174 | Configuring Rolling Launch Control (Antilag)
If you’re running a turbocharged car in roll-racing events, rolling launch control is an essential requirement to build boost while maintaining a constant speed, allowing for fast and consistent launches. In this webinar we’ll look at generic rolling launch control systems, see how they are configured, and see the results on our Toyota 86 running a MoTeC M150 ECU.
- Hey guys it's Andre from High Performance Academy, welcome along to another webinar where today we're going to be investigating rolling launch control, or rolling anti lag as it may also be known. Today we are gonna be demonstrating this using our Toyota 86 which has been fitted with a turbocharger, it's running a custom Motec M150 firmware setup. So a lot of this isn't going to necessarily translate directly across to Motec's production firmware. And it's definitely not the best car for demonstrating this on. Generally when we're using rolling launch control, we're going to be using this on a much more powerful engine running large turbochargers, running high boost pressures which can be very very laggy, on a small displacement engine.
So the whole premise behind rolling launch control is to try and build boost while the car is driving at a fixed speed. So that when the driver wants to start a roll race event, the engine is already at full boost, making good power and it can get the best possible start. So here with our Toyota 86 we're going to be able to demonstrate the principles behind this but we've got a really small turbocharger on an otherwise stock naturally aspirated engine. We don't run very much boost on it, and lag certainly isn't a problem. However again it's the principles that we're going to be talking about here, so a lot of this should be still applicable to a wider range of ECUs.
So the first step is why do we need, or the first aspect to talk about is why do we need rolling launch control, and I've sort of touched on a few of the aspects there. One of them is that when we want to make a lot of power with a small displacement engine, really what we're going to often be doing is fitting large turbochargers. Now large turbochargers work exceptionally well when we are high up in the rev range, where we already have those turbochargers up on full boost, and this produces a lot of air flow at high RPM which is ideal when we wanna make high power levels. The problem with these large turbochargers particularly when they are mated with a small displacement engine, is it can be very difficult to actually build boost at low RPM. So once the engine's actually up on the boil and the turbochargers are spooling, everything's fine, but it's a case of getting it there in the first place, and this is where our rolling launch control strategy comes in, what we're doing is essentially adapting the technique that's already used on turbocharged drag race cars, to achieve exactly the same aim.
Only we now wanna achieve this when we are driving the car at a fixed speed. So we'll talk now about how the rolling launch control strategy works. So in order to do this, what I'm going to do is show you a little bit of data from one of the cars that we were involved with a number of years ago. So I've just managed to delete this off my screen, no I haven't, just bear with me while I actually find it, here we go. Let's jump across to my laptop screen and I'll just talk you briefly through the car that we're going to be looking at the data from.
So this was a Mitsubishi Evo 9 that we built for a customer a number of years ago now. And at the time it was retired, it held the world record for the fastest Mitsubishi Evo four wheel drive, late model Evo four wheel drive. And it held that record with an 8.34 at 169.7 mile an hour. Now it's based on the Mitsubishi 4G63 although we did add a little bit more capacity using a 2.2 litre stroker kit. The reason I wanted to show you the engine bay though is the problem with getting fast launches from a drag car like this, is all to do with this massive turbocharger that we have fitted.
Now technology has moved on a long way since we built this car. I certainly wouldn't be picking this particular turbocharger right now, if we were to rebuild this combination, but we used a Garrett GT4202 turbocharger was mated to a Teal exhaust housing, stainless steel v band exhaust housing. And the combination was good for producing around about 1001 wheel horsepower running 42 psi of boost on our Dynopack four wheel drive chassis dyno. Now if we simply did a full power run on that chassis dyno from 2000 or 3000 RPM through to the 10500 RPM rev limit, we weren't going to see full boost from that combination until around about 7000, 7500 RPM. So this is the compromise we get, this is the price we pay when we are fitting a very large turbocharger.
That very large turbocharger needs a large amount of exhaust gas energy in order to spool it up, and actually start producing speed in the compressor and turbine assembly which in turn produces boost pressure. So they're not very well matched to a small displacement, four cylinder engine. Now what I wanted to show you is the technique that we use for getting this turbocharger to produce good boost when we are at the start of a standing quarter mile drag race. So again we'll head across to my laptop screen. So this is some data actually from the car's fastest run from its world record 8.34 169.7 mile an hour run.
And this is in Motec's I2 so this is actually set up as a drag race run. So what we can see here is there are some vertical lines through this data which represent the point where the car actually first crossed the beams, the 60 foot, 330, 660, et cetera. That's not too important, we're not really looking at the data in terms of a drag race here, what we wanna do is look at what we're doing inside the ECU to actually produce boost very very quickly while the car is stationary. So first of all at the top here, we have our engine RPM, that's our red line here. And this is the point where the driver has first gone to full throttle, and we can see that the engine RPM is held at about 7300 RPM.
So I'll just draw a line through this, so we can see we've got our engine RPM sitting stationary. The third graph down here is our throttle position. So that's the green trace we can see. So we can see that the driver has gone to full throttle. And our middle trace here in blue is our manifold pressure.
So this is our boost pressure being measured in kPa. So you can see that initially as soon as the driver goes through to full throttle, that's about where he's got to that there, and we come up, the engine RPM is still rising. We come up to about 6000 RPM and you can see we've only got 120 kPa there of manifold pressure. Now this is absolute, so 100 kPa is atmospheric pressure, this means we've only got 20 kPa of positive boost pressure. So for those who like to work in psi, around about three psi of boost pressure or a little bit less.
So absolutely nothing. Now if we had continued to just sit on a rev limiter there at 7300 RPM and full throttle, we probably wouldn't have ended up with a huge amount more boost than that, we might've settled at maybe five to 10 psi of boost, maybe a little bit less than that actually but certainly not enough to actually get the car to launch. So what we employ here is a launch control strategy where we retard the ignition timing quite dramatically. So our last group that's visible here is our ignition advance and that's what we can see in red. Now we can see that when the driver goes to full throttle, initially with our 120 kPa of inlet manifold pressure, we've got around about 6.8, seven degrees of ignition advance.
The white reference line that we have in this graph here is zero degrees of ignition advance. And what we can see is that our ignition advance actually retards. So it's occurring after top dead centre. So this is the key point. What we're doing is using a rev limiter that consists of an ignition cut limit, so the ECU is randomly cutting spark to individual cylinders in order to maintain our fixed launch rev limit of 7300 RPM.
So in conjunction with this, what we're ending up doing is the ECU is passing, or the engine is passing, cylinders full of unburned fuel and air out into the exhaust manifold and this is one of the key aspects of the rolling launch control strategy, or any launch control strategy with a turbocharged car. A combination of that combined with also massively retarding the ignition timing, so at its peak here, we can see our ignition timing's retarded to 8.5 degrees after TDC. What this does is it continues the combustion process on the cylinders where the spark is still present, far later into the engine cycle, and this has the benefit of then creating a burn that continues with the unburned fuel and air passing through into the exhaust manifold. This provides energy directly to the turbocharger. So it's sort of like a rally style anti lag, only this time it's happening when the driver is at wide open throttle.
So we can see that we end up with the driver reaching around about 220, to 240 kPa. So around about 1.4 bar, around about 20 psi of positive boost pressure, which for this combination is about the amount of boost pressure that we could maintain or could actually launch the car and get a really good standing start from. Now what we can see though as well, is that once the boost actually comes up and stabilises, it does move around a little bit in this point. But it is relatively stable and what we're actually doing here, hopefully you can see here, we're actually manipulating now both the boost control, which you can't see in these graphs, as well as the ignition advance or retard in order to control the boost pressure. So if we continue to use a large amount of ignition retard, what we're ending up doing is providing more and more energy to the turbocharger to help spool it.
And this will continue with the boost pressure climbing. Obviously that's not what we want to do. So once we get to the boost pressure we want, we start adding timing back in. So we reduce the amount of retard that the ECU is applying, and by manipulating these parameters, we can quite accurately control the amount of boost pressure we've got. And of course for anyone wanting to get fast and consistent standing starts, it really is an essential aspect to make sure that you control the amount of power that the engine has on the line.
Alright so what we'll do now is we're going to jump across and I'm going to take you through the way I've configured the rolling launch control strategy in our Toyota 86. And just to reiterate really for our 86, this is not necessary. Obviously it doesn't have a lot of power, it is a stock engine, and we're certainly not entering this in any roll race events. I'm not expecting it to take down any 2500 horsepower Nissan GT-Rs any time in the foreseeable future. This is really just a case of developing the firmware to see what we could make it do and how well or how effective it was.
So at the moment we're looking at all of the rolling launch control parameters that we have available and again this may vary depending on exactly what system you're using. But the key point here is that the fundamentals or the principal behind it will remain the same. What we're going to obviously need is some way of telling the ECU that we want to enter a launch control strategy. And in this case with our Toyota 86, we're actually doing this via the cruise control stalk and that is a CAN message that is being sent to the ECU. So basically once we're within our launch control strategy parameters, and everything is ready to go, we can signal the ECU to engage the rolling launch control by simply holding down on our cruise control stalk.
So we'll go through these parameters here. At the moment we've got the engine just sitting at idle so we'll have a look at this in a little bit more detail shortly. So here we've got our mode. So this is a master enable or disable for the system. So we've got it overall enabled.
The next parameter down we have our throttle position threshold. So this is just a safeguard to make sure that the launch control strategy isn't engaged accidentally. So in this case the throttle position needs to be below this parameter, in this case I've got it set to 40% in order for the ECU to engage launch control in the first place. Likewise we have a coolant temperature threshold here which I've got set to 60 degrees so this just helps prevent the launch control strategy from being engaged when the engine is too cold. So in this case won't engage until we are over 60 degrees centigrade.
Likewise we've also got a vehicle speed threshold. So this means that the vehicle speed must be above this point in order for the launch control strategy to be enabled. I've got that set to zero which essentially disables it. Now a novel strategy that I've added into this as well and I've seen quite a lot of roll race video where one competitor will end up engaging rolling launch control at a different speed to the other and traditionally this is pretty difficult to fix, once the system is engaged that's basically it. So what I've actually done here is I've also included an engine speed bump parameter.
So this can be set so that every time we press the up button on our cruise control, it will add in this case, 100 RPM to the launch control set point. So this just allows us to help match the speed with the competitor in the other lane. Obviously of course here, if we are using this launch control strategy for a roll race event. The next aspect down here we've got our boost aim. So when the launch control strategy is engaged, the Motec ECU will actually use a completely separate boost aim target.
So in this case we're looking for a whopping 40 kPa of positive boost pressure, and the M1 ECU working in gauge pressure so certainly not a lot of boost pressure. Again just remembering that we are running a naturally aspirated engine with a turbocharger so we do need to be a little bit mindful there. Lastly we have our ignition retard. And this is really the key to the launch control strategy. So this is a two dimensional table, we can see this over here on the right hand side.
So we've got our inlet manifold pressure as one axis. And then we've got the ignition retard on the other axis. So what we can do here is retard the timing to achieve our boost target aim. So we can see here, and again I'm being reasonably conservative with this engine, once we get to 100 kPa here which is atmospheric pressure, you can see that we start retarding the timing by 18 degrees. As we get to 125 kPa and build a little bit more boost, we're still retarding 18 degrees.
As we get to 150 kPa, remember this is above our target boost of 40 kPa gauge, we're starting to add some of that timing back in so the ignition retard is actually reduced and we can manipulate this table to suit. Now I'm gonna show you some data really shortly, but I also just wanted to show you one of the novel aspects of this setup. So what I'll do is I'll just get us up and running, let's hope that's working. And I just wanted to have a really clear indication to the driver of what was going on. So when we use the cruise control to engage the rolling launch control, we also send some date to the Motec dash via CAN.
So we can see that we've got our shift light module flashing there to tell the driver that the launch control is armed and we've obviously got that message also saying that the launch is armed. Now when we want to disarm our launch control, we can simply press it again and it's instantly deactivated and we're back to our normal engine RPM limit. So as soon as we press that cruise control stalk again, that deactivates it. So the idea with this system, is what we'll do is we'll get into the gear that we want to launch in, we'll get to whatever RPM or speed that we are going to be locking our launch control in, and then we're going to hold down on that cruise control stalk, and that will put the ECU into our rolling launch control mode. And it will hold the engine RPM at whatever RPM we were at at the point we enable the system.
From here though we can of course use that bump function that I talked about in order to match the speed of the car that's in the other lane. From there when we're ready to go, we can go straight to full throttle. That will also bring in our ignition retard, it will bring in our secondary boost target and we should, if we've got the system tuned correctly, achieve whatever we're trying for. As soon as we get the green light, the flag, whatever initiates the launch, we can disable the launch control, we're already at full throttle, the engine's already got full boost, and we're away. Now I just wanted to go through some data from this system.
Now again just understanding that unfortunately our Toyota 86 is really not a great example for demonstrating this system. So you're just gonna have to use your imagination a little bit here, and look at the data that I'm displaying. So again on my laptop screen, we've got a few graphs set up here. In the top graph we've got our engine speed. Then we've got throttle position, we've got our inlet manifold pressure in purple along with our exhaust manifold pressure in orange, just so you can see what's happening to the exhaust manifold back pressure.
And then we've got our ignition timing. So I've got two tests here that I ran just before we started this webinar. In both tests we've locked the launch control strategy at 4500 RPM give or take. So we can see that's exactly where we are here, and you can see that we've gone through to full throttle. Now in this first test we are using no ignition retard.
So this is just the normal ignition table values from our ignition table with no manipulation. So you can see we're sitting around about 23 degrees of ignition advance. And that's given us a pretty uninspiring 22 kPa of positive boost pressure. So nothing to write home about there. We can see our exhaust manifold pressure sitting just slightly above atmospheric, around 108 kPa.
So basically what this means is that for that sort of RPM, we're only able to generate, for this test, about 20 kPa of positive boost pressure. So to see what happens when we now use a little bit of ignition retard, let's just bring our data over here, we've performed exactly the same test again. So 4500 RPM still, 100% throttle still. This time though you can see that I've retarded the timing. You'll remember that we started with 23 degrees ignition advance.
You can see this time for our second test we've got three degrees of ignition advance. So we've retarded the timing somewhere in the region of about 20 degrees there. It's actually a little bit less because we've also got more boost. Now the result of this is two fold. Because we've got both of the pieces of data, we can see really clearly what's happening.
We can see the orange graph here, our exhaust manifold pressure, you can see the sharp spikes in the pressure as a result of the combustion that's now occurring in the exhaust manifold. So we've got a lot more pressure, we're peaking at around about 135 kPa compared to the 108 kPa we had previously. And the result of this as well is while our boost is spiking around a little bit, we're sitting at around about 140 to 150 kPa. So again bear in mind this isn't the best demonstration. If we were genuinely running a larger turbo on a small displacement built engine that we could confidently lean on, what I would be using is a lot more RPM, I'd also be using a lot more ignition retard and really aggressively driving the turbocharger to achieve our target boost pressure.
But hopefully this does still demonstrate what we're trying to achieve. Alright we are going to move into some questions and answers really shortly. Before I do that, I just want to go over the tuning strategy that we would use with a rolling launch control. So if you do have any questions, please ask those in the comments. And I'll deal with those shortly.
So in terms of the tuning strategy, again this is going to depend a little bit on the particular ECU you are setting up and how you're actually activating the launch control strategy. Often it's going to start with a digital switch or some way of triggering the ECU and telling it that you are activating the launch control strategy. Often this will also require a latching switch. So essentially we press the switch once, and it latches in the on position. And then when we press the switch a second time, it will deactivate.
So essentially this is what I'm achieving through the cruise control stalk, but there's a number of different ways of achieving that same end result. Now it is important, if you wanna get the best results from this strategy, that we are using an ignition cut rev limiter. It's not gonna work anywhere near as effectively and in some cases it will be completely ineffective if you are using a fuel cut strategy. The reason for this is it really relies on unburned fuel and air being available in the exhaust manifold. This is combusted by way of the massively retarded ignition timing and the combustion process continuing very late in the engine cycle.
So if you are using a fuel cut limiter, while yes this is much gentler on the engine, it isn't going to be anywhere near as effective because you don't have that amount of unburned fuel to promote combustion. So this is where you need to be very very careful. I would suggest, if you are considering setting up a ignition cut rev limiter, that you review our webinar on rev limits. Just search for that in the webinar archive cause there's a lot of information in there about the pros and cons of ignition cut versus fuel cut. The important takeaway here that I'll just touch on though, is that you do need to be very careful because in some engines with known fragile valve trains, one of the ones that jumps to mind straight away here is the Nissan SR20DET.
If you use an ignition cut rev limiter and the valve train isn't significantly beefed up, you may end up running into some pretty expensive engine damage so be aware of that. OK so once you've got your basic strategy set up, what you're going to also want to do is make sure that at least initially you have your wastegate control set to basically make sure the wastegate is completely closed. So this is really important. There's no point driving the engine really hard with a lot of ignition retard to try and meet your boost target, only to find out that a lot of the boost is being bled off or a lot of the exhaust gas energy I should say is being bled off because the wastegate's actually cracking open. So that's something that you do need to watch.
It's really important to actually understand what your wastegate duty cycle is doing. If you do have the benefit of a wastegate position sensor, that can be really helpful, when you are using a lot of ignition retard like this. Because it is creating quite large pressure spikes that are occurring in the exhaust manifold and the exhaust system itself, what you can find is that if you've got quite a soft spring in your wastegate, those pressure spikes alone will be enough to actually pop the wastegate off its seat regardless of what you're actually doing with the boost control strategy. So once you've got that all set up, I also recommend beginning your testing with absolutely no ignition retard. The amount of ignition retard you're going to need is really down to the size of your turbocharger relative to the engine.
And also the sort of RPM range that you're going to be looking at locking your launch control strategy at. So for example if you've got a relatively modest sized turbo on a large capacity engine, you may need little to no ignition retard in order to meet your boost target aims. So that makes everything really nice and easy. In that situation you manipulate and control your boost just through your normal wastegate duty cycle tables. So really when we've got these small capacity engine with massive turbos that we start getting to the situation where no amount of RPM is going to end up getting us the boost we need, so we need to start adding a little bit of ignition retard.
So what we do is begin retarding the timing in perhaps two or three degree increments and just creep up on a point where we start seeing the boost actually jump. And you will also hear this will result in quite a lot of popping and banging from the exhaust system as well. So you're going to know when you start getting to a point where you've got combustion occurring out in the exhaust manifold and out into the turbocharger. So we wanna be really careful with this. I really do suggest that you use the bare minimum amount of ignition retard you need.
It's also a really good idea if you are able to monitor your exhaust gas temperature to do so. By retarding the timing dramatically, it does build a lot of heat in the exhaust system so it's not something that we want to do for a long time. Lastly then we can also look at the strategy of tapering our retard based on our boost targets, that's what I talked about with our two dimensional table in our Motec. We have a retard versus boost pressure table. So as we get up to our boost pressure, we can start reducing our ignition retard, moving back towards our normal table values.
And essentially once the turbocharger is spooled up, it sort of becomes self fulfilling to a degree. So we don't need to maintain those very high levels of retard, we will need those initially to provide energy to the tubrocharger and get it to start spooling, but once we start spooling the turbocharger, it does kind of end up feeding itself to a degree, so we don't need that retard, so we wanna monitor that and be pretty careful. Alright we'll move into some questions now so if you do have any more questions, please ask those in the comments and I'll do my best to answer them. Bob has asked, I have my antilag system triggered through my cruise stalk also, but with the Motec GPR package I don't have the option to latch the car in RPM when the switch is triggered. What do you recommend to do as a work around to make rolling antilag work with the GPR package.
OK so right now this is a little unfair for Motec M1 users because to the best of my knowledge at the moment, there isn't a work around for this. Of course there is a normal launch control strategy in the GPR package but this is designed around a standing start, so a normal drag racing standing start. So at the moment it's not something I can really give you an answer to. I do believe that Motec have been working on a rolling launch control strategy, although that was some time ago, I'm not quite sure exactly where we got to, where Motec got to with that. I'd probably suggest you get hold of a Motec dealer and put the question to them.
A lot of what happens with the GPR package updates, will come from the customer driven requests. So if they're getting a lot of requests for a certain feature, then it's likely that that will be introduced on a future firmware update. Scott has asked, with the initial data set shown for the evo drag engine, you showed the area of ignition retard and the engine was dumping unburned fuel and air. Would a byproduct of this be a cooling effect on the engine, especially just before a drag race? OK so there's two aspects of this. The actual combustion chamber temperature is probably going to be cooled to a degree because we do have unburned fuel and air ultimately going through cylinders.
The cut effect is randomised, so you'll always have a number of cylinders that are having the ignition cut so in those cylinders, the unburned fuel and air will be passing through. So there's a cooling effect from that. The problem we do have though is the cylinders where we are continuing the combustion because we've got the ignition retarded quite heavily, combined with the combustion process continuing to the exhaust, this does build a lot of exhaust gas temperature which can be potentially damaging so this is why I do suggest, if you're setting this up, that you do monitor exhaust gas temperature. You probably want to be very careful if you're getting up close to sort of 950 to 1000 degrees centigrade. Much beyond that, depending on your turbocharger itself, you can end up damaging the turbine housing and the turbine wheel.
So we wanna be very mindful of using any launch control strategy that involves ignition retard for prolonged periods of time. Alright that's taken us to the end of our questions now. So as usual if you do have any other questions that crop up that I couldn't get to here, please ask those in the forum and I'll be happy to answer them there. Thanks for joining us, I look forward to seeing everyone next time. Now for everyone who's joined us today, I just wanna mention as well, I should've said this right at the start, that because we are about to head to the USA for Pikes Peak, there won't be any of our regular weekly webinars for the next two weeks, so I apologise for that.
But yeah unavoidable unfortunately. Now for those who are watching on Facebook today, this is just a little insight into what we put on every week for our HPA gold members Our gold members are able to review these webinars at any time in our archive where we've currently got over 170 hours of existing content just like this. So this is one of the fastest ways to really expand your knowledge on a wide range of tuning topics, a wide range of ECU platforms, and a wide range of engines. If you're interested in becoming an HPA gold member, you can purchase gold membership on its own for USD$19 a month. It'll give you access to these webinars, as well as our private members only forum.
Alternatively you will get three months free access to our online community with the purchase of any of our courses. Alright guys thanks a lot for joining us, I hope to see you online again soon, cheers.