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Practical Standalone Tuning: Considerations

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Considerations

12.22

00:00 - Before we get started with the tuning process, I'm just going to take a moment to discuss some of the considerations we need to make with a turbo charged engine, or in other words, what differences we can expect a turbo charged engine to exhibit in comparison to a naturally aspirated engine.
00:17 And first of all, we need to consider what's going to be happening as we move into positive boost pressure with a turbo charged engine.
00:25 And essentially, when we move into positive boost pressure, what we're doing is forcing more air into the combustion chamber.
00:33 And this is really how a turbo charged engine can produce more power than a naturally aspirated one.
00:38 Now, of course, as we force more air into the combustion chamber, we need to match this with more fuel.
00:45 However, as we are combusting more air and more fuel, we find that the heat inside the combustion chamber is going to become a lot higher than what we could expect with a naturally aspirated engine.
00:57 So one of the considerations with a turbo charged engine is that as we move into positive boost pressure, we're going to need to start targeting a richer air fuel ratio than what we would use with a naturally aspirated engine in order to manage that additional heat.
01:14 So this is why we see a richer air fuel ratio being used with a turbo charged engine.
01:20 Now, we're not going to be discussing air fuel ratio in detail in this section of the course.
01:26 If you need a more thorough understanding of this and how to choose the correct air fuel ratio for you particular engine, I'd recommend our understanding air fuel ratio course.
01:37 Now, let's just have a look at what our air fuel ratio target map looks like.
01:43 So for this particular example, we're going to be using our Toyota 86 fitted with a turbo charger and our MoTeC M150 ECU.
01:52 Of course, it's the concepts that are important during this section of the course.
01:56 And this will relate to any turbo charged engine and any ECU.
02:01 So here we have our fuel mixture aim table.
02:04 This is the target air fuel ratios that we want the engine to be running.
02:08 And you can see that we have our inlet manifold pressure on the vertical axis, and of course we've got our engine RPM on the horizontal axis.
02:17 To the right, you can see that we have a graphical representation of the numbers in our air fuel ratio mixture aim table.
02:26 And what you can see here is that in the idle and cruise areas I have lambda one point zero as my target.
02:34 For a naturally aspirated engine, we'd find that the hundred KPA row, which I just highlighted here, this is going to be our maximum load area.
02:45 This is the maximum amount of load we can place on the engine.
02:48 However, with a turbo charged engine, obviously, we can now move up into these positive boost areas.
02:55 So you can see that as we transition from vacuum up into the positive boost areas, we're seeing that air fuel ratio target or lambda target consistently move richer.
03:08 So this again is to combat the additional heat involved with a turbo charged engine.
03:15 The other aspect that we do need to consider with a turbo charged engine that is that as we combust more air and more fuel inside the combustion chamber we're going to find that we need to retard the ignition timing.
03:30 And there's two reasons for this.
03:31 First of all, when we are combusting more air and fuel we find that the fuel and air molecules are much more tightly packed together.
03:39 This results in the actual combustion event occurring faster than if we had less air and fuel in our cylinder as we might expect to see with a naturally aspirated engine.
03:50 This means that in order to reach MBT timing, we actually don't need as much ignition advance as if we were combusting less fuel and air.
04:00 So a general trend that we see is that as we move further into positive boost pressure we're going to see our ignition timing retard.
04:09 Let's just jump across to our ignition table, and if we view this graphically, we'll be able to see the sort of shape we might expect from our ignition table.
04:19 Again, we've got our engine load on our vertical axis.
04:24 And we have engine RPM on our horizontal axis.
04:28 And if we move a little bit across in the table to a position where we're actually operating in boost, let's say, in this case, 5000 RPM, you can see that, that this point, at 100 KPA we have 22 degrees of ignition advance, whereas if we move up to the positive boost pressure area at 170 KPA, so this is 70 KPA or round about 10 PSI of positive boost pressure, you can see the ignition timing has now been retarded back to fourteen degrees.
04:59 So this is what we're expecting to see with our ignition timing.
05:04 Now the other consideration we need to make, with a turbo charged engine, is the way that the engine is going to run while it's on the dyno.
05:13 Now again, because we're producing more power from a turbo charged engine in comparison to a naturally aspirated engine, managing the heat on the dyno is a big consideration for the tuner.
05:26 This comes down to two main areas.
05:29 We're going to want to monitor our engine coolant temperature.
05:32 It's very easy particularly when we're tuning in steady state to find the engine coolant temperature start to climb rapidly.
05:40 So we really want to monitor that carefully and make sure our engine isn't overheating while we're tuning.
05:47 It's very easy to get so carried away with the actual tuning process, regardless if we're tuning fuel or ignition, watching our dyno and making changes to the number in the fuel and ignition tables that we forget to watch the engine coolant temp and that can be a dangerous scenario.
06:04 So we know our engine is likely to gain temperature much quicker than a naturally aspirated engine.
06:11 The other consideration that's important is our inlet air temperature.
06:15 Now, when we compress air naturally it will be heated.
06:19 So the air being compressed by our turbo charger is going to be a lot hotter than what we'd likely see with a naturally aspirated engine.
06:29 The more boost we're running, the worst the scenario becomes Now, of course, most turbo engines will be fitted with an intercooler.
06:37 And the intercooler's task is to reduce that heat, get rid of some of that heat out of our inlet air.
06:44 But if we're tuning in steady state, and we're constantly sitting in positive boost pressure, it's likely that our intercooler may become heat soaked and what we're going to see in that case is our inlet air temperature may start to climb quite rapidly.
06:58 When we're tuning, we always want to make sure we're tuning with realistic values for our intake air temperature and our engine coolant temperature.
07:06 And by realistic, I mean the sort of temperatures we're likely to see out on the road or the racetrack.
07:12 If we do this and we're tuning with the same temperatures we see on the road or track, it's going to mean our tuning is much more precise, much more accurate, and we should see the same results when we are out in the real world.
07:25 So of course, on the dyno it's very hard to replicate the air flow we'll see at speed out on the road or track.
07:31 And this is why we're likely to see more heat soak occurring than when we're actually out, off the dyno, in the real world.
07:37 So we need to monitor both of those parameters.
07:40 Now, how we do this is going to depend on the particular software you're using.
07:45 My recommendation would be to make a mental note to always check the engine coolant temperature and intake air temperature after every change you've made to a cell, regardless if that's fuel or ignition.
07:58 Let's have a quick look at a function that is in the MoTeC M1 ECU I am using.
08:03 And if we click on the alarms, you can see I've got three alarms set up.
08:07 Now this means that if any of the parameters I've got alarms set up for go outside an area I'm comfortable with, I'm going to get a visual warning pop up on my tuning software.
08:17 This means I don't have to be concentrating on our engine coolant temp or our intake air temp.
08:23 In this case, I've also set up a warning for engine oil temperature.
08:27 So you can see, just looking at one of these here, I've got a warning for coolant temperature, and if the coolant temperature exceeds a hundred degrees centigrade, this is going to bring up a warning to visually indicate that I've got a problem with the coolant temperature.
08:42 I can stop what I'm doing, stop my tuning, and allow the coolant temperature to come back down to a temperature I'm more comfortable with.
08:50 So how you choose to do this, is to say, will depend on your software.
08:53 It is something that you do need to keep in mind.
08:57 Now that we've got a better idea of some of the considerations we need to make when we're tuning a turbo charged engine, it's going to be useful if we know whereabouts the engine's likely to be operating so we can focus our tuning efforts in the area the engine's most often going to be accessing.
09:14 So let's have a look at an air fuel ratio target map.
09:17 And what I've got here is an air fuel ratio target map with load on our vertical axis and KPA.
09:24 So the hundred KPAs are what you can see here.
09:27 This represents atmospheric pressure.
09:29 Now, I've just drawn a red line here that demonstrates a likely boost curve that we might expect to see if we did a ramp run on a turbo charged engine.
09:40 So you can see that at a thousand RPM we're not seeing any positive boost pressure.
09:45 As we move through the rev range, we can see that the boost pressure starts to climb quite rapidly.
09:50 And in this case, my little example here, we've got the boost sitting just under 200 KPA, so just below one bar of positive boost pressure, so approximately almost 15 PSI of boost pressure.
10:02 So we need to understand where the engine is going to spend most of its time operating.
10:08 And you can see we have our cruise area highlighted at the bottom of our AFR target map.
10:14 For a naturally aspirated engine, this is the area we're going to be spending most of our time.
10:20 And the same could even be said for a turbo charged engine.
10:23 However, this time with a turbo charged engine we're actually going to extend the area that we're going to be interested in.
10:30 So we're going to be looking at our cruise area, but we're also going to be able to quite easily see the engine run at moderate boost pressure at low RPMs.
10:40 So here I'm focusing between 2000 and about 4500 RPM.
10:45 And you can see that we're accessing the areas of high vacuum so this is where we're completely off the throttle.
10:52 But this time, we're also extending this up to partial boost pressure.
10:56 This is because if we're operating at relatively low RPM and we use a little bit of throttle to accelerate the turbo charged engine, we're quite likely to see the engine move into relatively low boost pressure quite easily.
11:11 Likewise, we'll also see the engine running low boost pressure if we're climbing a hill, using a little bit of throttle to maintain consistent speed.
11:21 So unlike a naturally aspirated engine, we're quite likely to see the cruise area extend out into the low boost area.
11:29 And this is where we want to focus our energies when we move on a little bit later and start looking at the steady state tuning process, rather than just focusing on the tuning up to 100 KPA as we saw with a naturally aspirated engine, we're now going to extend our tuning process for steady state up into the positive boost pressure areas.
11:51 And really the key to this is all about understanding how the engine is going to be used, where it's likely to be operating in terms of load and RPM, and addressing these the most accurate way we possibly can when we're tuning on the dyno, and this his how we're going to be using both our steady state and our full power ramp run tuning processes.