150 | Tuning for Economy vs Performance
In this webinar we’ll discuss the concepts of tuning for maximum power and maximum fuel economy and see how we can typically blend these aims within a single map. We’ll also discuss some of the implications of a specialised map designed to offer a fuel economy advantage for the likes of an endurance race application.
- It's Andre from High Performance Academy here, welcome along to another webinar. In this webinar we're going to discuss the concept of tuning for fuel economy versus tuning for engine performance. This is a common question we get asked about, whether we need to have two separate maps in our ECU. One that we can switch between when we want to take the car to the racetrack for maximum performance and one that we can use in the car on the street when we're really most interested in fuel economy. So we're gonna delve into that concept and we're gonna see that that's not necessarily a requirement.
We'll have a look at some demonstrations as well to see exactly how the air fuel ratio that we choose to run affects the performance of our engine. Now as usual we will be having a question and answer session at the end of the webinar so if there's any concepts that I discuss in the webinar or any of the demonstrations that I do, that you'd like me to delve a little bit deeper into or explain in more detail, or for that matter any other concepts relating to today's topic that you'd like me to talk about, please ask those in the comments or in the chat and the guys will transfer those through to me at the end of the webinar. OK so we've started by saying that a lot of novice tuners believe that we do need to have two maps. One for fuel economy and one for maximum power. Now that's honestly not the case.
And one of the keys here is that when we're tuning any ECU we have a three dimensional table for our fuel delivery. And that three dimensional table uses RPM as one axis and we've also got a load axis. So depending on exactly how the engine has been configured this is most often in an aftermarket ECU going to be manifold absolute pressure. It could also be throttle position if we are running it on alpha n. Now the key point here is that we can then target a different air fuel ratio depending on what our current load is.
So what I mean by this is when the throttle's almost closed when we're at idle, or when we're at cruise, under those conditions where we're really not that interested in maximum power, what we can then do is focus on an air fuel ratio that's going to give us maximum fuel economy. When we go to wide open throttle though, obviously under those conditions we're more interested in making maximum power from the engine and we can choose a suitable air fuel ratio that's going to provide that while also providing us with a safe and reliable engine. So just to see exactly how that works, let's just jump across to our Link G4 Plus ECU for a moment. So this is the ECU that I am going to be demonstrating our webinar on today. The concepts in this ECU will still relate to just about any aftermarket ECU you may be tuning.
So right here we've got our main fuel table, or actually more correctly this is actually the volumetric efficiency table 'cause this is currently running in a V or modelled fuel mode. So the 3D concept is what I was talking about. We can see that we have manifold absolute, or actually manifold gauge pressure on our vertical axis there, and we've got our engine RPM on our horizontal axis. Now because this particular ECU is using a volumetric efficiency based fuel model, we actually make our air fuel ratio target changes across in a separate table, this is our air fuel ratio target table. So again we've got exactly the same axes here.
We've got manifold gauge pressure, and then we've got our engine RPM, engine speed, on the horizontal axis. So we can see here that as we move up and we increase the load on the engine, we can target a different air fuel ratio. So what you'll see in this particular table is there's a block of values here that are set to lambda 1.00 so I will be talking in this webinar predominantly in units of lambda, so I apologise for those of you who are more familiar with working in units of air fuel ratio. For pump gas all we really need to remember though is lambda one is our stoichiometric air fuel ratio of 14.7:1 Lambda one actually regardless of our fuel is always the stoichiometric air fuel ratio. So this block of numbers that I've got here covers the main areas that we're going to be operating the engine in under idle and cruise conditions.
So these are the areas where I was just mentioning before, we're more interested now in getting good fuel economy from our engines. If we're an OE manufacturer we're also obviously really interested in minimal emissions from the engine. But for our case we're really looking here at getting good fuel economy. On the other hand though when we got up to wide open throttle our target changes quite dramatically. So you can see particularly in our top row here of our air fuel ratio target table, which is where we're going to be operating at when the engine is at wide open throttle, you can see for the most part I'm targeting lambda 0.90 So this is a much richer air fuel ratio than our lambda one target.
So this is an air fuel ratio that's going to be much more suited to making maximum power from our engine. So this is the key point here, we've got that three dimensional table there that we can move around in and we can choose the air fuel ratio to suit the current operating conditions, whether we want maximum power or we're more interested in fuel economy. Now with all of that in mind we do need to talk a little bit about why we need to change those air fuel ratio targets depending on what we want out of the engine. So for instance let's start by talking about the cruise area of the fuel table. So under these conditions we're cruising along the open road, the freeway, the motorway, and we really only have that throttle barely cracked open.
We're not requesting very much power or torque from the engine and under these conditions, this is where we want good fuel economy. Now the important factor here is because the throttle body is predominantly closed, we don't have a lot of air and fuel entering the combustion chamber so we're not actually combusting a lot of air and fuel. Now in turn the key point that we need to understand here is this also is not creating a huge amount of heat inside the combustion chamber. So it's quite satisfactory for us to choose an air fuel ratio at cruise and idle around that stoichiometric air fuel ratio lambda 1.0 14.7:1 for pump gasoline. Or as we'll see a little bit later, even potentially a little bit leaner than that.
Now when we go to full throttle, things change quite dramatically. Under full throttle operation now the driver is demanding maximum power from the engine. We want every absolute possible newton metre of torque and kilowatt of power out of our engine to make it accelerate as fast as we possibly can. Now at this point we've got that throttle wide open. So what's happening now is we've got a lot more air and a lot more fuel entering the combustion chamber, and under these conditions we're going to need to target a richer air fuel ratio.
Now that term richer means that we're adding proportionally more fuel to mix with the air that's entering the cylinder. And there's two reasons why we're going to be targeting that richer air fuel ratio. First of all because we want maximum power, we want to be very sure that under the turbulent nature of wide open throttle operation, we are injecting sufficient fuel so that all of the available oxygen inside the combustion chamber is being mixed with fuel and combusted, so that's the key. It's not the fuel that really affects the power the engine makes, it's the amount of oxygen making its way into the engine. Our job as the tuner is simply to mix the air, the oxygen that's entering the cylinder, with the correct amount of fuel so that we can combust all of it.
So that's one reason why we would target a slightly richer air fuel ratio. However there's another subtle aspect here which is probably even more important. Now under the wide open throttle operation, because we are combusting so much more fuel and air inside the combustion chamber, this tends to generate a lot more heat. And this can potentially be dangerous to the reliability of our engine. If we have too much heat going on inside the combustion chamber, this could potentially end up damaging our engine components, could melt pistons, it could melt valves, and the other aspect here is that the higher the combustion temperature goes, the more prone our engine becomes to suffering from detonation so we do need to be very careful with managing the combustion temperature.
So while it might sound a little bit counter-intuitive, by actually injecting a little bit of additional fuel that's essentially passing through the combustion chamber unburned, that additional fuel has the effect of removing temperature out of our combustion chamber, cooling that combustion charged temperature, and helping ensure that our engine remains reliable. Now while I've mentioned that the air fuel ratio, the emissions I should say probably aren't our biggest driver when we are tuning in the aftermarket. Certainly for the OE manufacturers, the emissions is probably their biggest concern. So particularly when you're running your factory car at idle and cruise, the OE manufacturers are absolutely trying their hardest to make sure that the emissions coming out the tail pipe are minimal. If that's not the case they're going to struggle to get that engine into production in the first place, so this is really their key driver.
So fuel economy actually takes a back seat to the emissions coming out the tail pipe. We'll just have a quick look over on my laptop screen at the moment. And what we've got here is a graph of how the emissions at the tail pipe vary with our air fuel ratio. So just to confuse matters slightly, this time we are actually using units of air fuel ratio on the horizontal axis of our graph here. So we've got this particular point here, if we can draw down through there, this is our stoichiometric air fuel ratio of 14.7:1 and we've got the various components that make up our tail pipe emissions.
So we can see we've got carbon dioxide, we've got carbon monoxide, we've got oxygen, we've got hydrocarbons, and we've also got oxides of nitrogen. Now what we can see is that as we move rich which is off to the left, some of these components, some of these emissions components decrease and others increase. Likewise as we move lean which is to the right of our stoichiometric air fuel ratio point, we see exactly the same effect. Some of the components increase and others decrease. What we actually find, which is the key point, why OE manufacturers are always running their cars at 14.7:1 at that stoichiometric air fuel ratio, is that at the stoichiometric air fuel ratio, this is where the combined total of our tail pipe emissions are minimal.
So there's advantages to some of the tail pipe emissions by going richer, advantages to others by going leaner. But at 14.7:1 or lambda 1.00, this is where we're going to get the net minimal emissions. We'll also find that on the same note, we'll see that OE manufacturers are also fitting our engines with catalytic converters in the exhaust system. And what we'll find is that the factory ECU will actually be commanding the air fuel ratio to constantly dither backwards and forwards across that stoichiometric air fuel ratio, and this is to actually make the catalytic converter work properly and reduce the tail pipe emissions further. So that is why we see that under closed loop conditions in idle and cruise, all of our factory cars will run at 14.7:1 Much and all as we'd like to think that that is because it provides minimal emissions, the reality is actually because this is where we're going to get minimal tail pipe emissions.
So what this means, and we'll see this a little bit later is that we can get a small improvement in fuel economy by targeting a slightly leaner than stoic air fuel ratio during the cruise operation. Now I will also mention here, there's a caveat to that, this will affect your engine emissions, so if you are tuning or operating in a country or a city where there are emissions rules that you need to meet, this will affect your ability to meet emissions. So just keep that in mind. Also obviously as I've just mentioned, it will affect the ability of your catalytic converter to do its job properly which kinda doubles up on the same thing. OK so what we're going to do now is I'm going to get our Nissan 350z up and running here on our Mainline dyno.
And just to demonstrate the effect of the air fuel ratio that we choose to use, we're going to perform two torque optimisation tests. And with these torque optimisation tests, what we're going to do is change the air fuel ratio and we'll see how the air fuel ratio affects the way the engine is operating. So what I'm going to do, let's just jump into our laptop screen for a moment and I'll just talk you through what I'm going to do. We're going to start here by operating the engine at 2500 RPM and minus 60kPa. So what I'm going to do is I'm just gonna fudge the system here, we are going to be running a VE fuel model.
And you can see that our target lambda is displayed here, I'll just bring us up to our set point here, 2500 RPM. Just get nice and central on that. So you can see that our target lambda is staying there at lambda one. What I'm actually going to do, rather than dealing with this properly, for today's test I'm just going to make some coarse changes here to the value in the cell that we're accessing. So what I'm going to do here is I'm just gonna start by increasing this quite dramatically, and I'm going to get our actual air fuel ratio or lambda value all the way to 0.80 lambda.
So as I'm richening that number, or actually I can only get to 0.83 there, the largest number I can enter there's 150% but that's OK. Let's jump across to our dyno and I'm just gonna bring up our torque optimisation test here. OK so I'll just talk about what's on this screen. So first of all on the vertical axis here, we have torque in newton metres. So this is being registered by our Mainline dyno.
And on the horizontal axis here we have our lambda which is coming from the ECU. So this is going to be sent across from the ECU. I'll just clear this and what I'm going to do is I'm just going to start this test, and I'm going to lean out the lambda that the engine is running at and I'm going to lean the lambda out all the way, let's just increase this up as well, so we're not getting too much interpolation. I'm going to increase the lambda set point all the way up to lambda 1.1 and what we're going to get is a pretty rough idea of how the lambda that we choose to run affects the torque that the engine makes. So let's do that now, I'll start that test, and we'll just start reducing our value in our VE cell so this is gonna take a little while to go through here, and we'll see that our lambda starts to lean out, we're starting to come through 0.85 lambda.
And the whole time I'm doing this as well I am going to be keeping my throttle position nice and stable so that we're not really affecting the operating point inside the ECU. OK so we're coming through 0.9 lambda at the moment. And we'll just keep coming up here all the way through to lambda 1.1 Just try and make sure that we're staying in the centre of this cell here. OK so we're seeing at this stage that as I continue to lean out the lambda value that we're running at, just coming through lambda one now, we're seeing that our torque is dropping away. So I'll just keep going all the way through for the sake of completeness there until we get to lambda 1.1 We're just about there now.
OK I'll just back off the throttle. So obviously we've got a fairly squiggly line there and we're gonna have to use our imagination in order to sort of draw an average line through this if you like. But if we saw we started around about 54, 55 newton metres and we saw that as we leaned out from 0.80 lambda we saw that our torque did increase slightly. And the dyno's actually shown us here that we made maximum torque at this particular cell in our table with a lambda value of 0.91 We've made 58 newton metres of torque and then quite quickly after we leaned the air fuel ratio off further we saw the torque just start to plummet. So by the time we got to lambda 1.1 we're down to almost 35 newton metres of torque.
So we've got a big drop off. Now this 60 kPa cell that we've just performed that test in, this is probably a cell that we could expect to be accessing when we are under cruise conditions, so when we are just cruising down the road. So if we purely look here at our values from our torque optimisation test, we would see that if we wanted to make peak torque in that particular cell, we'd actually want to target 0.91 lambda. So a little bit richer, around about 9% richer than our stoichiometric air fuel ratio. So this is where we're going to be making a tradeoff.
Under these conditions what we actually want to do is focus on maximum fuel economy which is why under these conditions we would be more likely to run at lambda 1.00 than our lambda 0.91 where we're actually seeing peak torque. So if we were tuning an engine where we were solely interested in maximum torque everywhere, we didn't care about fuel economy, didn't care about fuel consumption, which is still a concern even in a race application sometimes, what we can see from this test is that we actually do see some advantage from tuning even the part throttle areas of our fuel table a little bit richer than our stoichiometric air fuel ratio or lambda 1.00 What I'm going to do as well is just perform one more test here and just to cement this, we're going to perform our second test here at wide open throttle at the same RPM. So what I'll do is I'll just clear the test that we've got here and we'll just set up some slightly different break points for our axis so that we'll actually be able to see the values, in this case we want to set our axes between about 350 and about 450 newton metres. Now under these conditions we'll try the same sort of air fuel ratio targets. We'll go from 0.8, maybe 0.85 to lambda 1.00 So let's just get us up and running for a moment and we'll make sure that we're in the centre of our 2500 RPM cell at wide open throttle.
Now I'll just mention here that for this test I have also just for safety's sake I've removed a little bit of ignition timing out of the cell that we are running in just so that we don't end up potentially doing any damage with knock occurring with a lean air fuel ratio that increases our combustion temperature. So I've just got our starting lambda there to 0.80 We'll just clear our test here. It should be a little bit easier to see as well because this time I am at wide open throttle the whole way. So let's start our test here, and I'll just lean out our air fuel ratio from our starting point at 0.8 lambda, we're coming through 0.82 now. And we'll see, at the moment as I'm leaning the air fuel ratio out here, we're seeing that our torque is increasing.
Another point I'll make here is that for those of you who aren't aware, for a given RPM, the engine's power is also directly linked to engine torque. So what this means is that as we increase the torque, we're also naturally increasing power. OK so we'll come through here in this instance, come out to lambda one now. I don't really need or want to go much leaner than that so I'll back off the throttle and we'll just have a look and a talk about our results here. So in this instance with our lambda set to 0.80 we can see that we started our test with around about 410 newton metres.
As I leaned the air fuel ratio out, we see we get a reasonably consistent increase in our power and in this case we can see that we actually made peak torque and hence peak power with a lambda of 0.93 What's probably also worth just mentioning here is that while we have seen peak torque at 0.93 lambda, in real terms we've got what is a plateau from around about 0.88 through to about 0.94 lambda. And once we go past about 0.95 though we can see the situation where our torque also drops away. So under wide open throttle conditions if we are interested here in peak torque, peak power, we can see that for this particular cell, our engine performed best at 0.93 lambda. However what we would also find in most instances is that this may result in a combustion temperature that could promote detonation and we may find that for safety and reliability we are actually better to target a slightly richer air fuel ratio than 0.93 Now I'll just mention here that this is going to depend on the engine that we are tuning. It's going to depend whether it's naturally aspirated or turbo charged, it's also going to depend on the fuel that we are running on.
But what we see is particularly as we move from a very rich air fuel ratio target like we started there, 0.80, and we lean out the air fuel ratio, what we see initially is that the combustion temperature does start to climb. And this is because we don't have that additional fuel in there passing through the combustion chamber unburned to help cool and control that combustion chamber temperature. However if we do continue to lean the air fuel ratio out massively we will actually get to a point where we start to see that exhaust gas temperature start to come down. The reason for this is we're simply not creating as much power, we're not combusting as much fuel and air in the combustion chamber and we're not creating as much heat. So hopefully those two tests just show you there how the air fuel ratio affects the torque that the engine makes, but probably just as importantly how that is only one aspect of what we may be interested in.
It's not always a case where we are going to be chasing peak torque. And the key takeaway here particularly if you are tuning a street car is that in a street driven car, you're probably likely to spend less than 5% of your time at wide open throttle. The majority of your time is actually spent at idle and cruise. So with our three dimensional air fuel ratio target tables or our three dimensional fuel tables, what this means is that we can choose a nice economical mixture under those particular conditions. As we've seen, yes we may be giving away a very small amount of torque using that leaner air fuel ratio, but under those conditions we're actually better off focusing on fuel economy and giving away that small amount of torque.
Now as the air fuel ratio of course does drop off, so we will also see that torque drops off. And what we find as we've looked at our emissions versus our air fuel ratio table previously, we saw that we got minimal emissions at our stoichiometric air fuel ratio of 14.7:1 on pump gas, that's lambda 1.00 What we will actually see is that as we continue to lean the air fuel ratio out or our lambda out beyond lambda 1.00 we will see that while our emissions do increase, our net emissions do increase, we can see a slight improvement in our fuel economy. This becomes a tradeoff because we've already seen that as we lean out the air fuel ratio, we see that the torque the engine produces drops away and this is something that's often overlooked. What we actually need to understand is that if we're interested in cruising at a fixed speed on the open road, that's going to require a certain amount of torque output from our engine. So it's all well and good going to these sort of cruise areas on our map and leaning out the air fuel ratio and seeing that we're getting a reduction in maybe the injector pulse width, indicating that we are injecting less fuel into the engine.
But of course as we've just seen in our two torque optimisation tests, as we lean out the air fuel ratio, we also see the torque drop away. So if we need a fixed amount of torque in order to maintain a constant speed on the open road, what you're going to find is that as you continue to lean out the air fuel ratio, the car will actually slow down. So in order to maintain speed we're going to need to increase the throttle opening in order to get us back to the same torque the engine was producing. So we need to be careful of this and we need to test this if we are going to see what the optimal air fuel ratio is for our particular application. I'm going to try doing this demonstration here on our 350z, please bear with me because this is an incredibly difficult test to perform accurately.
The reason that it is very difficult to perform accurately is what I'm going to have to do here is control the torque output while I'm performing this test by adjusting my throttle position. And in order to get really truely accurate data here, we need to maintain a very very accurate torque value. So this is very difficult to do on a chassis dyno. So I'm going to try this demonstration and it may well blow up in my face, and show some data that's not particularly useful, but I will take that risk on the off chance that it does exactly what I'm hoping it will show. And if it doesn't well you're gonna have to bear with me, you're gonna have to believe me to some extent and I'll be able to talk you through the results anyway.
OK so let's just jump across to our laptop screen again. And what we're going to do here, is we're going to just start, in order to make this really simple, we're going to start by setting up our closed loop fuel control. So this is gonna be a slightly different way to how I performed the last test. So we'll just enable our closed loop fuel control and this is going to allow the ECU to make adjustments to the fuel delivery in order to maintain a really accurate control over our lambda. So at the moment I'll just allow everything to come up to operating temperature.
And what I'm going to do is we'll go back to the same point we were operating in. We're going to go through to 2500 RPM and 60kPa. I'll just bring our speed up now. And what we're going to do is we're going to perform some logging here on our Link G4 Plus software, and we're going to be looking at the effect of varying the air fuel ratio on the injector pulse width. So before we do that let's just jump across to our dyno screen for a moment.
And my task during this test, we can see here we've got our torque output. So I'm just going to choose an arbitrary value here, I'm going to choose 60 newton metres, and I'm going to try through this test to control and hold our torque very accurately, or as accurately as I can, at 60 newton metres. So that's going to be challenging but we'll try our very best. Let's jump back across to our laptop software. And what we're going to do is head across to our AFR target table.
And this time I'm going to select a block of cells around the area we're running in, and I'm going to start by setting them all to 0.95 lambda. We can see straight away our measured air fuel ratio tracks straight to our target. Remember we've got closed loop fuel control sitting in there making any adjustments that are needed. I'll just get back to our 60 newton metres. We've got our logging running and what I'm going to do now is I'm going to lean out the air fuel ratio.
And each time I lean out the air fuel ratio, I'm gonna make a 0.1 step, and I'm going to make sure that I get back to our 60 newton metres of torque. So this is going to require me to constantly make very small increases in the throttle position in order to achieve that torque. So this is the same situation we're going to see if we are leaning the air fuel ratio out and we need, in this case let's say, we need 60 newton metres in order to maintain a constant cruising speed. So we're down to 1.02 lambda now, I'll just get back up to 60 newton metres. And we'll try and just, we're just moving around very slightly here but I'll get back down to 60.
Very very sensitive to small adjustments in our throttle here. OK we're 60 so I'll make another change. And 60 again. So we're at 1.04 lambda. Just get back to 60 newton metres again.
Go to 1.05 lambda. OK we're just dropping, our torque's dropping away quite rapidly now as I'm moving leaner so it's a little bit more of a challenge to stay at that same 60 newton metres. OK so we've gone up to 1.09 lambda, just going to stop our logging. Let's have a look at our logging, I'm too scared to look but hopefully this will help demonstrate the situation. OK so I'll just explain what we've got here first of all.
We've got our engine speed obviously that's a fixed value. Next we've got our throttle position. So you can see the general trend of what's going on here. As we've moved through our test from left to right, you've seen me constantly need to increase the throttle position in order to achieve that same 60 newton metres of torque. So what we're looking for here is, this is our effective injector pulse width.
So obviously when we've got a smaller injector pulse width we're delivering less fuel via the injectors, so this is a pretty good measure of where our economy is at its best. So if we look through here, if we start our test here, when we're sort of stable at 60 newton metres at 0.95 you can see our effective injector pulse width is 1.236 milliseconds. So I'll take another arbitrary point here. And at the point where we are stable here at 0.99 lambda, we've gone down to 1.18 milliseconds, so that's a nice improvement there. What I've tried to do here is I haven't made an adjustment to the lambda target until we are stable at our 60 newton metres.
So we're always looking, you can see our lambda here at the bottom, you can see it stepping up, and I'm sort of looking at our injector pulse width, just before I step it up, because this is where we're back to our 60 newton metres. So at 1.01 we're down to 1.15 milliseconds. We've got some ugly stuff going on in here. Let's see. We got to about 1.13 there, we've actually stepped up but that's not a very realistic test.
Just before we've stepped up from 1.035, we're down to 1.12 And at 1.05 we are sitting at about 1.10 What we find from there on in is we actually see our millisecond pulse width start to increase. And at the point where we're at 1.09 we're back to 1.166 So as I've said, an incredibly difficult test for me to perform. This is probably about as good as I can hope to achieve really here on a chassis dyno. So if I tried to really draw a bit of a curve through this and really average out the ugly stuff that's going on, we sort of get a situation where we see our injector pulse width come down, minimise, and then start to increase again. And while I certainly recommend testing for every engine, what I've generally found is that we find that our injector pulse width is minimised or in other words our fuel economy is optimised at a lambda value somewhere in the region of about 1.04 to 1.05 So you can get a small but measurable improvement in your fuel economy by targeting just that slightly leaner than stoichiometric air fuel ratio target.
The other tip there, because this is an incredibly difficult test to perform. So the other little pointer I'll give you, or guideline is if you are looking at your torque, and a given cell in your fuel map, and you're leaning out the air fuel ratio, I would lean out the air fuel ratio to the point where we start seeing our torque drop off by about 6% to 7%. And about that point once we go past that, you'll generally find that you see a net drop off in your actual fuel economy. OK we're going to move into some questions and answers soon so if you do have any questions please ask those in the comments or the chat and the guys will transfer those through to me. Now we have looked at a pretty run of the mill demonstration here for the purposes of our webinar, which is our Nissan 350z.
It could be a good demonstration for an average road car where we have concerns over both fuel economy and power. I would say that in most instances, that's probably what most tuners are really going to be worried about. Getting good fuel economy at idle and cruise while still not giving away any power under wide open throttle conditions. There are however some scenarios where our targets or our goals from the tuning project may be very different. So particularly there are some race applications, particularly in endurance racing, where we would prefer to give away a little bit of the engine performance, and prefer instead to gain an advantage in terms of our fuel consumption.
In other words we're going to improve our fuel consumption at the expense of a little bit of power. So how can we do this? Well the ideal, the obvious solution here is we're simply going to target a leaner air fuel ratio everywhere, particularly under wide open throttle conditions. Particularly under part throttle conditions in transient conditions. We're also going to be very careful of our transient enrichment there, we're going to use the bare minimum amount of transient enrichment we can get away with while still achieving good crisp throttle response. We're also going to be worried here about our overrun fuel cutoff which is often something that is not a consideration for circuit racing applications.
Now we do need to take this into account though, this strategy, if we are going to be tuning with a leaner air fuel ratio. Remember one of the reasons I said that we're going to be targeting a richer air fuel ratio, particularly under wide open throttle conditions is to help cool and control that combustion charge temperature. So if the combustion charge temperature is increasing, this is going to have the effect of potentially moving the engine towards knock, making the engine more sensitive or prone to suffering from detonation. So if you've got an engine, particular one that is sensitive to knock in the first place, if you're going to be tuning with a leaner air fuel ratio, you need to take that increased combustion temperature into account and you're going to potentially need to reduce your ignition timing a little way. That can go further to also reducing the engine power and torque of course.
Now I'll also just go back a little bit, the two torque optimisation tests that I performed, we were clearly only focusing on adjusting our air fuel ratio. In the real world there is an interaction between the air fuel ratio that we are running and the optimal ignition timing that the engine can take. So just to clear that up, I was only focusing there on demonstrating the effect of air fuel ratio, so for those of you out there who are thinking hey wait a minute I could probably also adjust the ignition timing, yes you're absolutely right, so those two tests were performed with fixed ignition timing. Now initially as we lean out the air fuel ratio we will see the combustion temperature start to increase. However if we continue to lean the air fuel ratio off dramatically we actually start to see the combustion temperature begin to drop again.
Essentially we really are just producing less power, we're combusting less fuel and air in the combustion chamber so naturally it's understandable we start to see the temperature drop away. And at some point if we continue further leaning out the air fuel ratio we may get to a point where we have the engine start suffering from a lean misfire where there really isn't enough spark energy to light off the lean air fuel ratio inside the combustion chamber. This is a problem with lean air fuel ratios, they do also become more difficult to combust. Now in particular just on this matter as well, we did actually discuss lean combustion with a formula SAE team a number of years ago when we were at PRI. So one of the tests that the formula SAE competitors need to go through is an endurance test.
And this is where they are scored based on their times around a lap but they are also scored very heavily on the fuel consumption that they need to use in order to achieve those times. So this is one of those areas where the teams may choose to take quite a sizeable power deficit in turn for an improvement in their fuel economy because the fuel economy actually weighs more heavily into the points. So in particular the team that we were talking to ran as lean as lambda 1.3 in some areas. So this just gives some sort of scope to the range of air fuel ratios that are potentially possible. I certainly wouldn't recommend that under all conditions, but yes there is quite a wide range that we may choose to use there.
Obviously under those sorts of air fuel ratios, lambda 1.3, we're going to see a really significant drop away in our power. And we do need to also consider if we are running very lean air fuel ratios, the effect on our ignition timing. As we've talked about previously,, as our combustion temperature initially starts to climb, particularly if we've got an engine that is very sensitive to knock, prone to detonation, we're likely to find that we're going to need to pull timing out of the engine in order to prevent it suffering from detonation. However as we continue to lean the air fuel ratio out dramatically, particularly in the instance, from the SAE example, where they may be running as lean as lambda 1.3 we'll actually find that we need to advance the timing in some cases as far as another five to 10 degrees in order to get the maximum performance out of that very lean air fuel ratio. OK we'll move into some questions now.
Our first question is, noticed the Toyota replacement turbo had a Kinugawa wastegate actuator, is that a Kinugawa turbo, and what are your opinions and thoughts on the Kinugawa brand overall? Fair question to do with our preshow, probably not particularly relevant to this actual topic. And I'll just briefly say in my own experience, I've had a few situations with the Kinugawa brand of turbos, they are probably one of the cheaper brands out of China, my personal experience has actually been really good with them. Spitman has asked can you give some insight on direct injection angle ignition AVCS relationship on how to achieve performance and miles per gallon? Really not in relation to this particular webinar. We will be running another webinar shortly on direct injection where that's probably going to be ideal for your particular questions there. So that brings us to the end of our questions.
Obviously not a lot of interaction there on that particular one guys. Hopefully that means that I've presented it really well and everyone understood exactly what I was saying. Regardless I hope that you have got something valuable out of this webinar and it's given you some more insight into exactly what the effect of the air fuel ratio is on the engine performance and in terms of how we can go about adjusting our fuel map and our air fuel ratio target maps to achieve the aims of both good fuel economy along with getting maximum power, maximum performance. So hopefully you've seen that these two aims can be achieved within one map, we don't need to run separate maps in order to achieve those two targets. As usual if you do have any further questions, please ask those in the chat and I'll be happy to answer them there.
Thanks guys, I'll look forward to seeing you all next week.