've got a couple of water hoses. So again I haven't got any photos of the radiator that sits at the front of the car but hopefully you can understand that it's pretty self explanatory, it's just going to be another water to air core and that's going to be located in the ambient airflow so it's going to kind of work a little bit like our air to air intercooler. Alright so we've dealt with air to air, we've dealt with water to air. I'm going to deal with one more aspect 'cause I think it might come up in the questions and it's not really a type of intercooling.
This is water methanol or methanol injection. And I think that's possibly dropped from favour a little bit these days and I don't mean that no one runs water and methanol injection but this has been used in the past as a replacement for an intercooler. It can be effective, it's certainly more effective than running no intercooler at all. The idea behind this is that by injecting water or water and methanol into that superheated air coming out of the turbo or supercharger, what we'll find is that the water or methanol as it goes through a phase change from liquid to vapour will absorb heat from the combustion charge as it goes through its phase change from liquid to vapour so it absorbs that heat and it cools down the charge temperature. Again I don't think I could consider this as a worthy replacement for an intercooler even though it might help remove some weight from the vehicle.
You're also at the, you've got the problem there with water methanol injection that if your tank of water and methanol runs out, then you've got big problems because you're going to end up with super heated air going into your engine and that may be difficult to account for from a tuning perspective. Last category I'll just talk about here, and and this is not really intercooling but it's worth just discussing briefly. Again we'll jump across to my laptop screen and this is the engine bay of Colin Wilshire's Jett Racing Mitsubishi Eclipse. So depending on when you're watching this, this may or may not be currently the fastest four cylinder drag car in the world. Regardless it is incredibly quick.
And last time I saw a dyno graph I think this engine was up around 2000 horsepower which from a four cylinder engine is no mean feat. Understandably that relies on running huge amounts of boost pressure. Again probably subject to change but last time I talked to Colin I think he was well north of 100 psi. Despite all of that, you'll notice that this is the outlet from the turbocharger here, this is the charge piping, it runs around here straight into the throttle body. There is not intercooling included in this particular car.
And I quite often get asked why this is the case. The reason for this is that a lot of high boost turbocharged, and supercharged drag engines will run on methanol fuel. And methanol gives us a bit of a free kick in terms of intercooling. There's a couple of reasons for this. First of all, methanol when we are running on methanol fuel compared to pump gas, we are using a huge amount of fuel.
To make the same power on methanol compared to pump gas, we're somewhere in the region of about two to 2.5 times the amount of fuel by volume so you are literally pouring the fuel into the engine. The other thing is that methanol has a very high latent heat of evaporation. I've touched on this already, essentially it just means that when we are injecting the fuel, it's drawing a lot of heat out of the combustion charge temperature as it goes through that phase change from liquid to vapour. So even though the air temperature entering the throttle body on this engine could be incredibly hot, the fact that it's running so much methanol and that latent heat of evaporation actually allows us to get away with this. Now again this is a little bit off our topic but I just wanted to touch on it and we do see a couple of schools of thought.
There are some incredibly fast methanol powered drag cars that run no intercooler such as Colin's here, we'll see some equally powerful and fast methanol powered drag cars like our Titan Motorsport Supra here and George's R35 GTR from T1 Race, that run on methanol fuel but do choose to use an intercooler. And actually I'll just try and find my photo, if you just give me a moment here. If we jump across to our Instagram account here, this is actually a photo of my old drag car, this was my old shop car and this is a methanol 4G63. Personally, even though I was running on methanol, I actually prefer to use an intercooler. I felt that this gave me an advantage in terms of more consistency in the air temperatures.
So I was using a PWR barrel intercooler here which you can see. Basically straight off the outlet of the HKS T51R SPL turbocharger. And again we pumped an ice slurry through that intercooler. So this just meant that as we left the line through to the end of the drag strip, eight odd seconds later, I could be pretty confident that my air temperatures were going to be pretty consistent whereas we're going to see quite a large increase in air temperature without that intercooler. Again, having said that, we are talking now about using intercoolers.
I just wanted to touch on that because I know that it's a topic that comes up quite regularly. Alright so let's talk about our considerations for the type of intercooler that you should be running. The first one we need to consider is the packaging or installation in the car. The reason for this is that an air to air intercooler such as this one we've got here, simply might not be possible in every installation. Particularly in a lot of mid engine and rear engine applications, physically getting airflow through to an air to air intercooler can be tricky, in some instances it can be impossible.
If you're running a conventional front engine car then an air to air intercooler shouldn't be a problem, wouldn't be too many applications where you can't fit an air to air intercooler in a conventional front engine application. Beyond that, we also need to think about the effectiveness of the intercooler. And what I'm talking about here is how efficient the intercooler is. In other words, how close can we get the charge temperature to the ambient temperature of the air flowing through the intercooler or in the water to air intercooler case we're obviously relying on a cooling medium. So basically how good a job can that intercooler do? How much can we drop the temperature from the compressor outlet before it goes into the throttle body? Now there are two factors to consider there, there's the efficiency but the other side of this is that we could produce, or the manufacturers of intercoolers could produce an intercooler that does a better job of dropping the air temperature by using more internal fins and giving a more complex flow path so that there's more heat transfer going on.
This can actually end up creating more pressure drop in the intercooler and that's something we don't want as well. The pressure drop, simply put is the difference in the pressure from the turbo side, let's say we've got our turbo feeding air into this side of the intercooler. So if we measured 20 psi at the intercooler inlet, and on the other side of the intercooler we measure 18 psi, what that means is we've lost two psi across that intercooler. It's the pressure that's going into the engine that matters but also what it means is that this creates, when we're got a pressure drop, it means that we're actually driving the turbocharger harder, we're working a different area of the compressor map compared to what we'd actually think if we were purely looking at the boost pressure in the inlet manifold so it's something that a lot of people don't monitor but it can be quite an important consideration and particularly if you're starting to see the pressure drop increase beyond two to three psi, that probably means that you're leaving quite a bit of potential performance on the table. We also need to consider the size of the intercooler.
Within reason, if we're talking about an intercooler core either air to air or water to air, it's hard to generalise too much but in most instances, larger is going to be better. There can be some packaging issues with this though so generally what we can fit into the car is going to be dictated by the room we've got available. Of course as we add to the size of the intercooler core as well we are increasing the air volume in the intercooler as well as the intercooler piping and that can be a consideration for turbo response and lag, we'll talk about that though as we get a little bit further through this. So these are our main considerations, the other one though is complexity and this really comes into if we are bargaining between, weighing up between an air to air intercooler and a water to air intercooler. The water to air intercooler definitely is going to add to our complexity provided we are going to need a pump and a cooler core.
If we're running a drag style system with an ice slurry then that's possibly not such a big consideration. Alright we'll get into the air to air, I'm going to deal with that first because obviously this is the most common style of intercooler that we are going to get. And what I'm going to do is I'll just cycle through so I can see a couple of photos. So the two main types of intercooler or the two types of intercooler core that you'll probably hear discussed are bar and plate and tube and fin. And there's pretty intense debate on the pros and cons of both or either and which is the best.
Just so we know what we're talking about here, this particularly intercooler is a bar and plate style intercooler. You can normally tell because the passes through the intercooler are quite square. And if we jump across to my laptop screen for a moment, this is a tube and fine style intercooler and we can see here the passes through the intercooler are kind of oval at the end so that's kind of one of the hints that we're looking at a tube and fin intercooler. I'll just cycle through, I think I've got another shot, yeah if we have a look here as well, on my laptop screen, this is a side shot, so looking in through the side of the intercooler for a bar and plate style intercooler. So first of all, advantages of the bar and plate.
So this could actually be seen as an advantage and a disadvantage. One of the advantages is that the bar and plate intercooler is going to end up normally being quite significantly heavier, there is more mass of aluminium that goes into the design and construction of a bar and plate intercooler. Now it might sound strange that I'm calling that an advantage when obviously weight's something we try and get out of our cars. However how this works is that initially when hot air enters the intercooler, we don't instantly get heat transfer from that hot air out to the ambient airflow. Instead what initially happens is that the heat is actually absorbed into the aluminium material.
So a larger mass of aluminium kind of works a bit like a heat soak. So it kind of tends to quickly absorb that heat. Of course over time it will expel that heat to the ambient airflow. Whereas the tube and fin intercooler, the passes are a little bit thinner, there's a little bit less material there so the intercooler is lighter but of course it has less of that heat soak capability. Now personally I'm on the fence here because I've used both tube and fin intercoolers and bar and plate intercoolers, I've had really good results with both and I could not stand here and pick a winner.
I could not say to you that you must run a bar and plate or a tube and fin intercooler. Instead, I think there's actually some much bigger considerations. Particularly these days when we're seeing more and more cheap intercoolers coming onto the market from Chinese manufacturers, in my opinion the style of the intercooler design is probably less important than some of the internal construction. So let's head back to my laptop screen and I'll show you what I'm talking about here. So again, this is the photo we've already looked at, this is the end of our tube and fin intercooler.
So these passes through the intercooler as we can see here, this is where our hot air flows. And these aren't open passes, as you can see, they're a little bit like the front of the intercooler, we've actually got these internal fins. And this is important because it creates surface area inside here and this creates more area for the charge air to contact and to dissipate its heat into. So we actually want a reasonable area of fins. This comes back to what I was saying before though.
It isn't a case of more is better, we get to a point where we've got such a high density of these internal fins, we're going to actually create a restriction to air flow and this creates a pressure drop. So there is a happy medium here. However, this is kind of not what we want to see here. This one here where we've got this really open design, we haven't got a very high density here of the fins. This is another one here, again a slightly different design but not a lot of density in the fins.
So this is reducing the amount of heat transfer that can occur. On the other hand, this is kind of what I like to see when I'm looking into the end of an intercooler. We've got a high density of those internal fins inside of this intercooler and that's going to allow the intercooler to do a good job. Now I'll bring this back to a real life experience that I had. When I ran my old shop for a period of time up in Wellington, we dealt obviously with a lot of turbocharged cars and we built a lot of cars from the ground up.
Obviously intercooler upgrades for a stock car is a pretty common upgrade path and we had a supplier who was bringing in Chinese intercoolers, the conventional 600 x 300 mm intercooler that's kind of the staple of the two litre to three litre engine capacity when you're building a fast street car with the three inch or 76 mm outlet. That's kind of the staple diet of the intercooler upgrade world. Now we'd been using those intercoolers from the same supplier for probably a period of about four or five years. They were pretty good quality, they were well priced and they did the job so again for that street level customer, it was a perfect option of cost versus benefit. What we found though is that all of a sudden we were getting these same intercoolers or theoretically the same intercoolers, the shop or the manufacturer I should say over in China had changed suppliers or changed their processes and all of a sudden we were starting to get these intercoolers in that had these very open passes internally.
And this is something that's very easy to overlook, you may not even take any notice of what's inside of your intercooler. But what really drove this home for us was a turbocharged Subaru GC8 STi that we had on the dyno. It was producing around about 300 kW at wheels, 400 horsepower at the wheels but we were really struggling with air temperature, after a single pull on the dyno, the air temperature in the inlet manifold was climbing up to about 75°C which is absolutely huge. And if you did a run back to back the air temperature just continued to climb and the power was just plummeting as a result. Suspecting that there was a problem with the intercooling, my tuner at the time pulled the intercooler off and inspected the internal passes, and again if we can just jump back to my laptop screen, it was actually a little worse than what we're seeing here.
If I remember correctly we probably had about half the number of fins as what you're seeing there so there was just none of that internal finning to get rid of the heat. So swapping to another intercooler that we had on the shelf from an earlier batch that had all of the internal fins, straight away the air temperatures were under control, we were seeing about 35°C at the end of a run and the car picked up around about 40 kW at the wheels which is over 10% power at the point we were at. So just understand that not all of these intercoolers are created equal. And we're actually seeing more and more of these intercoolers, probably because they're cheaper and easier to manufacture, that don't have the internal fins. So just make sure before you actually spend your hard earned money, and this really goes for any intercooler core, whether it's air to air, water to air, make sure that you are actually getting a quality core.
You can, if you are building a custom intercooler, you can circumvent this and make sure that you are getting a good quality core by buying from the likes of Garrett or Spearco, some of the big names in intercooler construction. Alright so we've talked about bar and plate, you've got my opinion on it, the actual internals of the intercooler are more important. I will mention one of the other often stated disadvantages of tube and fin is that because the passes through the intercooler are normally relatively thin, they can be a little bit weaker and a little bit more prone to damage from debris. Now that might sound a little bit unlikely, I actually did have a tube and fin intercooler fail on me many many years ago in one of the project cars because it was pierced by a stone. Problem with this is that it's essentially completely impossible to repair as well.
Everything's so thin and the proximity to all of the fins makes it basically impossible for a welder to do a good job of welding those up. On top of that, we do also need to consider the way the intercooler is going to be mounted. The two usual options there are V mount or to front mount. I'll just jump across to my laptop screen again for a moment. This is a shot of our FD RX-7 project car.
And the FD RX-7 makes it a little bit difficult to fit a front mount intercooler because the nose of the car is quite shallow, there's not a lot of room in the front of the car and particularly if you do want to fit a sizeable front mount intercooler then almost certainly you're going to have to do some trimming to the front bar. With this particular car we didn't want to do that so despite the fact we actually started by buying a front mounted intercooler kit we actually went to the trouble of having a local fabricator up the road from us Vinny Fab produce this V mount kit. So as its name implies, this essentially mounts the radiator and the intercooler in a V configuration. As with everything, pro and cons. There is nothing that's absolutely perfect here.
The V mount does give us the advantage of being able to fit a larger core because we're leaning that intercooler back over. There are some people who will claim the V mount gives them advantages because the volume in the intercooler and plumbing tends to be shorter because the intercooler plumbing is shorter. As we'll find out, I don't necessarily buy into that being an absolute game changer. One of the biggest things with a V mount configuration though is understanding that we need to make sure that all of the air goes through the intercooler. So it's not enough just to V mount the intercooler and radiator, we actually are going to need to build some baffles or guide plates to make sure that the air goes through the core, air's kind of lazy, takes the path of least resistance so if it's got a way to go around an intercooler, it's definitely going to do that.
The other aspect is making sure that we can get air out the back of the intercooler and in the perfect world, what we would probably want to do is duct this up through the hood or bonnet so that the air goes back out into the air stream over the car. Again, with this car, we don't want to cut up the bodywork so we're not going to do that but it's something we understand can be a sacrifice. Regardless whether you're going to go V mount or front mount, those same guides stay in place there, make sure that the air is forced to go through your intercooler, so it can require you to make up some baffles or some plates to direct the air. You want to seal all of that to the intercooler core to make sure everything goes through it so the intercooler has the best change possible of working. The other thing to understand there is that a large front mount intercooler can end up, or by necessity is going to end up reducing the airflow or affecting the airflow into the radiator so if you've got a car with a cooling system that's already marginal, putting a large intercooler directly in front of that radiator probably isn't going to work too well so this all comes down to sizing your entire cooling system, it's not just the intercooler that you need to consider.
Alright so we've talked about air to air, this is probably going to be the most common as I've already mentioned but let's jump into our water to air option. We are going to go into some questions really shortly, I've already seen there's a few in there, so if you've got any more questions, please continue to ask those. So with our water to air, most people who are proponents of the water to air intercooler will, and quite rightly say, that the water to air intercooler has the potential to be more efficient. But there are a couple of things we need to consider with this. That might work really well in our drag application where we aren't trying to get the heat back out of the water.
We can do a better job of drawing the heat out of the intercooler and getting it into an ice water slurry. However for a road or a circuit application where we need to run lap after lap or a long extended period of time, we need to obviously get the heat back out of the cooling medium. So this requires our water to air radiator that's going to be placed in the airflow at the front of the car and it also requires a pump to pump that through. So the problem, at least in my experience is that we've now got two areas where we've got heat transfer. We've initially got the heat transfer from the hot charge air into our intercooler that's in the engine bay, maybe in the inlet manifold and that heat then needs to make its way into the cooling medium.
The second path though is we then need to get that heat back out of the cooling medium. So you've kind of got these two problems here. First of all, the coolant that we're going to be using, there's no way obviously we're going to get that down below the ambient temperature so there's going to be a situation where our coolant, by necessity is going to end up some temperature higher than our ambient airflow and likewise when it goes through the cooler core in the engine bay, we're also going to find the same situation, we're not going to get our charge temperature down below what the coolant medium is at so in this instance, we generally find that all things being equal, we're going to end up with a higher charge temperature with the water to air intercooler than an air to air. The other issue is of course complexity. We've got a lot more moving parts in the system, we've got a lot more area where things can go wrong.
So you do need to factor this in and a water to air intercooler setup is also going to usually be quite significantly more expensive. That being said, there are instances where I think a water to air intercooler, when it's well designed, does make a lot of sense. One of these would be a mid engine'd car where it can be very tricky to get good airflow to an air to air intercooler core and this way we can run the water to air core in the engine bay and then we can just plumb the water forward to the front of the car where it can be placed in ambient airflow and get the heat out of that coolant. The other instance is, which we've already touched on is where we are something like a V8 with a positive displacement supercharger mounted in the valley, in this instance it's almost impossible to run the charge air forward to a air to air intercooler so the water to air intercooler's a nice solution there because it fits down below the supercharger right in the valley, keeping the flow path as short as possible. Now this brings back to the other issue that I just want to touch on as well, is a shorter path and less volume in the intercooler system really that critical? And I did a test and this is many many years ago, I'm going to admit it wasn't the most scientific test, it was back before I had a dyno and I had a front wheel drive Toyota AE82 Toyota Corolla for those of you joining us from the U.S., I don't know if you got those over there but anyway it was fitted with a Toyota 4AGZE.
So this is their factory supercharged engine. And in stock form, these actually run a top mounted air to air intercooler, so generally a bonnet scoop will flow air through that. So this is a relatively short flow path and I know it's not a water to air intercooler but the same sort of effect. We ended up with probably no more than about a foot and a half or two feet of plumbing and the volume of the end tanks of the intercooler was relatively small. We did have trouble with air temperature in that particular car, it was hard to keep the air temperature cool, particularly when we increased the boost.
So one of the modifications I made to the car was to fit a front mounted intercooler. At the time I had a Mitsubishi Lancer Evo 2 intercooler. We front mounted that, physically a much bigger intercooler. We probably ended up with the intercooler plumbing going from about 1-2 feet, probably up to 6-8 feet. I made sure that the plumbing diameter was relatively small but understandably we're adding a great volume of air to the intercooler system.
Despite that massive change I made, I actually couldn't tell from the driver's seat any difference in terms of throttle response. And this is something that sort of followed me through the modifications we've made to various cars over the years. I generally don't see the massive increase in lag or throttle response that a lot of people claim when adding volume into the system. Now obviously this doesn't mean that we're going to make the plumbing bigger in diameter or longer than it needs to be, there's no sense in that. But I think, just in my opinion from the number of cars that I've personally modified, the results we see, the drivability et cetera, I think it's something that maybe people put a little bit more emphasis on than is truely needed.
So there you go, that's, in my opinion, the things that you should be considering when you are looking at an intercooler system for your next build. We'll jump into our questions and see what we've got, if you've got any more questions, please keep asking them. Adan has asked, would using a water to air be good for a three hour endurance race or it's not that efficient? So I've probably answered some of these questions really, so it's not that it's not efficient, it's just we've got those two heat transfer mediums from the charge air into the cooling water, from the cooling water back to into the ambient airflow. For our purposes, I'm guessing this is the angle you're going with, for our purposes for an endurance race, I wouldn't probably want to choose a water to air intercooler because we've got a front engine'd car. If we turbocharge that, we've got a relatively short path to run our intercooler plumbing, it's relatively easy and it reduces tha complexity, particularly for endurance racing we want things to be as simple as we can make them.
Noah's asked, do compound turbo engines running eight to nine atmospheres typically fail by heat or mechanical failure if coolers are correctly chosen? OK pretty complex question, probably a little bit outside of intercooling specifically but generally the reason someone's going to be running a compound turbo system is to multiply the boost pressure through the turbo system and allow efficiency at a higher manifold pressure than what you could run with a single turbo. So by definition then they're going to be targeting very very high specific boost pressures in the inlet manifold, this results in very high cylinder pressures so it puts a lot more mechanical stress on the engine. So I can't really say with certainty here, I would say mechanical strength is probably the biggest consideration but intercooling and getting the heat out of the engine is also very very important. A lot of the compound turbo setups we see are on diesel engines although earlier in the webinar we did look at Colin Wilshire's compound turbo Eclipse running on methanol, obviously with no intercooler. I dunno, take from that what you can.
We've got a few questions here, a little bit similar, Adan has asked, have you guys ever looked into using air conditioning to cool incoming charge air from the intercooler, what are the applications of an intercooler connected to the A/C loop? Alright yeah so basically a whole bunch of questions from Adan, Vikrant and Timothy about using air conditioning. OK the problem is that what we need to understand with air conditioning is that it actually saps a significant amount of power from the engine in order to produce that cooling effect. So it's going to depend from engine to engine, a good example of this was locally here in Australasia, there was recently a 12 hour endurance race for GT3 style racecars held at Mount Panorama or Bathurst. And for this generation of GT3 cars, they now legally have to be fitted as I understand it, with an air conditioning system. Talking to one of the drivers in an AMG SLS GT3 racecar, they said that they were losing around about 4-6/10ths of a second per lap if they ran the air conditioning and I think again if my memory serves correctly, they were claiming a power loss of around about 40 horsepower so it's not insignificant.
So that would need to be considered, basically are you gaining more power than you are losing? There was a system, I don't know if it still exists, which was a Nitrous Express, no it's not Nitrous Express, it was a nitrous system, oh Zex I think it was, and basically they had a spray bar that sprayed nitrous over the intercooler. We actually tested that through my old shop, incredibly effective, it works really really well but unfortunately also a fairly short lived result. Obviously you're going to empty a 10 pound bottle of nitrous pretty quickly and at least here in New Zealand, nitrous is ridiculously expensive so not maybe an option. Thomas has asked, should you always see a pressure drop if the air is colder? You will see a pressure drop across an intercooler core, basically no matter what the air temperature is and no matter how efficient the intercooler core is. It's just an aspect of the design.
Generally you can get that pressure drop down below 1 psi at which point it probably becomes negligible in its total effect. Thomas has asked, how come they don't serpentine the path as with oil coolers? That's a good question, I'm guessing what you're talking about is the airflow through the core. I mean with an oil cooler, what we generally do is run the oil down so it's more like a vertical system, the oil will run across and then back up. What I would suspect with that is with an intercooler, that's actually going to end up basically creating more pressure drop. Basically anything you do that makes the air turn corners or makes its life harder is going to end up with an increase in pressure drop.
One thing I will actually focus on with this though, 'cause this is something that comes up and I think it's maybe worth talking about, is that with an intercooler like this we see that the inlet and the outlet are basically inline at the bottom of the intercooler. So what this can mean is that internally there's, unless you've got a baffle or a guide plate, you're probably going to find that the predominant airflow will be along the lower side of the intercooler and we may end up with less of the air at the top so it can be a good idea to either use a guide plate to help control some of the airflow up the intercooler or alternatively if your installation will allow it, you can mount one end tank with the inlet at the top, the outlet at the bottom so that's quite helpful. Raddi has asked, similar question here, what are your thoughts on a dual pass design intercooler? This is really going to come down to packaging I think. I don't think it's a necessity. If the packaging allows it then there's probably nothing specifically wrong with that, it's more a case of allowing sufficient area in terms of the surface area of the intercooler for the air to flow through as opposed to how we flow through it and then it comes back to the last question from Thomas, if you make the air try and go through a 180 degree turn or do something really nasty, it's not going to really want to do that so you can end up with an increase in pressure drop.
Next question, on a twin turbo setup, is there any benefit to running two side mounted intercoolers instead of a front mount, assuming comparable flow capabilities on an Audi 2.7 for example. I think this purely comes down to packaging considerations. I don't see any reason why there would be an advantage or disadvantage in doing one over the other. Quite often you will find that a single intercooler setup and the plumbing associated with that might end up working out a little bit lighter than two intercoolers and again a little bit less complexity in it but really I would focus on the packaging requirements for the front of the car and what makes the most sense. That's going to be more important than whether you chose to run a single or a twin intercooler.
Origin Alpha has asked, how does one calculate an intercooler size that won't adversely affect transient throttle response? OK that's probably getting a little bit beyond the scope of this particular webinar. I think if I remember correctly on Garrett and Spearco's websites, there is some more intricate information. So this is probably going to be more suited to those who are pushing the boundaries and are trying to go to extremes in terms of performance. For most guys at the street level, it's probably not going to be that beneficial to go to that trouble. For most people building moderately to lightly modified street engines, you can basically look at what others have done before you, look at the path that others have gone down and generally, there's not a lot of need to reinvent the wheel there so it just depends how extreme you're trying to go, as to whether or not you start needing to get into calculating the amount of heat you need to get rid of and the intercooler size et cetera.
James has asked, are there advantages to run water methanol in conjunction with an air to air intercooler? Thoughts on pre intercooler injector or post intercooler injector placement as long as they are before the intake air temp or MAF sensor. OK few questions in there James, some good ones in there. Certainly water methanol injection is something that you can use in conjunction with an intercooler, nothing wrong with that at all, probably a pretty common way to see it used. The water methanol injection will still basically go through that phase change inside of the combustion chamber, removing further heat from the combustion charge temperature. Probably what I'd say is that water methanol injection is a good way of getting around running on a low octane pump gas with a high boost turbocharged application.
Essentially gives us the potential to run boost pressures and/or ignition timing that really wouldn't be possible on a low octane pump fuel. So that's the cooling effect of the water methanol injection, coupled with the high octane rating of the methanol fuel as well. So moving into pre intercooler or post intercooler. Now this isn't something that I've personally tested. There are a couple of considerations and I know there is actually some benefits to running a water methanol injection pre turbocharger actually, pre compressor in terms of increasing the efficiency of the compressor.
What I would worry about a little bit personally if you are running an intercooler is the water basically dropping out of suspension and maybe pooling in the intercooler. I don't know if that's a real consideration or a real concern because I just haven't done it so I can't really speak to that with any personal experience sorry. A couple of questions here about water spray on an intercooler. One from Queens Fanatic. Yep great option there, we saw that with a lot of the JDM rally homologation models.
The Subaru STi and the Mitsubishi Evo both had factory fitted water sprays on the intercooler. Definitely effective, that's a great idea if you can incorporate that. One thing you do want to be careful with if you are going to do this, this is, definitely here in New Zealand, very much frowned upon for drag racing because you do risk ending up getting water from that water spray onto the racetrack. Obviously that's not going to help with traction. So there was a bit of a drive to get rid of people using water sprayers on intercoolers.
Same thing could be said on the racetrack or circuit racing but of course at high speed, given the relatively small amount of water that is being sprayed onto the intercooler, maybe not such a big consideration. You also need to consider how long your water tank is going to last for. Thomas has asked, what about water injectors they used in World War II supercharged bombers? Yeah so I kind of touched on water methanol injection as a replacement for an intercooler. It can be done, it has been done, it's been proven, would I do it these days? Probably not. Mafia Boys World has asked, can you rank the importance of air to air intercooler sizing for efficiency if all have decent fin cooling, length of the core versus the width of the core versus the thickness of the core.
That's actually a pretty good question there. So generally in most instance we're kind of going down, again this comes back to what I was saying, whether we need to go down the path of actually calculating the perfect intercooler for our purposes, we can go down the path instead of if we're dealing with a popular car, we can see what everyone else is doing. So first of all, probably the biggest consideration is the frontal area of the intercooler. And this is going to be limited mostly by the frontal size of the cutout in the car. Obviously there's not much point putting a massive intercooler in the front of the car where half of the intercooler is cut off and it's not in the airflow.
So that's your first consideration, getting something that's going to optimise the use of that cutout in the front bar, front bumper. From here, generally in most instances, if I'm dealing with an engine that's maybe 1800 cc, 1.8 litre or larger I would probably be looking at a three inch thick core. And what we find is that out there in the mainstream there are some pretty common core sizes. Three inch thick and the 600 by 300 which is exactly what we've got here. It's a pretty good run of the mill option for the majority of the cars that we personally deal with and build.
When you start getting into higher horsepower levels though, if you can't go bigger in the core surface area, this is where we start seeing some of the intercoolers increase in thickness and talking to the guys from PWR back at World Time Attack last year, this actually can be less effective than you think. So generally you're going to see a bigger improvement in cooling by going a larger surface area rather than a thicker core. So that being said, some of the off the shelf cores that we see for the likes of JZ Supras with 2JZs, R32, 33, 34 GTRs with the RB26 can be four, five, six inches thick. So yeah just basically maximising the intercooler use of the space available in the front of the car. Without trying to make this too long winded I just want to actually come back as well because another advantage of the water to air intercooler in a drag application that I haven't actually touched on is the aerodynamic advantage and I just got onto this because I'm talking about surface area.
Obviously running one of these intercoolers through the airflow, that's going to end up with creating some aerodynamic drag. Now obviously it's an essential in a road car or a road race car but in a drag race application where again we only really need to run the car for maybe six seconds at a time, often these engines don't run any coolant through the engine block at all, there's an advantage aerodynamically to shutting off the airflow through the engine bay and that's where the water to air intercooler comes in. Jack has asked, what are your recommendations about the inlet and outlet sizing on the intercoolers? In versus out principally, do you prefer an outlet slightly bigger than the inlet? OK this is actually a common question we get asked about and the physics dictates that essentially we can get away with a smaller outlet piping that the inlet piping because if the intercooler's done its job properly, it's increased the air density. The reality is that more often than not, this will actually be dictated more by the compressor outlet size from the turbocharger and the throttle body inlet size. So this is one of those situations where sometimes the physics doesn't quite end up transferring across to the real world and sometimes those considerations on turbo outlet and throttle body size are a more sensible way of sizing your plumbing.
What I would say is that for engines in the two litre capacity four cylinder, up to probably around about 600, maybe 700 horsepower, 2.5 inch intercooler plumbing inlet and outlet is perfectly workable. Once we're up above that 600 to 700 horsepower mark and aiming higher, I'd probably consider stepping that up into the three inch range. CMS GT4 has asked, how might you take into consideration pump flow speed on a water to air intercooler system? I've currently got a slightly modified OEM GT4 water to air system. So what we need to consider with the pump speed is that if we actually flow the water through the cores too quickly, this can actually be detrimental to flow. So basically the water doesn't have time to dissipate the heat to the ambient airflow, we may not get as much time for the charge air to basically get its heat into the coolant.
So there is a happy medium there, I can't give you specifics on this. It's going to be so dependent on the pump, the size of your lines as well as your intercooler core itself. But it's definitely something that could be worth experimenting with and just running your pump at various speeds and doing some logging to see how that's affecting your air temperatures. R18 Turbo, kind of a question I've already answered, are intercooler pipes that are larger better? No definitely bigger is not always better. We need to size those relative to the amount of airflow that we need and step these up as we end up making more power.
And again this comes down to, we're not going to needlessly add additional volume to our intercooler plumbing. Mr 32i has asked, are you guys using a PWR cooler in the RaceCraft 86? Not this is actually a AVO turbo kit that we've got fitted to the car. So it's a front mount intercooler. AVO I think from memory, it's an Australian company for those who aren't aware, I think from memory it is a Chinese sourced intercooler core. It's not quite 600 by 300, I couldn't remember, it's been years since I installed that kit so I can't quite remember the sizing of it.
I know it was quite short because again this comes down to using the cutout in the front of the Toyota 86 chassis. But despite it being Chinese, it was a good quality core with lots of internal fins and it does a pretty good job. I've answered that one already. Harris 4G63 has asked, are there any gains to be had when running methanol fuel with its latent heat properties to cool cylinder temps by adding in air or air to water intercooler, kind of already answered that. Comes down to really personal preference from what I see in terms of the tuner and the engine builder.
I've seen cars go just about equally as fast with both so obviously it's not necessarily a limitation on the power. James has asked, any rule of thumb for downsizing an intercooler for a rear mount turbo versus a front mount? Rear mount turbos, something that I have never dealt with in my career. Definitely some considerations in there. It's probably something I'd need to put a little bit more thought into rather than trying to answer a question live here in our webinar. Obviously if you're going to end up with a rear mount turbo setup versus a front mounted intercooler, you're going to be putting a huge volume of plumbing into the system there.
But yeah there's some issues with mounting of the rear mount turbo kits anyway so that could be a situation where a water to air intercooler might make a lot more sense. R18 turbo has asked, if you fabricate a large plenum for the intake air to dump into your intake manifold, does the temperature drop, does the pressure equalise? The volume of your plenum is not going to really impact at all on your air temperature. Really what we need to do is get rid of the temperature using the intercooler before the air ever reaches there. Michael has asked, what do you think about C02 spray in the intercooler? Actually that was it, it was a CO2 spray, I talked about this earlier in terms of the nitrous spray. Now nitrous spray onto your intercooler will work, it's very effective but as I mentioned, very expensive and I think you're right, it was actually a CO2 spray that I was trying to think off.
Right guys I am sorry we are just out of time so I'm going to have to wrap it up here, I've got one more question that I will answer. I know there's a few whose questions I haven't been able to get through to but we are just out of time. So our last question, a lot of intercooler kits come with custom piping as well as couplings, how do you determine the proper ratio between piping and throttle opening for most street strip cars? This can be a little bit tricky and really some of this comes down to a bit of experience and again kind of looking at what everyone else has done if you're going down a well trodded path. So in most instances I try and keep a relatively good match between our intercooler plumbing and the throttle body size. It's not always going to be the case though.
For example if you're running a big four inch, 100 mm throttle body, there'd be very few applications on the street where you would truely need a four inch intercooler plumbing so then again we get to that situation where four inch intercooler plumbing is just adding a lot of unnecessary volume into the intercooler system. So what I'd probably do there is run, again depending on our power aims, if you're running a four inch throttle body, chances are you're probably going to be looking at making some reasonable power, might make sense there on that application to run something in the range of three inch intercooler plumbing and we can just step that up with a coupler at the throttle body. Alright guys, again sorry to those whose questions I haven't been able to get through to but hopefully everyone's learned a little bit more about intercooler options, some of the considerations, probably one of the big takeaways I really want to drum into your here is, because it's becoming more common, the difference between the intercoolers' internal flow. Whether it's a big open flow with no internal fins or one that has a good high density of internal fins. The important part there is those big open internal flow paths do almost nothing to get heat out of the air so you're going to end up with a very sub par performance.
As usual, if you've got any questions that come up after today's webinar has aired, please ask those in the forum and I'll be happy to answer them there. Thanks for joining us and we'll see you all again next time.