241 | Tuning for elevation change
One of the common questions we hear is ‘How do I tune for high altitude?’. In this webinar we’ll cover what actually changes and what you need to know, as well as some options you can use to get the best results. For this webinar we’ll be using our Toyota 86 running a MoTeC M150 ECU.
- Hey team it's Andre from High Performance Academy here, welcome to another one of our webinars and today we're going to be discussing what you need to keep in mind when tuning for large changes in altitude. This is a topic that we quite often get asked about and I think it's fair to say that it's a topic that is quite misunderstood in general. So today we're going to be talking about why we need to account for altitude changes in the first place and then of course look at the various techniques that are available and why one option may be better than another for your particular situation. As usual we're going to be having questions and answers at the end of the lesson so if there's anything that I talk about that you'd like me to dive into in a bit more detail, please feel free to ask those in the chat. So I think we're best to start off with why do we need to worry about altitude changes in the first place? And to be fair, it's not actually just altitude changes it's actually just generally changes in our barometric air pressure.
Now our standard air pressure at sea level is considered to be 101.3 kPa but as our weather systems changes even at the same fixed altitude at sea level, you are still going to end up with your barometric air pressure changing. Albeit if your altitude is relatively fixed where you're driving, where you're operating your car, where you're tuning, then you're not going to see the true effect of dramatic changes in barometric air pressure. It's really when we start looking at significant changes in altitude where this becomes more of a consideration. Now personally given that I've lived my entire life in areas where we don't see dramatic changes in altitude, in my past job where I had my workshop we were at sea level and basically it was very difficult to vary your altitude in that location by more than probably 500-600 ft. Here in Queenstown, we're currently at about 1000 ft above sea level and we do have some mountains here but our highest mountains are probably still in the region of about 6000 ft so still not getting a dramatic change in our actual altitude.
Although we do start to see some effects of barometric air pressure over even that sort of change. It's more a case where it was brought home to me when I was working on an unlimited hill climb car that competed at Pike's Peak and at Pike's Peak the variation in our barometric air pressure is dramatic, the peak of the mountain of course, about 14,100 ft. And depending on the atmospheric conditions on the day, at the start line we were seeing somewhere around about 80 kPa to 85 kPa, I can't actually tell you off the top of my head what the altitude at the start line is but that's about the barometric air pressure we see. And then at the top of the hill we're somewhere down around about 63 to 65 kPa so that's starting to be a significant difference in our barometric air pressure and something that we do need to take into account. So why do we need to take it into account? So the problem is that as far as our engine's concerned, it's basically an air pump and when we are looking at what the engine does during the intake stroke, basically we're measuring, or looking at volume flow, or volume of air but it's not really the volume that's important.
What we need to consider is the air density and that really defines how much mass of air will be ingested into the engine during the intake stroke. OK why that's important is because when we're looking at an aspect such as our fuel delivery, we're defining our air/fuel ratio. As it's name implies, simply the ratio between the amount of air in the engine and the amount of fuel being delivered. The tricky part with that that we need to keep in mind though is that the air/fuel ratio is a mass ratio. So it's the mass of fuel compared to the mass of air.
So if we're got a given volume of air going into the engine, as the altitude climbs, we're finding that for that given volume of air, it contains less and less oxygen, the air density is reducing. So getting one step further, if we don't account for the change in barometric air pressure, which infers the change in air density, then what's going to happen is that as our altitude increases, we're going to be injecting the same amount of fuel and as we do this, the air density reduces, the amount of oxygen in the cylinder reduces and of course we start to see our air/fuel ratio move richer and richer. While it's less important potentially this also affects our ignition timing as well because as the air density reduces, to maintain MBT timing, we generally need to advance the timing, we see that same trend in our ignition map anyway as we move from low load to wide open throttle, even at a fixed altitude. This is exactly the same as increasing or changing the air density inside of the cylinder. So those are the two main considerations there.
Another consideration that becomes very important for the likes of Pike's Peak though is that this also affects our turbo performance. So if we don't take this into account, we actually can find that we could be pushing a turbocharger dangerously beyond its limits. So just so we can sort of have an understanding of that, let's just jump across to my laptop screen again for a second. So this is just a generic compressor map that I found from a Garrett G30-900 turbocharger. So probably a lot of you have seen all of these before, if you want a little bit more detail on this we do have a specific webinar in the archive on turbo performance, have a look at that, you'll learn a bit more about it.
For this though, all I really want to note is the vertical axis here is pressure ratio. So this is the inlet manifold pressure essentially, divided by our barometric air pressure. So what this means is that if we are running a fixed manifold pressure at sea level and then we climb up to let's say 10,000 ft and we've still got the same fixed manifold pressure in the inlet manifold, you might be thinking, well manifold pressure's manifold pressure, that's the boost pressure the engine's running, that's all that matters. The thing that's easy to forget about is as we move up in altitude, for the same manifold pressure, we're actually moving up this pressure ratio axis because the divider in that, the barometric air pressure is dropping away. So we could be operating at sea level somewhere around about this area here depending of course on our boost and our barometric air pressure and we're right in the nice sweet spot of the turbo efficiency.
But we could find that at high altitude we end up right up here, if we try and maintain that same manifold pressure so that's really important, otherwise we can find that that could potentially damage the turbocharger. The other aspect with this as well that's easy to overlook is in terms of the entire engine performance, as we move up that pressure ratio we have to drive the turbocharger harder and harder to maintain the same manifold pressure, so to maintain the same fixed boost pressure in the inlet manifold, the wastegate as we climb up in altitude, ends up closing more and more and this creates more exhaust gas back pressure which in turn goes further on towards affecting the actual engine performance and ultimately its fuelling. So there's a lot of aspects that all end up sort of intertwined here that we need to understand. We'll just head back across to my notes for a second. So we've kind of touched on what needs to happen there or what, I should say, what will happen if we don't account for our barometric air pressure change, our fuelling's going to go rich, our timing, while less of an issue, is potentially going to be retarded from MBT and then we've got that consideration that I just mentioned there with our turbocharger performance.
Alright so how do OE manufacturers deal with this? The reality is that OE manufacturers almost always, not the only way of doing it but by far away the majority is that they use a mass airflow sensor for the scheduling the fuelling. I'm just trying to find my little picture here, right let's have a quick look at my laptop screen. So this is from our L98 engine in our GM Holden Commodore. So this is the mass airflow sensor fitted straight on the front of the throttle body. So the mass airflow sensor, why OEs like them so much, as their name implies, they directly measure the mass of air entering the engine.
And this is important because again, as I touched on, it's the mass of air that's the key to our fuelling and also to a degree our ignition timing. So provided that the mass airflow sensor is scaled correctly or calibrated accurately, it's telling the ECU exactly what mass of air is entering the engine and then the ECU can decide what pulse width to deliver to the injectors in order to achieve the correct air/fuel ratio. This also affects the timing, or where we are in the timing curve which I'll show you in a second. So the nice thing about the mass airflow sensor is that since it's directly measuring that mass of air, basically it accounts for barometric air pressure changes directly. Remembering again as the barometric air pressure drops, our air density drops so the mass of air being measured by the mass airflow sensor reports this directly.
So again if it's calibrated properly, it's doing all of the heavy lifting for us and the OE doesn't really need to worry about it. Now I will mention, yes of course there are OE manufacturers that use the speed density principle, we're going to jump into that in a second with the aftermarket tuning world. With the speed density principle, instead of directly measuring the mass of air that's entering the engine, instead we're calculating that using the ideal gas law and manifold absolute pressure becomes out load axis. When set up correctly, it can do an incredibly good job and still be very very accurate. However it does require a lot more compensations really to make sure that everything's tracking perfectly.
Alright so just to see how this all works from an OE manufacturer's perspective, we'll just jump into the HPTuners VCM Editor software and this is a three dimensional spark table. We don't need to really worry so much about fuelling because again we're just asking for a specific air/fuel ratio so unlike an aftermarket ECU, we don't need a three dimensional table like this, it's actually really simple in the GM engine control module, we just have a simple two dimensional table where we ask for a specific air/fuel ratio and again because the ECU knows what mass of air is entering the engine, it's got tables telling it what size the injectors are, it can straight away calculate what pulse to deliver to get that. So where our spark timing comes in a little bit different though is our RPM axis here on the horizontal axis, pretty typical to what we'd see on an aftermarket standalone ECU, the tricky part here is the load axis. Instead of manifold absolute pressure, we've got spark air mass and this is measured in grams per cylinder. So the important point to note here in the OE world is that the load axis for our spark table is also derived from our mass airflow sensor.
It's grams of air per cylindner so it's just reporting exactly how much air is going into the cylinder.. So the nice feature of this is that as our mass airflow changes due to barometric air pressure, we're actually moving around inside of this table as well. So at sea level, depending on the specifics of the engine, we might be down around this point here, maybe 0.88 grams per cylinder at 3500 RPM or thereabouts so we've got about 18 degrees of spark being delivered to the engine. At altitude though, again the density changes and we drop so we'd actually move up in this table here, let's try that again. We'd move up in this table here so instead of the 18 degrees we might be 21, 24 degrees depending on exactly what the barometric air pressure change is.
So this is how the OEs deal with it and it's all sort of basically taken into account automatically. On the other hand if we are using a speed density tuning principle then things do get a little bit trickier so we've got to look at the options that are available for us to do so. So if we have a quick look at a conventional ECU, this time we'll have a look at the Haltech Elite ECU. This is how we would normally set up our fuel table so in this instance they use RPM on the vertical axis and we've got our fuel load on the horizontal axis. It's called fuel load but essentially all that is is our manifold absolute pressure.
So this point, in particular here, 0 kPa, this is our atmospheric pressure at sea level, so this is for a turbocharged engine so as we move to the right there we're moving up into positive boost pressure. If we simplify this for a moment though and let's look at if we're just looking at our manifold absolute pressure and we're on a naturally aspirated engine. So in this instance, let's for a moment just assume that the 0 kPa row, that's as high as we can go so all of this out here to the right, let's just scrap that, we're not on a boosted engine for a moment. So if we are running at sea level and we are at wide open throttle, let's say we're at 3500 RPM, so we're right at this point here, and we can see that our volumetric efficiency at that point, 83.6% depending on how our ECU's set up. So that's going to define the amount of fuel that is delivered.
We're also going to be sitting in the 0 kPa zone for our ignition timing as well. Now as our altitude increases, what we're going to do of course is we're going to be moving back here to the left when we get up to wide open throttle. So instead of 0 kPa we might be -10, -15 kPa depending on exactly what the altitude and barometric pressure is when we're at wide open throttle. So the effect of this is that we drop back here and this changes our fuelling delivery. Now whether or not that's going to be accurate though is a little bit dependent on how much specifically our altitude is changing, how much our barometric pressure is changing.
So again this comes down to what sort of changes in altitude you are personally likely to experience so if you are driving, tuning, at a relatively fixed altitude and your likely altitude changes are only going to be in the vicinity of maybe less than 1000 ft, then dealing with barometric air pressure change is probably not a big consideration. So how I tend to suggest dealing with this is using a wideband controller or a wideband input to the ECU and using the closed loop control to allow the fuelling to just change in the background to account for any barometric air pressure changes because any changes should be relatively small. So generally you're probably going to be fine with allowing at wide open throttle, maybe somewhere in the vicinity of plus or minus 5% trim for your fulling. Because again, your changes will be small. Now of course, that doesn't take into account any changes in our ignition timing.
However with the ignition timing we also know that in general if we look at a spark sweep test where we hold the engine at a fixed load and RPM point and we advance the timing from very low timing through to very high timing, we sort of end up getting our torque optimisation curve and we do tend to see quite a wide plateau across the top of that curve where essentially we don't see much change in our torque so again, over a relatively small change in barometric pressure, we're not probably going to need to start diving into making changes to our ignition timing. So that's a solution that's going to be more than workable for probably 95% of people out there who aren't experiencing really dramatic changes in barometric air pressure. However if there are going to be changes in the barometric air pressure, you're living at Pike's Peak for example then we need to think a little bit more about this. We can still choose to use closed loop fuel control and on the Pike's Peak car that I tuned, running a MoTeC M150 ECU, where I'm really confident with the way the closed loop control works on that ECU, that's exactly what I did but I did also build in some background functionality to take care of that so let's have a quick look at the MoTeC M1 software and see how that's done. Actually that's the wrong map but that's OK, let me just load up the one that I did want.
Firmware will do it. And I think yeah here we go. Alright so the MoTeC ECU is a volumetric efficiency based ECU so this table that we see here is a VE table and we've got the table represented graphically over to the right hand side so basically this table is defining to the ECU how much, how efficiently the engine is able to fill its cylinders with air. So again volumetric efficiency though, we're not taking into account there directly in this table, air density changes. So we've got that table tuned and the MoTeC M1 system allows us to add a fourth dimension to the axes for our VE tables.
So we'll bring this up, we'll press A, so we've got our normal parameters, we've got engine speed, pretty typical, we've got our inlet manifold pressure so this is how most ECUs would be set up. With the M1 ECU we have the ability to also add a fourth axis which is our ambient pressure so ambient pressure, barometric air pressure, same thing. So that's being measured by a independent barometric air pressure sensor. Can be done in some ECUs where at key on, it'll use the MAP sensor to lock in a barometric air pressure reading which is fine if you aren't then expecting to see dramatic altitude changes. So that's sort of a way a lot of ECUs get around using a barometric, not needing a barometric air pressure sensor, they just take the reading from the MAP sensor before the engine is started.
So I've got this set up really simple here with three load points, we've got 110 kPa, so that's slightly above, or 10 kPa above standard sea level. We've got 90 kPa and then we've got 60 kPa. So I actually set this up based on logging from our testing at Pike's Peak. We have three test days where we test at the lower section, the middle section and the upper section of the mountain. So got the ability to get quite a bit of data and was looking essentially at what the closed loop trims were doing.
I knew that at the start line we were around about 85 to maybe 90 kPa, I think we were a little bit lower than that but yeah in that vicinity and then as I mentioned, probably around about 63, 65 kPa at the top. So basically those load points span that. And then what we can do is basically copy and paste our volumetric efficiency table to each of those points. So in my mind, this is kind of a round about way of dealing with the issue and it's not really in my opinion maybe the nicest way but it does work. And the ECU simply interpolates just like everything else between these different barometric air pressure points on the axis.
So that's one way of dealing with it. The other way that I'll just mention here and we'll jump across to our Link G4+ software for a second. And this is how our Nissan 350z was set up. So Link include an option for a load axis on the fuel table which we can see here which is MGP which stands for manifold gauge pressure. So essentially what it's doing is it's defining the difference between our manifold pressure and our barometric air pressure.
So the idea here is that this is supposed to deal with changes in barometric air pressure. There's some arguments for and some arguments against but I think when all things are considered, it doesn't actually do the best job possible of this. It's not too bad at wide open throttle on a naturally aspirated engine if you are assuming that the exhaust pressure is the same as barometric air pressure, but particularly on a turbocharged engine, it doesn't do a great job and at very high manifold vacuum, even on a naturally aspirated engine it doesn't do a very good job. So the idea here is that this load point here, 0 MGP, this is where our manifold pressure and our barometric air pressure are the same. So the point with this is that with the ECU tables set up like this, we find that, let's say we're at 3000 RPM, 0 kPa on our MGP scale and we can see that our volumetric efficiency at that particular cell is 116%, maybe not very believable but that's a question for another day.
So that's at sea level so our manifold pressure and our barometric air pressure are both let's say 101.3 kPa. So let's say we then climb up to the top of Pike's Peak and our barometric air pressure is now 65 kPa, but in this case at wide open throttle, forgetting for a moment about any inlet restrictions, we've still got 65 kPa of manifold pressure at wide open throttle. So because our manifold pressure and our barometric air pressure are the same, we actually still stay in the same point on that table. So this has the effect obviously on the final amount of fuelling that's going to be used. There is also a background compensation here that's important to mention that takes into account the actual manifold pressure so that manifold pressure of 65 kPa still goes into the fuel calculation that defines the final amount of fuel that will be delivered.
So as I've mentioned, manifold gauge pressure, doesn't do a bad job in a naturally aspirated engine at wide open throttle but it's still not the ideal way of modelling this. And the reason for this is what we really want to know is the pressure ratio across the engine so we can't think of the airflow through the engine just by considering what's happening in the inlet manifold. What we actually need to understand as well is what's happening in the exhaust side. So as I mentioned, when we're, particularly when we're dealing with turbocharged engines, if we are trying to maintain a fixed manifold pressure with our boost as altitude changes, we're going to be driving that turbocharger harder and harder and what that's going to do is mean that our inlet manifold pressure will stay the same but as altitude climbs, our exhaust back pressure is going to climb. So obviously, if you can understand that it's going to mean that even though we have a fixed or consistent manifold pressure, that doesn't mean that the volumetric efficiency of the engine is going to stay the same.
As altitude increases and our barometric air pressure drops, the turbo needs to work harder, exhaust back pressure rises so the pressure ratio across the engine drops and reduces. I know this is a lot to take in, don't worry we're going to. have a look at how that works out in just a second. So on this basis, really if we want to do things the best way possible, what we want to really do is look at that pressure ratio as our load axis. And this does get a little bit tricky because in order to do this, we need to have a exhaust back pressure sensor fitted to the engine and in its own right that can be a little bit tricky, we need to plumb that in, we need to protect the sensor from heat and we also need to dampen out the inevitable pulsations that we're going to see from that exhaust back pressure because you can understand that the pressure is spiking as a result of the opening and closing exhaust valves so that raw signal tends to be quite messy and it's not something that's immediately suitable for use in a load calculation.
But it can be done, there's various exhaust back pressure dampers on the market from the likes of T1 Race we've got on one of our cars, Full Function Engineering I think, or full form engineering as well, we've got on our FD RX-7 and basically they do a good job of just getting rid of those pressure pulsations. So I'll show you what we've got here, back into our tuning software here in the MoTeC and I've actually done this in M1 build so I've written some custom firmware for our Toyota 86 just to experiment with how this looks. So what we've got here on our fuel table is our engine load normalised, that's what they call the axes but essentially the numbers here are our pressure ratio. So all we're doing is we're taking the inlet manifold pressure and we're dividing it by the exhaust manifold pressure and that defines where abouts we are running on this particular table. Now the advantage with this is that when it's properly calibrated it's going to automatically compensate for changes in barometric air pressure because it defines, the barometric air pressure will affect our pressure ratio which then defines of course where we're operating in this table.
So if we just get rid of that for a moment. What we tend to find, and you can sort of see where abouts we're operating through this, we start at about 1500 RPM here with a pressure ratio of about 1.1. Basically we've got no exhaust back pressure, that's barometric at this point, we've just got slightly positive air pressure in the inlet manifold. As the manifold pressure climbs we see we move up through this table and then as the exhaust manifold pressure starts to increase, we drop away. So our inlet manifold pressure stays the same but the barometric air pressure increases, the exhaust back pressure increases so we start to see we taper off and I probably should have been in a different spot there, we sort of peak at around about 1.3, 1.4 in this table and then by about 7000 RPM we're all the way back down to about 0.9 because the exhaust back pressure has just exceeded the inlet pressure.
So it's a nice way of doing it if you can get those inputs into the ECU. What I do find from a tuning perspective is it's a little less intuitive to understand exactly where about you're operating inside of this table so that is one consideration. You need to be a little bit more mindful because it's not just a case of looking at a log file and seeing oh yeah I was at 200 kPa, 7000 RPM. You need to make sure that you're actually taking note of the pressure ratio, not just your manifold pressure. In this particular example, if we jump across to the ignition table, I am still just using a conventional manifold absolute pressure for the load axis so that's not really accounting for the exhaust manifold back pressure.
It would be possible, if you want to get really messy with your tuning to also use pressure ratio for your ignition table but in this case I haven't seen fit to do that. Now if we jump back into our Haltech software as well for a moment, there are quite a few ECUs on the market that actually allow this as a load axis anyway so if we go across to our fuel under our settings we can see we've got our fuel load type. And at the moment it's on MAP sensor which again would be the most conventional. If we open that up we can see that we have air mass per cylinder, we've got throttle position sensor or engine pressure ratio so the Haltech by default allows that particular load axis. Adaptronic is another one that springs to mind that also allows the pressure ratio as a load axis as well.
Alright so that's one option, again it's not a particularly common one but it is good to understand that short of using a mass airflow sensor this is probably the most accurate way of accomodating large changes in barometric air pressure. The other way we can do this though in an ECU that doesn't provide this option, It's a little bit more work but we can set up barometric air pressure as an auxiliary sensor input into the ECU and then we can use a three dimensional compensation table for fuel and ignition and boost pressure if we want. So we're going to jump into our questions and answers really really shortly, I see we've got a couple of questions in there and this is a good time to just say if you've got any more questions, please feel free to keep asking those. So just to get back to using the barometric air pressure correction, 3D compensation table if that's the way you want to go, so how do we go about getting this set up? A question I get is can we do this from theory or is there another way of doing it? The answer in my opinion or my experience I should say is that you are best to simply do this by logging to find out exactly what is happening to your fuelling at different barometric air pressure points and then use that data from your logging to fill in that table. That's going to give you the best, most reliable results and essentially that's what I did with the MoTeC M1 in the Pike's Peak hill climb car.
We ha all of that log data and that allowed me to fill in the VE tables at the four different barometric air pressure points. And as I've mentioned, you can then use that same compensation, once you've got barometric air pressure into the ECU, depending on your ECU you can compensate for your boost targets as well as your ignition timing if required. Alright let's see what we've got in here in our questions. Manitou Black's asked, can't you just use closed loop boost control to target specific manifold pressure, that way the wastegate controller sorts it out for you to keep the performance constant as the altitude changes? Yes you can but that sort of overlooks the fact that you still need to take into account turbo performance. So yes if you are going to maintain a fixed manifold pressure.
And that was essentially what I was doing with the Pike's Peak hill climb car. We still need to take into account the pressure ratio that the turbo is working at because to maintain that same fixed manifold pressure as we climb up in altitude, we're pushing that turbo harder and harder, the turbo's working at a higher pressure ratio. And particularly one thing we see at Pike's Peak is a lot of the cars that are developed for competition, and they're optimised around a sea level configuration, when they get to the altitude of Pike's Peak they're already at or potentially beyond the maximum turbo speed limit so obviously if you're going to be pushing the turbo to that point, you can expect a failure. So the other thing to keep in mind there is again this gets a little bit deeper than a lot of people sort of initially think. Manifold pressure on its own is only part of the situation we need to consider.
It's also that back pressure so again it's the pressure ratio across the engine that defines what we need to do with our fuelling and ignition timing, defines the volumetric efficiency of the engine so again with our fixed manifold pressure, that's great, we're holding that at the same point but as our altitude increases and we have to drive the turbo harder and harder, our exhaust manifold pressure increases so even with that fixed manifold pressure, even if our turbo efficiency, our compressor efficiency didn't change which it definitely will be, we're still going to find that our volumetric efficiency of our engine drops away and we need to reduce our fuelling in order to maintan a fixed air/fuel ratio. Barry's asked, for turbocharged engines can we achieve the same type of barometric compensation by fitting a MAP sensor to the inlet of the turbo? No, so that's going to give us the pressure at the turbo inlet which is great. Unless your intake system is incredibly restrictive we'd hope that that should be at or very very close to barometric air pressure. If it isn't, that means that your turbo inlet system is restricted. But it still doesn't change the fact that we aren't compensating for the increasing exhaust back pressure.
So basically what you're doing there is you are just fitting a barometric air pressure sensor, you are going to be able to get a very accurate picture of the exact pressure ratio you're operating the turbo at but again no compensation for that increasing exhaust back pressure. So when I talked about using a 3D compensation table for barometric air pressure in an ECU that doesn't have another way of dealing with it, what we're kind of doing is baking into that compensation table the effect of that rising exhaust back pressure so it's not a direct way of dealing with it but it does work if you can understand that. Sheldon's asked, when setting up baro correction on a Haltech Elite in TPS based VE mode, does this ECU to the auto baro correction in the background like it does VE air temp correction or does the baro correction table also need to be enabled? No if you want full barometric air pressure correction, regardless whether you're using TPS or MAP for your load axis in your VE table, you still do need to enable and tune the barometric correction table. Manitou Black's asked, will you be using both IMAP and EMAP in the M6000 in the FD RX-7 and tuning in pressure ratio? We are certainly going to try that which is why we've gone to not inconsiderable trouble to fit two exhaust manifold back pressure sensors, one to each exhaust runner on the manifold. So the Adaptronic as I mentioned is one of the few ECUs that I've seen that do natively allow for IMAP over EMAP as a load axis.
So yeah really interested to see how that works out. Again given our situation here in Queenstown with a relatively small altitude change, it's not going to be essential but we're going to be doing this for course production and webinar content as much as our own learning and investigation as well. Alright that's all the questions we've got there so thanks to everyone who has joined us. Remember if you are watching this in our archive at a later point if you've got further questions, please ask those in the forum and I'll be happy to answer them there. Thanks everyone who's joined us today and hopefully everyone learned a little bit more about altitude and tuning, cheers.