198 | Selecting The Right Turbo
Choosing the right turbo for your particular engine and application can be the difference between a powerful and responsive engine and a laggy dog that just doesn’t deliver. In this webinar we’ll look at the considerations that go into choosing a turbo and see how we can use online tools such as Borg Warner’s Match-Bot to help select the right turbo the first time.
- Hey guys it's Andre from High Performance Academy. Welcome along to another member's webinar. Now today we're gonna be talking about quite a tricky topic. We're going to be talking about sizing the turbocharger or a correct turbocharger for your engine. And this is a difficult topic because there are simply so many options out there in the turbo aftermarket world these days, that it can be quite daunting to decide on exactly what turbo is going to fit your aims.
Particularly when we're also talking about a turbocharger being what is quite an expensive addition to your engine, you don't wanna be going wasting money on a turbocharger that once you get it on the engine, doesn't prove to do what you want it to. As usual with this webinar, we will be having questions and answers at the end. There's a lot to cover here so if there's anything that I talk about that you'd like me to delve into in more detail, please ask those questions in the comments and the guys will transfer those through to me. Now part of the reason that turbo sizing is quite tricky is that there are so many variables that can affect the way a turbocharger is going to perform on any given engine. So I'd like to say here that turbo sizing is definitely a science but I sort of would also say it's a slight combination between a science and an art.
So we'll find out some techniques though as we go through this that will take some of the confusion away and give you the best possible chance of getting the correct outcome for your application the very first time around. Now if you get it wrong, obviously there's two downsides here. The first is if you go with a turbocharger that is too large for your application, you're likely to get into a situation where you've got absolutely no low RPM performance. It takes a certain amount of exhaust gas energy to actually get the turbocharger moving and producing air flow which results in our boost pressure. And if we don't have enough exhaust gas energy to drive the turbo at low RPM, we're going to end up with no low RPM boost.
So this is a particularly important consideration for those of you who are sizing a turbocharger for a street application. Also those of you who are sizing a turbocharger for circuit racing. Here we really need to trade off that often outright power is not the most important thing, and particularly for a street application, it's actually going to be pretty frustrating and often quite slow driving around in a car that doesn't produce any real performance below about 5500 or 6000 RPM. Now fortunately as well we have seen some massive advances in turbo technology over the last decade and we're really fortunate these days to have access to some really advanced turbochargers from the likes of BorgWarner we've got an EFR8474 sitting in front of me. Also Garrett are coming a long way with their GTX turbochargers and their new G series turbochargers which we're going to be talking about in a little bit more detail as well.
We've seen advances in the aerodynamics in the wheel designs, some advances in the materials as well that have all added up to give us turbocharger performance that we simply couldn't have dreamed of, probably no more than about five to eight years ago. Alright I was talking about the downsides of getting the turbo wrong, of course we've just talked there about what happens if your turbocharger is too big. The flipside of that coin though of course is if you've got a turbocharger that's too small, you're gonna get great punch off the line, it's gonna build boost exceptionally well at low RPM. But you're also going to end up with that turbocharger essentially choking air flow through the engine at high RPM. It's not gonna be able to flow the sort of air that we're going to need in order to make really high power levels.
So it really is a case of deciding on what compromise you want to make and where abouts in the power band you're expecting to make your power. Now I'm going to start here by talking about a term that I think when it comes to turbo performance in general, is largely misunderstood, and that is boost pressure. I know that a lot of enthusiasts really think that boost pressure is one of the key metrics when it comes to turbo performance. And in my opinion it is largely irrelevant. Now that might sound strange, obviously we need to know how much boost our engine is running.
But there is a lot more to it than boost pressure if we want to know how much power our engine is likely to make so that's why I say it's largely irrelevant. So what I'll use for an example here is if we were running 15 psi of boost on let's say a two litre Mitsubishi 4G63 engine using a Garrett GT3076 turbocharger. And then we took that 3076, we threw it in the bin and we fitted a Garrett GT42 just for a quick example there. The GT42 a much bigger turbocharger, much bigger compressor and exhaust housing. Particularly there the exhaust side of the turbocharger is going to pose a lot less restriction to air flow through the engine.
So what I'm getting at here hopefully most of you watching could probably understand that 15 psi of boost pressure on the 37S6 is going to give us a vastly different amount of power from exactly the same engine compared to what we would get if we swapped to that Garrett GT4202. So the way I like to try and explain boost pressure in a way that's simple to understand is the boost pressure is really a way of thinking about the amount of restriction that the engine itself poses to air flow. So in other words all things being equal, as we open the air flow through the engine up, we allow the engine to breathe more easily. For the same boost pressure we're actually going to be moving more air. So another way of looking at that or another sort of way we can break that down is that if we have exactly the same turbocharger on our stock engine, and then we take our engine apart and we do all of the sort of work that we do to our engines when we're modifying them, I'm talking here about freer flowing intake systems, I'm talking about larger inlet manifolds perhaps that flow better.
Maybe we're porting the cylinder head and adding a set of cams, a free flowing exhaust. All of that work allows the engine to breathe more easily. In other words it increases the volumetric efficiency of the engine. So now when we fit the exact same turbo back on that engine and we run the same amount of boost pressure, we're going to end up with our engine making more power and hopefully that's something everyone can relate to. So while yes we do need to know and have an idea of how much boost pressure we're running or what boost pressure we want to run, you cannot make a direct correlation between boost pressure and power.
There's a lot more in it than that. It's also really important there to understand that relationship when we're looking at trying to make a lot of power from a turbocharged engine in a small capacity application. So this is sort of my background was import drag racing where we were using two litre four cylinder engines, we're trying to make 1000, 1200, 1400 horsepower out of these engines. Now in order to move the amount of air through such a small capacity engine, the way we need to do this is by running very very high boost pressures. Conversely, and this is really to overcome the restriction that the engine poses to that air flow, conversely if we wanted to make that same amount of power out of let's say a six litre GM LS2 V8, we've got a lot more capacity there, the engine can physically flow more air so we're not gonna need anything like that sort of boost pressure in order to make the same power that we're trying to get out of our small capacity engine.
Alright the next topic that I wanna talk about, sort of another breaking down a few myths and misconceptions here, we're going to talk about the term lag. And this is so often misused. So really there are two terms that are unforunately out there in the wider industry tend to be mixed up and used incorrectly. I use the term lag and I use the term boost threshold and they are not the same. So boost threshold refers to where abouts in the engine's rev range we can achieve our full boost.
So let's say for example we're trying to make 15 psi of boost, we may, depending on the size of our engine and the size of our turbocharger, we may not be able to get to that boost set point until, let's say perhaps 3000 RPM. So that is our boost threshold, what I'm actually going to do is just give you a quick visual drawing of this, I'll apologise for my crappy sketching skills, but let's head across to my laptop screen. So what we'll do is we'll draw a vertical line here, so this is our boost. Let's just put a B on there. And then on the horizontal axis here we've got our RPM.
OK so a typical boost curve might look something perhaps like this. And this is the point here where we've reached full boost, this is our boost threshold and let's say as I've said, that might be 3000 RPM. OK so that's one aspect, and this is the term that most people confuse or use incorrectly for lag. Once we're above that boost threshold though, if we back off the throttle. So let's say for example now we're at 4500 RPM, we're at full throttle, we've achieved full boost, we back off the throttle, we completely close the throttle, maybe we're coming up to a corner, we're still at 4500 RPM so we're still above that minimum boost threshold.
But when we put our foot back on the throttle, we go straight back to full throttle, the turbo can't instantly jump back to that 15 psi. Granted they've got a lot better over the last decade but they still can't instantly get back to that 15 psi. So if we were to look at what happens when we go back to full throttle, let's just look at this time, let's try again. Told you I wasn't very good at drawing. Right we'll still use boost there on our vertical axis and this time we're going to have time on our horizontal axis.
So we're above our boost threshold and what we find is that when we jump back on the throttle we end up with our boost doing something like this. So there might be somewhere in the region of maybe a 10th of a second or thereabouts in time lag before the turbo reaches full boost again. So this is the term that we're confusing with lag. So just important to understand the differentiation between boost threshold and lag. So the boost threshold itself, the reason we have that is because we need a certain amount of compressor or turbine wheel speed in order to achieve the air flow that we need in order to reach our boost target.
So this really comes down to providing the turbocharger with enough energy from our exhaust gas. And of course we don't have much exhaust flow at very low RPM. As the engine RPM increases, our air flow through the engine increases, we start supplying more an more exhaust gas energy to the turbocharger which drives it harder and harder, hence that's why we can make our boost pressure. On the other hand, our lag really comes down to the fact that the rotating assembly inside our turbocharger, the compressor wheel and more importantly the exhaust wheel, they are relatively heavy. And they have a certain amount of inertia to them so again we can't instantly jump back to getting our full boost set point.
And as I've said, there's been some pretty big advances in the turbo technology that have really helped reduce in particular, or actually both, the boost threshold as well as the lag which we're going to talk about shortly. Alright so let's get into that actually right now which is what affects the turbocharger's performance? So obviously the size of the wheels themselves, to flow a specific amount of air we're going to need a certain size wheel, obviously as we want to move more and more air we tend to see the compressor wheel get bigger and bigger, and we also as a result need to flow more exhaust gas out the other side of the engine so our exhaust wheels get bigger and bigger. It's hard to draw a strict correlation between the size of the compressor and turbine wheels with how much power the turbocharger is capable of supporting. Particularly these days as we've seen advances in aerodynamics and materials used in turbochargers. The size of the turbochargers and the amount of power they're able to support, just would not have been believed just a few short years ago.
So that first topic that I wanna talk about here in terms of the aspects that affect our turbo performance is the aerodynamics. And this is where we've seen huge advances both from Garrett, from BorgWarner, as well as the vast majority of other name brand players out there in the market, Precision for example, and I'm not trying to pick just a couple of brands here, it's just the reason I've mentioned Garrett and BorgWarner is we're gonna have a look at their online calculators really shortly. So this has come in a number of ways, we've seen obviously a lot of advances in the ability to perform computational fluid dynamics. This is seen in general aerodynamics, it's being applied to turbocharger technology as well. And the reason this is important to the turbo manufacturers is it means that a lot of their development can be done without ever having to make a physical product like this, so they can make design changes to the compressor wheel, and run it through tests in their CFD software and they're going to have a really good idea if the direction they're moving in is an advantage or a disadvantage.
So instead of trying 50 different compressor wheels for example, manufacturing those and then physically testing them in a real life environment, what they can do instead is really narrow down to maybe five designs that they think are going to work well based on the CFD testing, produce those and it just improves or speeds up the prototyping process. So that's important to understand. Now the other topic I'll talk about here is a billet compressor wheel versus cast. And again I think this has become a bit of a hot topic out there in the turbo industry. And it is something that a lot of turbo manufacturers are using as a sales point.
Billet wheels look great, they're nice and shiny but it's important to understand why turbo manufacturers are using billet wheels, and also important to understand that just because your turbocharger has a billet wheel, that doesn't necessarily mean that it's going to provide better performance. Now let me kind of get back to why that is the case. So first of all, one of the key reasons why billet wheels have become so prominent these days is that it is much easier to produce short runs of turbochargers using CNC machining of a piece of billet rather than actually casting the wheels. It's a much faster process. That being said, it doesn't really lend itself well to large scale production volumes so in the OE world, we're probably unlikely to see billet wheels becoming mainstream, the sort of production numbers that are required at the OE production vehicle level is simply so great that cast wheel just simply make a lot more sense.
But for performance turbocharger applications, and it's also worth mentioning here for us in the performance world, it's easy to forget that, or think that the performance world is all powerful and all encompassing. But the reality is that the performance brands from the likes of Garrett, the likes of BorgWarner et cetera, actually are only a tiny percentage of their overall turbo production. The number of turbos they're producing for a performance application might be only a few percent compared to their overall OE production. So that's one thing to consider there. The importance of their performance turbocharger line compared to their OE line.
And those numbers. Anything they can do to speed up the production and the prototyping is valuable and that's where those CNC billet wheels come in. It allows them to test multiple designs and validate them in real world conditions much faster than if they were to produce cast wheels. Now there are some genuine advantages to billet wheels as well. They are generally able to be stronger, produced to be stronger than a cast wheel and this is really important for those guys pushing turbochargers to the limits, particularly in drag applications where we're seeing people running 100 plus psi of boost pressure and compressor wheel speeds that really are at the absolute limit of the reliability.
The billet wheel is simply stronger at that kind of level. The other reason that we can see a small improvement in performance from a billet wheel compared to a cast wheel is because of that strength it's possible to machine the hub where the compressor wheel bolts onto the shaft, a little bit narrower, a little bit thinner, so we're actually flowing a little bit more air or have the potential to flow a little bit more air for the same compressor wheel diameters. Now what I've kind of overlooked here which I should have said right at the start is basically the billet wheel, if we take a billet wheel, we can manufacture a cast wheel for all intents and purposes with exactly the same profile, the same aerodynamics. Not withstanding what I've just mentioned about the hub. And all things being equal, just making the compressor wheel out of a billet material and CNC machining it does not in and of itself mean that that wheel is going to make more power or flow more air.
It's all of those other reasons that I've mentioned there. So don't just get sucked in there and think that billet wheels are an absolute must have, just understand where they sit in the big scheme of things and why manufacturers are now turning to them. Now the other advances we've seen here which have really improved our turbocharger performance is in the materials being used particularly in the turbine wheel. Now I said that one of the factors that affects both our boost threshold as well as our lag is the mass of the turbocharger's rotating assembly. We need to overcome the inertia of that rotating assembly in order to get it up to speed and produce boost pressure.
So anything we can do to reduce the mass of the components is going to help there. We saw some drives towards this back in probably the earlier days of turbocharging now. Nissan were one of the manufacturers, one of the OE manufacturers that turned to ceramic turbine wheels. For our purposes in the aftermarket that was an ill fated move because anyone who has tuned Nissan vehicles running the ceramic turbos will know that they are prone to falling off if you run too much boost. This is because the ceramic material was essentially bonded to the steel shaft of the turbocharger.
Also not very forgiving if something goes through it. You're more likely to end up with the blades on the turbine wheel breaking. These days we've seen advances and some of the common materials up until recently were the likes of inconel, very well suited to high temperature operation. These days the two materials that I'm gonna talk about is in the BorgWarner range, the EFR range. They've moved to what they've referred to as Gamma-Ti.
In the new Garrett g series they've moved to their own proprietary material call Mar-M. I'm not a metallurgist, I'm not gonna jump in and start trying to explain to you what those materials are actually made of but in laymans terms, what we need to understand is that they are a lighter material. So the turbocharger can be manufactured out of this material and be lighter, the rotating assembly is lighter, giving us all those advantages we have talked about. Some of these materials, another advantage with them is that they can support higher operating temperatures. For example with Garrett's G series turbos using the Mar-M material, these are now rated to continuous use of 1050 degrees centigrade.
So that's getting up there but of course as we see, more and more people push turbos harder, we do need materials that will support that sort of operating temperature. The last aspect, I'll just talk about here is twin scroll versus single scroll turbine housings. I'm hoping that anyone who's done any kind of research into turbochargers will probably have already heard of those terms and maybe have a rough understanding of how that works. But this particular 8474 here does use a split pulse exhaust housing. So basically it has twin scrolls that go to the turbine wheel and what we want to do when we're manufacturing a turbo manifold for a split pulse exhaust housing, is we wanna take advantage of that with the firing order of our engine.
And it's about trying to deliver the pulses, the exhaust gas pulses to the turbine wheel in a way where we can get most advantage from those acting on the turbine wheel. So in general, it's actually also I should say quite difficult to get a back to back comparison where the only thing that has been changed is an open scroll to a split scroll housing. But generally what you're going to find is that if you do that, you're going to end up with better low RPM boost response or alternatively what you can do is jump up to a larger exhaust housing, a freer flowing exhaust housing with a larger AR. That's still gonna give you the same low end boost response, but alternatively what it's going to do is give you less turbine inlet pressure. Don't worry about these terms, I'm gonna talk about them in detail really shortly.
So you're going to end up with an engine that can produce more power without sacrificing bottom end performance. Alright so with some of those basics out of the way, remember if there are any questions about anything that I'm talking about, just ask them in the comments and I'll try my best to answer them. We had to kind of get that background bit out of the way before we can jump into the actual topic here which is turbo sizing. And what we wanna talk about for a start is the options available to us when it comes to choosing a turbo. One of the options which is probably easiest because you're essentially handing over responsibility to someone else, is to rely on a performance workshop that is familiar with your car.
Now that's not really gonna be the main focus here of our webinar. Clearly that's not exactly scientific. But it isn't a bad option if you live in a part of the world where you've got some great specialists who know your particular model of car inside and out. And what I'll do there is give just a couple of examples there. The likes of AMS Performance in the US, they are very well versed with the R35 GTR platform, they've done a lot of development, and they know what sort of turbochargers will provide what sort of power range and when you're talking to a shop at that kind of level, you can basically state to them your power range and what you want to do with the vehicle.
They're going to be able to tell you very very accurately what turbo setup is going to suit your particular vehicle. They've done it all before, they've got the data, they're probably going to be able to even give you dyno plots to show you exactly what you expect to get. Now I've used AMS Performance as an example there. Obviously there are workshops around the world that specialise in all sorts of different vehicles. So if you're dealing with something popular, maybe the Mitsubishi Evo range, maybe the Subaru WRX STi range.
All of these sorts of turbo set ups have been tested and tried to death and workshops that specialise in those vehicles will have a really good database of what does what and will be able to help guide you in the right direction. Now from there you can also choose to do your own research on the internet. Now the internet is a scary place and this can end up wasting hours if not days, it can also send you on a wild goose chase. So you do need to temper this a little bit with what you're expecting to achieve. You need to understand that you're going to see a lot of conflicting information.
So if you wanna go down this path, it is really important to be able to sense fact from fiction and what you're looking for here is a lot of results that back up the same numbers so that you can be confident. Now this is only gonna work if you are dealing with a fairly common platform. So I've talked there about R35 GTR, I've talked about Mitsubishi Evo and also Subaru. It gets a little harder when you are dealing with something a little bit out of left field that isn't popular for modification. So we'll deal with how to look at that in the next section.
But for a couple of examples there of how this can work, Let's just jump across to my laptop screen for a moment. So this is the Full Race website and this isn't a sales pitch for Full Race. We don't make a cent if anyone buys a turbocharger from Full Race so I just wanna be really clear about that. But this is for the BorgWarner EFR 8374. The reason I've gone to this particular website is because they do a reasonably good job of trying to give you a bit of information around this turbocharger.
So the first thing, if we come down here a little bit, you're going to see under description, let's try that for a start, you're going to see exactly what the turbocharger's capable of doing. So basically it says that it is going to be able to flow somewhere in the region of 500 to 800 horsepower in a single application or up to 1300 horsepower twin turbo. OK great that's some information that's helpful but where it does get useful is if we jump across to their results tab. We'll go through these videos which we're not that interested in and we'll get down to, they have a range of dyno plots for a variety of different vehicles running the 8374. Now it's useful to a point, particularly if you do happen to have one of these vehicles that is in this list then great you can kind of see exaclty what you can expect from that particular turbo and that particular application.
Problems with that are that you don't necessarily know every single modification that has been made to that vehicle to help support the turbocharger. And then of course as we've just seen, there's a variety of different dyno plots available and we all probably hopefully know by this point that not all dynos are created equal so that does add a little bit of confusion. Now the other option again with a common platform is we can also have a look at enthusiast forums. So again on my laptop screen here, let's say we wanted to see what the performance of a Precision 6266 turbocharger's going to be on a stock block Evo 8. Basically you can put that search criteria into a popular enthusiast forum.
In this case I'm on the Evo M forum. And you're going to be able to often get exact results as to what other people have achieved on that so it's not a bad way of going to get a bit of a feel for what sort of turbocharger options are out there, what sort of turbochargers people are using to get the power levels that you're aiming for, and then if you've got a particular turbocharger in mind, it's a good idea to get a feel for where you're gonna see full boost, how usable the bottom end performance is going to be, those sorts of things. Alright so now what we're going to do is get into the more advanced side of turbo sizing and this is where we can start using specific turbo sizing tools. The two that I'm going to cover here, there's one called the Boost Advisor which is Garrett's one. This is relatively simplistic.
But it is going to be helpful for getting you a reasonable guide as to which turbos in the Garrett line up might suit your application. And then we'll have a look at BorgWarner's Match-Bot which is much more sophisticated and requires a lot more input from the user. Before we do that though it is important here to understand some of the basics around reading a compressor map. We do need to know what we're actually looking at on a compressor map and what all the numbers mean. So let's just have a quick look at a compressor map, we'll jump across to my laptop screen again for a moment.
And this is what you're likely to see from most of the manufacturers that produce compressor maps and we've got two axes here. On our vertical axis is our pressure ratio. So this is simply the pressure coming out of the turbocharger so the compressor outlet pressure, divided by your compressor inlet pressure. So basically it's the pressure working across the turbocharger's compressor wheel. So most instances we're going to assume that the compressor inlet pressure is barometric air pressure.
The reality is it's often going to be a little bit worse than this because we can see a restriction before the compressor inlet based on the restriction of our air filter, maybe the inlet plumbing up to the turbocharger. So we may end up being a little bit lower than that. But to give you some really rough numbers here, if we were running 200 kPa of boost pressure, and we had 100 kPa of atmospheric pressure, then we would be running at a pressure ratio of 2.0 so we're going to be running across this area in our compressor map here. The horizontal axis that we've got here is our corrected air flow in pounds per minute, so this just gives us some kind of indication of how much air the turbocharger is able to move. It's a really key consideration when we are choosing a compressor capable of supporting a certain power level.
If we can't flow enough air then we're not gonna be able to make that power, it's that simple. Then inside of the compressor map itself we have all of our efficiency islands here. There are a couple of points that are worth mentioning on our compressor map. First of all the line on the left hand side of our compressor map is quite an important one. This is called the surge line or surge limit.
And when we are plotting points on this compressor map, which we're gonna get into really shortly, it's important to make sure that we aren't operating on the left hand side of this surge line. We don't wanna be out here. If we run the compressor into surge, it becomes very violent, it's going to be quite damaging to the turbocharger components itself, and it's not gonna be a pleasant experience driving a car that is surging. Likewise on the right hand side here we've got our choke limit or choke line, and basically this is the point where the efficiency of the turbocharger just drops off a cliff and instead of moving air, it's just pumping more and more heat into the compressor outlet air. So Ideally what we wanna be doing understandably is running somewhere in the middle of this compressor map.
And the islands inside this compressor map show how efficient the compressor is at this point. So for example the peak island here, we can see that the compressor is 76% efficient. Now in layman's terms what that means is that when we compress air, physics dictates that we will add heat to the air. We can't get around that, we're always going to be heating up the air which is why we need an intercooler. However the worse the efficiency of the compressor wheel is, the more heat it's going to be adding into that air.
So the intercooler's going to have to work extra hard. And also the more energy the turbocharger's going to require or the compressor's going to require in order to move that amount of air. The last topic or last point on the compressor map as well is we've got these lines running down like this and these are the turbine speed lines. You can actually see the numbers on the right hand side for the turbo speed. So these show us how fast the turbocharger is operating.
These days as well as we'll talk about at the end of the lesson, we have the ability to actually validate some of these numbers ourselves. Important just to have a basic understanding of our compressor map. There is also a rough rule of thumb here that when we are looking at air flow numbers, we need approximately 9.5 to 10.5 pounds of air flow per minute for every 100 horsepower we want to make. So for example if we just jump back across here to our BorgWarner 8374 page, I'll just get back to our description here. We can see that the air flow capability, the max air flow here on that is 79 pounds per minute.
So in rough terms this means that the turbocharger is going to be capable of flowing somewhere in the region of about 800 or 790 horsepower, let's call it 800 for round numbers. So that's one of the key numbers that we do need to keep in mind. It isn't 100% reliable though, we can't guarantee that just because we have a turbocharger capable of flowing 79 pounds of air per minute, that that's what we're going to make, 800 horsepower. The turbo flow, to get that flow we need to be operating in the correct pressure ratio. And there's also other aspects to do with our engine design that can affect the ability to make the sort of power the turbo's capable of.
So for example what I mean here is if we're operating on a low grade of pump gas, a low octane pump gas, then we're almost certainly going to be what I will refer to as knock limited. And this is the point where we start increasing the boost pressure and advancing the ignition timing, we get to the onset of detonation. Clearly we can't operate our engine with sustained knock or detonation occurring. So we need to retard the timing or reduce the boost pressure in order to prevent that. So this can artificially limit the sort of power that we can get out of even a 800 horsepower rated turbocharger.
The other aspect there as well is it also depends on your engine's ability to actually move air through it. So if you've got a very restrictive engine that maybe has a very small camshaft, maybe a very small exhaust system or a restrictive intake, that is also going to be a limitation. Alright so what we'll do here is we'll jump into a couple of demonstrations, and I'm gonna start with the easiest one so let's head across to my laptop screen. You can find this at your leisure on the Garrett Advancing Motion website. This is their boost adviser.
So we'll go through a quick example here, let's click on begin. And what we're going to do here is put in some round numbers for our Nissan SR20 VE and we'll see what Garrett's website comes up with for this. So let's say for example here we are targeting 700 horsepower. So we enter that, click next and we're going to go down to our next question which is what is our engine capacity? So in this case we have a two litre four cylinder engine. Click on next.
We're only going to install one turbocharger on this engine. Nothing's particularly difficult so far. Here we need to tell them what fuel we're going to run on, in this case E85. So that's gonna remove some of those problems around the restriction, the knock limitation I should say, of the engine. What is our intercooler type? We're running an air to air intercooler.
And then we also need to tell the boost adviser how many vavles are in the engine so this is around the volumetric efficiency of the engine. Now we're going to look at our engine mid range RPM. So let's just for example here enter 4000 and we'll try make peak power here at 8000 RPM, we'll click next. And we'll say that we are at sea level, we're pretty close here in Queenstown. Let's take our ambient temperature here as 20 degrees C, and we'll click next.
This particular part, not a lot of use for me but we'll click on show recommendations and we'll see what Garrett have come up with. So first of all we've got some suggestions around the power the engine will make as well as the boost pressure and pressure ratio we're going to need to be operating at as well as our intake manifold temperature, corrected air flow, et cetera. And we can see here our max power RPM we should be able to see around 700 horsepower, with about 34 psi which equates to a pressure ratio of about 3.37. Our intake manifold pressure would be around 102 degrees farenheit. I can't convert that to C in my head but that doesn't really matter.
And we're going to be using 56.74 pounds per minute of air flow. Alright so let's look at the turbochargers that are likely to be able to do that. And we've got here a GTX 3076 which interestingly is the turbocharger that we're currently running. Or alternatively we could step up to a 3576. Alright that's helpful to a point, it's given us two turbocharger options that should suit those aims.
Now here the system from Garrett, the Boost Adviser is quite simplistic. That's OK, they've made the choice to do this because this is a complex topic and what we're going to have to do is make a trade off here between how many inputs we need to provide the Boost Adviser and how accurate and how complete our results set are going to be. Essentially if we ask more and more information from the user, it's going to be hard for a lot of mainstream users to be able to provide this information and get the results. So this isn't a bad compromise here. Both of those turbochargers are probably going to do a more than adequate job of making that sort of power level.
So you're in the ballpark, you know what will work, problem is you're not going to have an exact idea of what that particular turbocharger may do on your engine. Alright so what we'll do now is we'll jump in and we're going to have a look at BorgWarner's MatchBot. So this is a lot more complex, it is going to require a lot more information from us. And there's a lot more room for error. So this is gonna suit the more tech heads among our followers out there.
There are also, I'll mention here, I'm gonna go through a simplistic approach to this, I'm not gonna cover everything in detail or we'd be here for another hour. If you are interested in learning a little bit more about MatchBot, BorgWarner have produced their own YouTube series of videos on how to use the MatchBot. It's really great, it's really simple to understand and that should get you up to speed with the system pretty easily. Alright so what we're going to do here, this is MatchBot, you can find it by searching MatchBot and BorgWarner, pretty easy. To start with we've got some information at the top here that we need to enter.
So in particular our turbo configuration we're going with a single turbo here. What we're actually going to be doing is looking at sizing a turbocharger for a 2.6 litre Nissan R32 GTR RB26 engine. So we've got our engine capacity in litres there at 2.6 litres. It's asking for our ambient temperature which I've just put in there at 70 degrees fahrenheit. And again we're just assuming here that our altitude is zero, we're at sea level, so we're running under standard atmospheric conditions, 14.7 psi.
And our fuel for this particular application is going to be pump gas. Alright so now we need to enter some more information here. We've got six points that are going to be plotted on our compressor and our turbine maps. And we can, to start with, choose the engine RPM for these set points. I've actually left this at the default values because we're looking here at something that's going to be relatively responsive and provide good boost response at low RPM.
So I've left my first point there at 2000. So we obviously span that out to 7000 RPM. The next line down is our volumetric efficiency. Now this is one of the problems with these sorts of calculators is there are some assumptions that need to be made here. Most people, including myself, are not going to know accurately what the volumetric efficiency of your engine is.
So we are gonna have to take a bit of a guess here. If you click on the little question mark here, there are some ideas or sensible starting points to use. What we've done here is we've assumed that our modified RB26 is gonna be pretty efficient and we're using numbers about 100% 105% from sort of 4000 RPM and above. VE a little bit lower, down at low RPM. Then we're looking at our boost pressure here so we've said that at 2000 RPM it'd be great if we could get five psi.
We're expecting that it's gonna ramp up and we're gonna have about 15 psi by 3000 and then we're going to hold our boost at a maximum of 18 psi. So this should be something that's achievable in an application, it's gonna give us a nice power band. It's gonna give us a decent amount of power and it's also gonna be able to be nice and responsive. Next up we have our intercooler efficiency. Again something we're really gonna be having to take a bit of a guess at here.
So we're just using some default values from BorgWarner. We're 96% efficient at low RPM, this is because the air flow through the intercooler is quite slow so it's easier for the intercooler to remove heat from the air. That drops down a little bit, we're at 90% efficiency at 7000 RPM. In some instances it may be lower than that, so obviously that's gonna depend on your intercooler. Next we're also going to see a pressure drop across the intercooler which is our next line here.
Again I've just left this at the default values and we can see at 7000 RPM we've got 0.6 psi pressure drop. That would probably be for a reasonably efficient intercooler. If you're running a stock intercooler and you're pushing it pretty hard, it wouldn't be hard to get one psi or more pressure drop across the intercooler. Likewise the next line down we've got our air filter restriction, I kind of touched on that earlier, something that's often overlooked, and again without hard data I'm just leaving this at the default values. Next we've got our back pressure in the exhaust system.
So this is the back pressure on the outlet of the turbine housing, or sorry the outlet of the turbocharger, so where the exhaust connects up to the turbo itself. And there's always gonna be some restriction here. Again unless you've actually measured this you're going to be taking a bit of a guess. The values here are quite low, two psi at 7000 RPM. It's actually not very hard to exceed that so this would be quite a free flowing exhaust system.
And if you've got a restrictive factory exhaust system, I've seen in excess of 10 psi. So just consider that because it's something that is often overlooked. It's gonna make a lot of difference to how your engine runs. Next we've got our compressor efficiency and to start with what we're going to do is leave these numbers here at the default values, we can come back to them and manipulate them a little bit later on once we actually know where we're operating in our compressor map and have real values. Likewise we've got our turbine efficiency below that, we're gonna leave that alone, and our exhaust gas inlet temperature.
So these wanna be some relatively sensible numbers and we're running 1650 fahrenheit which I think off the top of my head is about 900 degrees C at high RPM. Probably pretty realistic for our pump gas application at that sort of boost level. We've also got our brake specific fuel consumption and our air fuel ratio. So you will notice that at this point, I actually haven't made a lot of changes here so while yes there's a lot of data that needs to be put in, and the more data we've got and the more accurate it is, clearly the better job MatchBot is going to be able to do. But even with those default values, that's gonna be a pretty good starting point for a moderately well modified hot street or maybe race engine.
OK so what we're going to do now is come down and we'll click that closed. The first thing we're gonna have a look at here is our matching of our operating points to our compressor map. So this is basically a situation where we can choose a range of compressor maps, and see what actually suits the points that we've plotted. So we can see those red dots there, those are our six plotted points. And to start with, we've got this plotted against a 6758 EFR turbocharger.
Now you can see that we are well within the surge line here, everything is within the surge line. However you can see that particularly our operating point six, we're past the choke line there. We're not going to be able to get a good result if we are operating on that 6758 compressor wheel. So what we can do is simply choose from our drop down menu here, and we can try fitting a different compressor wheel and see how that works. So we'll try the 7064 and we can see that pur operating points five and six are still right on the extreme or off the extreme of that compressor map.
So not what we want. Let's just jump up to the 7163. This actually looks like not a bad spread. We're still getting pretty close, we're gonna be pushing that turbo really really hard at 18 psi at 7000 RPM but we haven't got a bad spread across that. Particularly the points three, four and five.
We're operating through a reasonably efficient area of that map. We are still staying clear of that surge line. So this probably isn't going to be a bad option for our compressor wheel there. Alright so now there's a little bit more information we need to consider here which is our turbine expansion ratio here. And this helps us size our turbine housing and turbine wheel as well as getting a pretty good idea of what sort of boost response is realistic.
So in other words, how much boost can we get at what sort of RPM. So we'll click here on our turbine map. All of these you can just click to either expand them or shrink them down. And I've already gone through and I've done this just to speed up the process a little bit. But basically again looks pretty confusing, don't worry, it really isn't.
What we've got on the right hand side here is the turbine wheel outside diameter as well as the AR of the exhaust housing. And what we wanna do here is basically manipulate our turbine expansion ratio numbers here in order to make sure that all of these little red dots are located on one single line. So what I've done here, I'll try and actually just zoom this in a little bit so you can get a better idea of this. Hopefully you can see that all of these dots are on that one line and if we come up through that line here, we can see that this is for our 63 millimetre 0.5 AR exhaust housing combo. So that's the exhaust housing that we'd be using with our 71 millimetres compressor wheel.
So if we move back up here, I'll just shrink that back down a touch. You can see that this gives us our percentage of wastegating. So in other words, how much of our exhaust flow is being sent out through our wastegate. So we can see that we were asking for five psi here at 2000 RPM, and we're only just barely have that wastegate cracked open, it's running at around about 16.4%. So what I'll do, and I'll just show you what happens here.
If we are asking for a boost pressure that simply isn't achievable, we're going to see that this says N/A, it's basically saying that the turbine match is not possible in order to provide enough energy to the turbocharger, in order to achieve our five psi of boost pressure. So what we need to do is adjust our number up until we've got some positive values there, we are actually getting enough exhaust flow. So this can also be used to help with our sizing of our wsategate. We kind of know how much air flow is gonna be going out through our wastegate. Alright so with that information there, we kind of know there that the 7163 is probably gonna be a reasonable match for that particular application.
And it's going to be probably right on the limit at high RPM. And we know that we can get away with the 0.84, was it 0.84? Let me just have a quick look, 0.85 AR exhaust housing. And we can have a look and sort of get some idea on what that is going to give us. So we click on our calculated outputs. Again there's a lot of information in here.
Doesn't need to be that scary, some of the key parameters that we wanna look at here is we've got our calculated pressure ratio, we have got our corrected air flow, in this case in pounds per minute, 51.19 pounds per minute. And where we come down to some of the useful values here, we can see that this turbocharger combination should be capable of producing around about 490 horsepower flywheel. But there are a couple of other things we need to take into account here. Now the problem with running a small turbocharger and really pushing it hard is that at high RPM in particular we find that the turbine side of the turbocharger starts becoming a restriction. It kind of starts choking down our engine, the engine can't get rid of that exhaust gas out of it and this becomes a problem because it reduces the volumetric efficiency of our engine.
The engine simply can't breathe, it's like having a really restrictive exhaust system on our car. So what we're looking at here is our exhaust manifold pressure. And I think this is probably one of the key metrics when we're looking at turbo performance and validating a turbocharger sizing. So we can see there that in particular at 7000 RPM we've got 18 psi of boost pressure in the inlet manifold. Remember that in order to achieve that we're going to end up with around about 28 psi in the exhaust manifold.
So that's quite a significant increase over our boost pressure. And we see the next line down here, which is listed as engine delta pressure. This gives us essentially exactly that, the difference between our exhaust manifold pressure and our inlet manifold pressure. And we can see that at 7000 RPM, our exhaust manifold pressure is 10 psi higher than our inlet manifold pressure. Now the upshot of this is, and this is where the system does have its limitations, is that when we've got our exhaust manifold pressure that much higher than our boost pressure, it's going to reduce the volumetric efficiency of the engine as I've said.
So realistically what we would probably need to do is come back up here and take a bit of an estimate on the actual VE and maybe that's going to nose over, maybe it's not gonna be 100% anymore, maybe it's gonna be more like 90%. Actually I'll also just mention, for those eagle eyed you've probably already picked this up. I did mention this but then I didn't do it. Once we've got a compressor match here, what we do wanna do is come through and look at the actual values that we're getting in terms of our compressor efficiency. So for example here our 0.1 where it's sitting on this 0.6 or 60% efficiency line, for 0.2 we are somewhere around about, let me see, 0.68, 0.66, we're around about 66% efficient.
Our third point there, 72% efficient. So what we wanna do is basically take those numbers there and then we want to drop them into our compressor efficiency here. So that's also going to affect those calculated outputs so we want to do that before we take too much notice of our calculated outputs. Alright if you're still with me, we're gonna go through a couple more examples so now what we're going to do is have a look at that same engine, only this time we're going to try an So this is a next size up in the BorgWarner range. So you remember that I said the 7163 we were really pushing the turbo very hard, we're right at that choke point at our 7000 RPM point.
So it's gonna give us great bottom end response, we're gonna get good boost response but the turbocharger was probably gonna fall over at high RPM. So what we'll do here is we'll have a look at our compressor match this time with the 8374. So we can see that this gives us a slightly better match. We are now getting pretty close to our surge line there at low RPM. What we can see here as well, going through that same setup, I'm not gonna do all of it, but going through that same setup with our turbine map, you can locate all of our points, our match points on the turbine sizing selector and we're going to be able to see that in this instance with the 8374 we should be able to see somewhere around about 10 psi of boost by 3000 RPM.
And that's got our wastegate essentially completely closed, we've only got about 1.6% wastegating so really the wastegate in that instance would be completely closed. The last application I'm gonna have a quick look at here is we're gonna have a look at the same engine, this time fitted with a larger turbo again. We're going to have a look at our compressor match and we've jumped up to the 9180. So with a 9180 we've now got our points matched really well through the mid range. We're no longer near the choke line on our compressor map.
So this is gonna really aid our high RPM performance. So I'll just come back up here. You'll note here that I have in this application raised our boost pressure targets, we're now targeting 24 psi of boost pressure. You'll also notice that I've dropped our boost pressure at low RPM. Now our 9180 is not going to be able to spool up as well as the smaller turbocharger so that's a given.
But we do notice here that we do need to be careful because if we drive that turbocharger much harder than we are right now, at low RPM, we do risk ending up running that into surge. The reality is it's not likely to be much of an issue on a 2.6 litre engine, we're not going to get the sort of exhaust gas energy in water that we need in order to drive that turbocharger that hard. Alright so what we can do there as well is get some idea, and BorgWarner go over this in their YouTube videos, I'm not gonna dwell on it too much. We can get some idea of what the effect is going to be by swapping to a different exhaust housing AR. So let's come down to our turbine maps.
So at the moment, again I'll just try and open this up a little bit. So we are looking at the 9180 using the 1.05 AR exhaust housing. So this is the line that we've got all of our points nicely matched on. They also do a 9180 with a 1.45 AR exhaust housing. So what we can do is basically see what the effect of changing between the 1.05 and the 1.45 would be.
So to do that we've got all our points plotted at the moment, I'll just shrink this back down and see, I'm not gonna do every point because we'll be here for an eternity. Before we do this, let's have a look at our calculated outputs again. And the key calculated output that we wanna look at here is our exhaust or engine delta pressure, or in other words we know we're talking here about our exhaust back pressure. We can see we've got 28 psi of exhaust back pressure. 24 psi of boot pressure.
So our delta is minus four psi. That's actually pretty good, that's a pretty good number, we're not offering a lot of restriction and that's going to help our engine make a lot of power. However let's see what happens when we change that. So let's look just at that point six. And what I'm going to do is just move that up to our 1.45 line.
Got that nicely there. If you're watching there, as we move that up, we see that our required wastegating reduces this because we don't need to bypass as much exhaust gas around the turbocharger. Now if we look at our calculated outputs, we can see that our exhaust back pressure has dropped from 28 psi I think it was, down to 26.4 psi. Our delta pressure across the engine has dropped from minus four psi to minus two. So we are reducing that back pressure, this is allowing the engine to breathe more freely.
So this in turn, you'll remember I said, improves the volumetric efficiency of the engine, so we can get an idea of how that's going to affect the engine performance. At the same time, while we are doing all of that, we're also able to see, I obviously wasn't changing our low RPM 3000 set point. But we were going to be able to get an idea of what sort of boost pressure is going to be likely at those lower RPM ranges. Alright so obviously it is a complex tool there, I've given you a lightening quick tour of that tool. But as I've said, if you do wanna learn more, please check out those tutorials on the BorgWarner YouTube site.
It will make it really easy to understand how to use that. And it's a good way of just playing around for a few hours and getting a feel for what each of the different turbochargers in that range are likely to perform like on your given engine. And most importantly by doing that, you're gonna make sure that the compressor map that you're going to be operating nicely in a good range inside of that compressor map, hopefully you might even have a little bit of head room for if you want to lean on that combination a little bit harder in the future, and it's also gonna help you with sizing your turbine wheel. Alright I will jump into questions really shortly, so this is a good time to just mention and it looks like we've got a hell of a lot there already. See if we can get through all these, might be here for the rest of the day.
So if you do have any more questions, maybe not too many more, please ask those in the comments and we'll get into those in a second. I was actually going to do this and I completely forgot so this is a good time to do so. What is also, I've actually changed that, what is also worth mentioning is if you are looking at the difference between a single scroll and a split pulse exhaust housing, you can kind of get an idea of how that's gonna work. Again, this is described in a bit more detail in the BorgWarner videos. But what that will do is it's going to affect the turbine efficiency.
And what you can do there is basically take a bit of an educated guess at an increase in these turbine efficiencies. So again on BorgWarner's recommendations they've recommended increasing the turbine efficiency at low RPM from maybe 75 up by about 15% so we'd take that up to 90. Maybe we'll go another 10% at 4000 RPM so we'll take that up to, oh we've actually already done that as well, 83 and then maybe we'll go to 80% at 0.3 So when we do that, we can see how that's going to affect the ability of the turbocharger to produce boost pressure. And we can then manipulate what exhaust housing we're operating in and see what that's going to result in, in both our boost response as well as our turbine inlet pressure. So it's quite a powerful way of really getting a solid idea of how that turbo's gonna perform before we actually ever hand over any money and go to the trouble of fittting the turbocharger.
Alright the last topic I'm gonna go through here is validating the performance of the turbocharger. Because as we've seen here on MatchBot, we are making a lot of assumptions there and we don't have all of those pieces of data necessarily. And if you are gonna get serious about making sure you're getting the most out of your turbo, it is worth considering adding some sensors so you can actually data log and validate the performance. If you do end up updating your turbocharger at a later point, you're then gonna have a lot of solid data to work from, rather than sort of just a gut feel so to speak. So in particular the pieces of equipment or sensors that I would suggest adding in would be starting with an exhaust manifold back pressure sensor or turbine inlet pressure.
Now this allows you to look at the ratio between turbine inlet pressure and inlet manifold pressure. And for me I kind of use this as a rough line in the sand for sizing the turbocharger. Basically the lower that ratio is, the more performance we're going to get out of our turbocharger. The freer flowing our engine is. So basically the lower our exhaust manifold back pressure is, the more free flowing our engine is going to be, the higher the volumetric efficiency, the more power we can make.
So a really good example of this is in our drag racing engines, we were aiming for a pressure ratio below 1.0 So in other words we wanted our turbine inlet pressure to be lower than our boost pressure. Once we got to that point, this is sort of almost where our turbocharged engine starts acting like a naturally aspirated engine, and we can start adding more aggressive cams with more overlap without the downsides we see with a more restrictive turbocharger. So the problem with a very low pressure ratio like this is it doesn't provide a lot of exhaust gas energy to drive the turbocharger so in turn we see a higher boost threshold. So it wasn't uncommon for example with my own two litre drag engine, I wasn't seeing full boost until 7000 RPM. That was OK for me because I was launching at 7800 RPM and we were running it out to 10500 RPM with a sequential dog box and flatshifting.
The turbocharger never had an opportunity to drop out of its useful power band. With a more responsive setup, we're probably going to be looking somewhere in the region of a pressure ratio of 1.0 to 1.5 times boost pressure. So that's where if we were running 10 psi of boost pressure in our inlet manifold, we'd probably be expecting to see maybe somewhere in the region of 10, 12, to 15 psi of exhaust manifold back pressure. It's not a bad place to be, we're still gonna get a great response from our engine and we're still gonna make great power. If we look at what's happening in a factory turbocharged engine where the manufacturers are really focusing on low end response, at the sacrifice of high RPM performance, it's not uncommon to see the exhaust manifold pressure somewhere in the region of as much as two or more times boost pressure.
So if we had 10 psi of inlet manifold pressure, we might see 20 plus psi in the exhaust. So this is problematic because it really hinders our high RPM performance and this is why, if you look at the boost curve in a lot of factory turbocharged cars, almost inevitably you see a peak in boost at low RPM, around peak torque, and then the boost will tend to taper away as that exhaust manifold back pressure gains. The other thing that's really useful, if you wanna start plotting your points or operating points more accurately on one of those compressor maps just to validate how the turbo is performing, it's nice if you've got a compressor or turbo speed sensor. Generally these were incredibly frustrating and difficult and expensive to fit. These days, most of the performance turbo manufacturers are making our life really easy.
WIth BorgWarner as well as Garrett with their new G series turbochargers, there are ports already on the turbocharger for mounting these kits so it's as simple as taking the compressor housing off, drilling through the end of that hole, and fitting a kit that you can buy from the supplier so that makes it really easy and then you can know exactly what your compressor speed is, turbo speed is. Particularly for some of these turbos, BorgWarner turbos are reliable as hell as long as you stay under their maximum critical speed, so you do wanna know if you're getting close to that critical speed in an application where you're really pushing that turbocharger hard. Of course then we can get a little bit more sophisticated as well and start measuring things like the pressure drops across our inlet system, across our intercooler, so we've got all of that data. Sometimes that can actually shock you into modifying these components and getting a nice improvement in performance that you didn't even know you were losing. And lastly our air temp you can actually measure what the air temp is coming out of the turbocharger, you can measure the air temp out of your intercooler, start getting some data on the efficiency of how well your intercooler is doing its job.
Alright guys it's been a really long webinar but looks like we've got a bunch of questions so we're not done yet, let's get stuck into these and I'll see how many of these I can get through, hopefully I can answer them all. Ben has asked, probably a little bit off our turbo topic, this was from our pre show, regarding the Toyota 86 and overheating. Yeah just talking about the under train and the body panels. Yeah we've honestly tried a lot, we've been dealing with Toyota 86s overheating for about sort of five years now and I can assure you we've done just about everything that you could sensibly think about. But if you're following our social media channels, we're gonna be covering what we do and how well it works so you'll get an idea of what the fix hopefully that we find is.
Craig has asked, so I've had my head ported and have the flow bench results, how do I use those in the calculator? OK so it's not really just a case of flow bench numbers on your cylinder head. Really what we need to know is volumetric efficiency numbers of the engine and that goes a little bit further than just flow numbers of the head, this takes into account the whole operation of the engine. And flow numbers, while I am not a head porter, flow numbers are useful but they do not tell you the entire story about how a given cylinder head is going to perform. The reason for this is that air flow and air velocity are both very very important. So a mistake that a lot of beginning head porters make is thinking the old story of bigger is obviously better.
So they'll hock out the ports to a massive size, they see a massive improvement in outright air flow numbers but what this does, particularly at that low RPM is it just destroys air speed. And when you actually put that cylinder head back on the engine and dyno it, what you find is that you may have increased the performance at high RPM but you've now got an absolute dog through the low RPM and mid range. So unfortunately cylinder head flow numbers on their own are not enough to really help you with these calculators. Adam has asked, can a turbocharger improve fuel efficiency? OK a complex one there. I would say basically the simple answer is yes it can and this is why we are seeing a drive now with OE manufacturers, they are downsizing engines and adding turbochargers and that combination with a small capacity engine and boosted, you're seeing an improvement in the fuel efficiency.
For our particular performance instances though, that's probably not particularly relevant. And generally when we are adding forced induction to an engine, our break specific fuel consumption is going to increase compared to a naturally aspirated engine but we are of course going to be making a lot more power. So I don't know if that really specifically answers your question but it is a bit of a tricky one to answer. Paulsen has asked, is the power measured at the flywheel or rear wheel horspower. For example a turbo rated at 1200 horsepower, is that at the flyweel or the rear wheels.
OK so the ratings for turbochargers are always in engine power or flywheel power number. And you do need to be really careful about trying to relate them to wheel power numbers. The reason for this is simply if you put your car on five different dynos, you're likely to get five different numbers and sometimes these numbers can be vastly different so yeah it's always talking about flywheel values there. Barry has asked, maybe this is for a webinar all to itself but can you explain corrected turbine gas flow charts and how they correlate to tubrine housing AR? Probably not something that needs to be dealt with in a separate webinar, but yeah Garrett produce turbine flow charts with corrected mass flow and this is basically corrected for the turbine temperature, the gas temperature. So if you have your turbine inlet temperature, you can actually go through the process of calculating that mass flow number out.
Maybe you could ask the question about that in the forum and I can try and deal with that in a little bit more detail. JP's asked, single scroll versus twin scroll versus V band type rear housings pros and cons. Dealt with that already in the webinar, single scroll versus twin scroll, the twin scroll well designed should provide an improvement in low RPM boost response. Alternatively you can step up to the larger AR housing. Without sacrificing boost response you're gonna make more power.
The V band type housing, the advantage with these is just the simplicity of working on the turbocharger and on the engine. These days there are the availability of both split pulse and single entry V band housings as well so you don't necessarily in all applications need to be using a T4 style four bolt flange. With our race or competition vehicles, we're going to be working on those engines a lot more frequently, parts come off, parts get put on. So for me the V band housing is almost a must have, I really like that style of exhaust housing, really quick and easy to work on. Tony has asked, can we get an opinion on the EFR versus the G series and which may be better? Unfortunately no you can't because at this point I have not had the opportunity to test our any of the G series turbochargers.
What I'd say is that up until probably the last few years, I think BorgWarner with their EFR range have really shown an improvement and a performance advantage over Garrett. Maybe not a massive significant advantage but an advantage none the less. Garrett with the G series I think this was their basically their sort of throw down to BorgWarner and these turbochargers are aimed to be operating on a competitive footing with the EFR turbos. The evidence I've seen from dyno sheets does look really compelling. These G series turbochargers look like they're doing a great job.
But yeah haven't actually used one myself. We are going to be running a G series on our SR20 VE engine so we wanna be doing exactly that. And we're working with Garrett on that. We are running at the moment a Garrett GTX3076R Gen2. In its own right definitely no slouch of a turbo and a pretty good match to an SR20 VE motor for our power aims.
What we're going to do is get some hard data on that. It's gonna be instrumented with all of the sensors that I talked about in the webinar. Then we will be swapping to a turbo that they've got coming out very shortly, their new G30 series turbo and this will give us a really good opportunity to do a direct back to back. It's not often you get the opportunity to test just a single change such as that with a turbo so we're really excited about getting that information. Ken has asked, EFR versus G series, pretty much same question there.
I'm curious about the twin scroll setups on smaller capacity engines, like a 1.6 litre 4AGE. Does the twin scroll only become advantageous when you come into the bigger turbo sizes such as the GT30 size frame? No the theory of operation and the advantages are gonna be there regardless whether you're talking about a 1.6 litre engine or maybe a three litre, six cylinder engine. The only real hassle factor there is your exhaust manifold design does need to accommodate the split pulse housing and the firing order of your engine. Terry has asked when a person says they have a 90 millimetre turbo, is that measurement at the inducer or the exducer of the compressor wheel? So when we're talking about that, the measurement that's most often used there is going to be the exducer diameter. And we're seeing a lot more turbochargers rated on their compressor diameter and we see the likes of BorgWarner there with their EFR, they basically give us the OD of the compressor and the exhaust wheels in the name of the turbo, let's say 9180, that's what we've got there.
CMax has asked, thoughts on the HX35 turbos from Holset. To be more accurate the HX35 with a nine centimetre hot side. OK the HX35s, it's a turbo that unfortunately I haven't had the opportunity to ever use. They do appear though however to be an incredibly popular turbocharger and the results I've seen for them seem to be pretty great. They are also quite a cost effective option.
I mean today we've talked a little bit about the BorgWarner and we've talked about the Garrett turbochargers and while yes both are great turbochargers, both use ball bearing technology and they are quite an expensive unit. So that does need to be factored in as well. Jimmy Neutron has asked, where can I find a turbine inlet pressure sensor for datalogging? OK so the pressure sensor we use is actually nothing special there. Generally we're just going to be using a zero to 150 psi gauge pressure sensor. The tricky part is how we plumb that up to the exhaust manifold or turbine housing so that it's not damaged.
Obviously we've got exhaust gas there that could be around the 900 to 1000 degrees C mark and the sensor's not gonna last very long if we just screw it into our exhaust manifold. So with this what we want to do is remotely locate the sensor and the general way of doing this is to use copper tube and we're going to bend our copper tube up into a bunch of little circles and that's going to then run out to our sensor and the length of copper tube is going to basically take all of the heat out of that exhaust gas before it reaches the sensor. It's also a really good idea to make sure that the sensor is mounted above the point in the manifold that you've taken that exhaust pressure source from so that we don't end up with moisture tracking down into the sensor. C Marion has asked, do external wastegates have an advantage over internal wastegates, particularly on the EFR range of turbos? Yeah there can be advantages. So really the main one is probably, I'll step away from the EFR range for a start.
Traditionally what we've found is that as we step into larger sized turbochargers, the external wastegate just becomes a qualm and it's not really whether there's an advantage or a disadvantage, we just simply don't have any capacity for an internal wastegate on the exhaust housing. So this has changed obvioulsy a little bit. BorgWarner with their EFR range made a big play to including internal wastegates on their turbochargers. But the important thing to understand is that these turbine housings were designed from the outset for the internal wastegate actuation. So they've got nice flow paths into the wastegate, as well as wastegates that are properly sized.
So the EFR range, it's a little bit difficult to compare that to a conventional turbocharger. There are still some hassle factors I guess I'll say with using an internal wastegate on the likes of an EFR turbo. And that is because we still have to mount the actual actuator somewhere. And generally we're going to always be needing to clock the turbo housings relative to each other in order to get everything located exactly where we need it for our particular installation. And sometimes that can be limiting with where abouts that wastegate actuator can go.
Really good example of this is on our turbocharged Toyota 86 we run a BorgWarner EFR 6758 with a T25 flanged exhaust housing and the internal wastegate. It works really really well but the problem is the angle that the wastegate actuator comes off, the place that the wastegate actuator really should be would be essentially scraping along the ground. So we've had to make some compromises there to mount the wastegate actuators in a way where it's still gonna operate correctly, but it's not gonna end up interfering with the ground or anything under the car. In very high horsepower applications, I have heard of some people still running into problems with boost control with the internal wastegate EFR turbos. This is third hand information so take it with a grain of salt.
I personally have not seen this first hand. Our next question is, I think everyone would like to know, if you choose a turbo size by the amount of cylinders and displacement I assume? OK so well hopefully this webinar has cleared up that there's a lot more to it than that. That's a pretty simplistic view and I understand why you ask that question because if we go to any of the turbo manufacturer's websites, there's always going to be a power range and a capacity range that that turbocharger's suited to. You could think of this as a really coarse way of sizing a turbocharger for your engine but there's a lot more that we need to consider before we fine tune that selection and actually get down to the exact turbo we're going to fit. Ash has asked, there's a coalition between the inlet and the exhaust housing, is there a coalition between, correlation I think you're going with there, between the inlet and exhaust housings and wheel sizes? I've heard of people putting bigger intake wheels and housings on a turbo but retaining the rear housing and housing AR.
OK so yeah there is. These, what you're talking about there is something that was very very common probably at the start of my career where we didn't have access to the range of specialist performance turbos we do now. So quite a common option was to take a factory turbocharger, maybe fit a larger compressor wheel. Now the reason we would do that, why we'd fit a larger compressor wheel, as we've already discussed, to make a certain amount of power, we need to be able to flow a certain amount of air and there's a limit on how much air a given compressor can flow. So by going to a larger compressor, that can increase the air flow potential for that wheel.
So that fixes one side of the turbocharger. The problem however is that the turbine and the compressor wheel do need to be properly matched. If they aren't, and this is an issue that I have seen several times in my career, where a compressor wheel is mismatched to the turbine, we can end up finding that we drive that turbocharger into surge. So the way that that was dealt with with a lot of these hybrid turbos is we fit a larger compressor wheel, we then perform a back cut to the turbine wheel, it's pretty primitive really these days but as its name implies, it's essentially, a portion of the turbine wheel is ground away which improves air flow through it. It makes the turbo, basically we don't provide as much energy to the turbocharger, this helps us get away from that surge problem.
And that is kind of one option for a hybrid turbo. These days we are lucky to have the access to a lot of these performance turbochargers where we have got well matched combinations between compressor and turbine wheels. Guys we are gonna have to call it there. I've still got a bunch of questions here and I am gonna apologise right now to those guys whos questions I haven't been able to get to but we have simply run out of time there. For all of our HPA members, if you do have other questions that crop up after this webinar has aired, please feel free to ask those in the forum and I'll be happy to answer them there.
Alright guys thanks a lot for joining us and I will see you all next week. Now for those who are watching on Facebook today, looks like there is a bunch of you. Some really great questions that have come out of Facebook. This is just a little insight into what we put on every week for our HPA gold members. Now if you are interested in learning more and maybe becoming a gold member, then you can purchase gold membership which will give you access to these webinars as well as our archive of existing webinars, there's almost 200 hours of content in our webinar archive.
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