Variable Cam Control Tuning: Step 5: Wide Open Throttle Tuning
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Step 5: Wide Open Throttle Tuning
25.21
| 00:00 | - The last step of our tuning process here is to optimise our cam targets under wide open throttle ramp run conditions. |
| 00:07 | And we do need to talk a little bit about where abouts in these maps we will actually be operating when we are under wide open throttle conditions, given that the car is turbocharged and we've got the ability to vary our boost pressure. |
| 00:19 | Let's have a look at our cam control target map for our exhaust and we know that under steady state conditions in the last step, we've optimised our cam timing out to about 25 kPa. |
| 00:28 | With this particular engine and turbocharger, on the minimum boost pressure we can run, the wastegate spring pressure, we're going to be operating somewhere around about 100 kPa, maybe slightly above that mark. |
| 00:40 | So this will be our minimum point in our cam target tables. |
| 00:44 | However with some electronic boost control added in we can raise that boost pressure up and all in we'd probably be expecting to run somewhere closer to about 150, 160 kPa through maybe 3500 to 5500 RPM. |
| 00:59 | Given that this engine does still retain the factory fuel system, injectors and fuel pump, we will need to taper that boost back in the higher RPM region so by the time we get up to 7000, 7500 RPM we're probably likely to be back around 110 kPa just to give us a little bit of injector head room. |
| 01:17 | Now for our purposes here, we will only be performing our tuning under wastegate spring conditions, so the minimum boost pressure targets, around that 200 kPa mark. |
| 01:27 | However, this is where we would always want to start and we always want to begin our tuning, just as we would for our fuel and ignition, at the minimum boost pressure we can achieve. |
| 01:36 | And we can achieve this, if we're running electronic boost control, either by electronically disconnecting the boost control solenoid or alternatively we can zero the boost target and duty cycle tables in our ECU to achieve the same aim. |
| 01:49 | Basically the process we would go through here is to optimise everything under our wastegate spring pressure conditions and then raise our boost pressure and we would then recheck our cam targets and reoptimise if required. |
| 02:03 | Generally as we start pushing the turbocharger harder and harder, particularly at high RPM and high boost, the exhaust back pressure will tend to rise and this can dictate a change or a required change in our target cam angle for optimal performance. |
| 02:19 | Generally the sort of changes we see if any are relatively minor but you'll be able to use the same bracketing technique that we'll demonstrate here in order to optimise your higher boost cam targets as well. |
| 02:31 | Alright so let's have a look at what we're going to do here so as I mentioned we've already tuned up to 25 kPa so this gives us this big hole here above 25 kPa or from 25 kPa and above and 5000 RPM and above which we didn't touch under steady state conditions. |
| 02:49 | And there's a couple of ways we can deal with this and it really comes down to personal preference. |
| 02:54 | First option would be to simply highlight the entire wide open throttle operating area here and set all of those targets to zero and then perform a range of ramp runs just like you saw in the body of the course, optimising both our intake cam timing, followed by our exhaust cam timing and then going back in an iterative approach to our intake cam timing. |
| 03:13 | Now nothing wrong with that but we already know at least in the lower RPM area that our cam targets are probably pretty close to optimal here, at least in the ballpark. |
| 03:24 | So another technique, one that I'm going to demonstrate here, is we're going to simply extrapolate the results we've got so we know at 4000 RPM for example in our exhaust cam timing map, 25 kPa and above, we wanted to be at -45°. We can expect that at 7000, 7500 RPM, we're going to probably end up with our exhaust cam and our intake cams back at or very close to 0° so what we can do is simply extrapolate what we're expecting there and we'll highlight 25 kPa, 7500 RPM down to 4000 RPM and we're just going to press the L key for linear interpolation and if we just grab our 3D map we can see that that gives us a reasonably sensible shape to our map, albeit it is quite squared off which is the result of that interpolation and that's OK, this will give us a good place to get started with our fine tuning. |
| 04:22 | Let's head over to our intake cam target angle table and we're going to essentially do exactly the same, 25 kPa and above, 4000 RPM up to 7500 RPM and just use that linear interpolation, again we've got the general trend and shape to that graph, albeit it is a little bit squared off. |
| 04:41 | Now of course this does give us this big area in both tables at light load, higher RPM where we've got zeros, don't worry about that for the moment, we'll see how we can deal with that once we've optimised our cam targets under wide open throttle conditions. |
| 04:55 | So I've already gone ahead and zeroed out our wastegate boost control duty cycle table so we're going to be on our minimum spring pressure and what we're going to do here, I'll just explain before we get stuck in. |
| 05:05 | We're going to use our bracketing technique that we looked at during the body of our course where we're going to lay down a base run with our intake and our exhaust cam targets exactly what we've just set them to and we're then going to bracket our intake cam initially, given that we know the performance of the engine is going to be more sensitive to more intake cam timing and we're going to make changes of perhaps plus or minus 5-10° and basically we're chasing the optimal results so we may find that there's a few iterations in getting this right. |
| 05:36 | Once we've got our intake cam as optimised as we can, we're going to repeat that process on our exhaust and we may want to come back and then revisit the intake once we've got the exhaust dialled in. |
| 05:46 | Given that we are starting from a target table that has a reasonable shape, we should be pretty close to the mark but we'll find how quick and easy it is to dial this in if required. |
| 05:58 | Now of course here this would be an iterative process that would also require fuel and ignition tuning to go along with this, we will not be detailing that as we go through this process and we will just be relying on using our closed loop control to keep our fuelling on target. |
| 06:14 | So let's get our engine up and running on the dyno and we'll lay down our base run. |
| 06:17 | Alright we're up and running, we've got rid of any heat soak, we're ready for our first run so let's see what our results are like. |
| 06:39 | Alright so we can see from our first run there, 271 horsepower at the wheels, 202 KW, just quickly checking our air/fuel ratio, we can see that it's a little bit lean right down in the bottom end but we've got no boost there, again I'm not really too concerned about that, our closed loop trims are pretty much picking up the pieces and we can see that once we're on boost we're sitting down pretty close to our target of 0.78 which is the reference line. |
| 07:03 | Boost pressure there, we can see that we peaked a little bit over 200 kPa so a little bit over 15 psi. |
| 07:10 | Alright so what we want to do is we'll save this run, and we're going to call this base run and that will give us something we can refer to, this will stay up on the screen for our subsequent run so before we make our next change or our next run, we will make a change so let's dive into our tuning software. |
| 07:29 | And what we want to do here is just make a change to our entire map in the area we're going to be running in. |
| 07:36 | Remembering at low RPM we were still down around that 25 kPa so I'm going to highlight the entire map here. |
| 07:43 | And the change we make here is really up to you, I'm going to start by retarding the entire map by 5° so we'll just take 5 out of the entire map. |
| 07:52 | We do need to be a little bit mindful when we're doing this. |
| 07:54 | It may be that we choose to advance the map, that's absolutely fine too but just bear in mind that particularly through that mid range where we already had values of 45° in there, 48, 49 degrees was about the maximum amount of cam travel we were able to get and of course if we targeted 50 for example we would run the risk of ending up with integral windup so just make sure that you retain values that are actually achievable. |
| 08:18 | Alright so 5° change there made, let's get ourselves back up and running, we'll perform another run and we'll see how that stacks up compared to our original run. |
| 08:45 | Alright so let's have a look at our results there and we've actually picked up a little bit of power, we'll talk about the peak power in a moment but hopefully what you're able to see during that run was that we did pick up power from around about 3500, 4000 RPM right the way through to about 6500 RPM. |
| 09:02 | Little hard to analyse this with the way the graph is represented during the ramp run so what we're going to do is we'll save this run and we'll analyse the 2 overlaid one on top of the other so it's always a good idea while we are doing this just to give a quick reference of what you've actually done so in this case we'll say intake minus 5. |
| 09:20 | Looking at this graph makes it much easier to analyse the real differences between those 2 runs and we can see straight away that particularly at the start of the run right up to in this case about 3900 RPM, there's really been absolutely no difference, we haven't benefitted from retarding the timing 5°, we haven't really been hurt by it either but we'll talk about that in a moment. |
| 09:40 | From 3900 RPM right the way through though we do see that we've gained power. |
| 09:46 | We do need to be mindful here of the potential for run to run variation so this is always a problem when we are on a dyno just making sure that the differences we're seeing on the dyno are a result of the tuning change we make. |
| 09:58 | We see they're at 7000 or 6900 RPM, about a 1.5 horsepower variation so let's just jump back into our tuning software and we'll see that 7000 RPM we have in fact retarded the timing there, we went from 6.4° to 1.4 so probably is actually a real gain there, it's probably not a run to run variation but any time you're seeing a power difference in an area we haven't affected the timing, cam timing, this is something we do want to watch. |
| 10:27 | So what are we going to do for our next set of changes? In this case we know that from 4000 RPM, or 4000 RPM was about the break even point where we started seeing a change, from there and above we saw a gain with the 5° of cam retard so what we're going to do is simply go further. |
| 10:46 | So I'll highlight in this case from 4000 RPM and above and we'll take out another 5°. |
| 10:52 | Now obviously there at 7000 RPM, we're at 1.5°, 1.4°, we can't take out 5° so let's just set that to 0. |
| 11:02 | Now in the bottom end there though, up to 4000 RPM we didn't see a benefit from retarding the timing so it's always a good idea to try going the other way. |
| 11:12 | So what we'll do is highlight from 1500 RPM, this time we'll go up to 3000 RPM and we'll try going back up the 5° that we took out and we know again we're limited to about 48, 49° so just for the sake of testing, let's try taking us up to 49° and just see if an additional 4° of advance actually helps that bottom end so let's perform another test now and we'll see the effect of that change. |
| 12:00 | Alright, our next run complete there, 274 horsepower at the wheels, was a little hard during that run to really pick the benefits as we went through so let's save the run again and we will analyse the results. |
| 12:14 | OK so now looking at what we've got here, remember that we advanced the cam timing a further 4° down in the low end and it does look like we actually have got a gain from this, the yellow line which is our last one has shown an improvement, mainly from about 3200 through to about in this case 4000 RPM but a gain nonetheless. |
| 12:37 | Again need to be mindful of run to run variations, particularly with turbocharged engines and make sure that that isn't as a result of additional heat in the exhaust manifold improving the turbocharger response. |
| 12:47 | So there's always little traps that you need to be mindful of when you are running a car on the dyno. |
| 12:53 | On the other hand, above 4000 RPM there's not really too much to get excited about except right at the very top of the run at 7000 RPM here we can see that we have picked up in this case it's showing about 5 horsepower gain so that's definitely something we'd like to keep. |
| 13:10 | Although again given the fact that we only retarded the timing at 7000 RPM by 1.5°, I'd be more inclined to think that this is likely to be an artefact of a run to run variation so it would probably be better to actually recheck that. |
| 13:24 | Looking at the rest of the run, there is a small gain between maybe 4500 and 5000 RPM. |
| 13:32 | Above that we actually did better with our previous run except right at the top end so let's try and apply some of what we've learned there so 7000 RPM, we do want to retain our 0° timing, again we'd just check and make sure that that isn't a run to run variation that's affecting that. |
| 13:51 | Then coming back there we know that 6500 RPM down to 5500 RPM in this case we'll take that to 5000 RPM, we did better with an additional 5° in there. |
| 14:04 | So we'll add that back in. |
| 14:08 | Now looking at our cam target table here, just making sure that we haven't got any really weird holes or anything in our table and it's looking pretty much consistent with the shape that I'd expect there. |
| 14:23 | So I'm pretty happy with that, what we'll do is lay down one final run there with our intake cam and we can move on and look at our exhaust cam. |
| 14:48 | Alright our final run there for our intake cam, 278 horsepower at the wheels. |
| 14:52 | Did notice that our boost response was very slightly slower to come in there but given that we didn't make a cam timing change at low RPM, I know that that wouldn't be a result of the cam timing so this is again just something we need to be mindful of. |
| 15:05 | The Subaru engines are particularly bad for this given the long exhaust runner length. |
| 15:09 | It's really important to try and keep your run lengths and time between runs consistent in order to make sure your results are as repeatable as possible. |
| 15:18 | For now though, we will move on and we're going to have a look at the same process on our exhaust cam so let's head across to our exhaust cam target table. |
| 15:28 | So what we're going to do here is essentially exactly the same process, we'll start by highlighting the entire operating area. |
| 15:35 | Again doesn't really matter if we advance or retard the cam timing to start with, we're just going to make a guess so let's take 5° out of that and we'll perform a run and see the effect of that change. |
| 16:05 | Alright so straight away we can see that that change is not the right change, we've lost a significant amount of power there, around about 12 horsepower peak and we were basically down just about everywhere. |
| 16:16 | So let's just save that run and we'll analyse the results over the top with our final intake run. |
| 16:23 | Alright so overlaying the 2 one on top of the other, we can see that we've basically lost everywhere, particularly right up at high RPM we've lost significantly so we definitely don't want to be going in that direction so let's head back into our target map and what we'll do is we'll add the 5° that we just took out. |
| 16:44 | Just like with the intake cam we do need to be a little mindful about how far we move the cam. |
| 16:48 | We were limited to around about 45° of movement on the exhaust cam so can't really change my peak values but what we can do is change the values above and below so let's first of all look at 5000 RPM and above and we'll take 5° out of here. |
| 17:05 | We will also try retarding the cam a little bit further before that. |
| 17:12 | And just see if we can get an improvement in our spool down at 2000 RPM. |
| 17:17 | Bearing in mind we're starting our run from 2000 RPM so it's hard to see a significant impact from that when we're so quickly transitioning through it. |
| 17:25 | Let's get another run underway and see what the effect of that change is. |
| 17:46 | Alright we can see that the change there's got us back at least where we were so let's save it and analyse it in a little bit more detail. |
| 17:53 | Alright so looking at our results there, we can see that potentially right up in the very high end up around 6500 to 7000 RPM we actually did see a benefit from retarding the exhaust cam an additional 5° so that's a good thing. |
| 18:09 | The difference there is minimal though so wouldn't expect we'd see results from going much further. |
| 18:15 | The rest of the run though we can see that essentially we've gone nowhere there, we've basically lost power everywhere. |
| 18:22 | We do still need to be mindful of we've got a slightly slower spool up there, again just heat in the exhaust manifold so that's the result of this variation we've seen down here at 3800 RPM. |
| 18:34 | But by the time we're at full boost we can still see that essentially we have lost power everywhere so basically the takeaways from this, the only place that it seems we really want to change our exhaust cam timing there is right up at the very top of our run so let's go and apply what we've learned there. |
| 18:52 | So first of all we made an additional change of 5° down here, 2000 RPM, hasn't really seemed to benefit us so let's just reverse that change. |
| 19:02 | Next we retarded the timing an additional 5° from 5000 RPM and above but we really only benefitted right at the top of the run out at 7000 RPM so what we'll do there is simply highlight the areas where we didn't see benefit and we will add 5° back in there. |
| 19:25 | Alright so let's have a look at the finished shape of our table there. |
| 19:29 | We can see that again it's showing pretty typical results to what we'd expect. |
| 19:34 | Alright with those changes made we can see that we've got a reasonably typical shape to our cam target table. |
| 19:40 | We do want to be mindful of any steps and we do see we've got a little bit of a step here and that's the one that we've literally just introduced in the way we made that change there. |
| 19:49 | We can choose to smooth this a little bit and we are really splitting hairs with the sort of change in terms of power that we were seeing there so again sometimes it can be beneficial to have a smoother table shape, even if we are potentially giving away a horsepower or thereabouts because it will make for easier time for the cam timing to actually track the target. |
| 20:13 | Alright so at this point given that we only made 1 very small variation that made an improvement to our exhaust cam timing and that was only 5°, very unlikely here that we're going to see further benefit from switching back and readdressing our intake cam so we're going to leave our intake cam tuning as it is. |
| 20:30 | And you can see this is the benefit of this bracketing technique. |
| 20:32 | We're already going to be starting from a position where our cam timing should be very close to our target so this kind of gets us away from the problem of having to iteratively move backwards and forwards between intake an exhaust cam timing. |
| 20:44 | If I'm seeing a required change to my exhaust cam of only 5° or thereabouts, it's very unlikely that there's going to be much gain to be had in going back and addressing the intake cam, it's only when we're starting to see the need to shift the exhaust cam by maybe 10° or more that this would probably coincide with a requirement to go back and revisit our intake cam. |
| 21:07 | So from this point for this example we're going to leave our intake cam tuning as it is. |
| 21:12 | Let's now discuss what we can do with the rest of our map. |
| 21:16 | Alright so we've got a reasonably smooth shape to everything but of course we do have this big hole in both our intake and our exhaust cam timing map. |
| 21:24 | It doesn't matter too much here in terms of being absolutely precise, there's absolutely no point in us spending a huge amount of time and energy getting our cam timing absolutely spot on in these areas. |
| 21:37 | Given that we don't operate our car at 6500 RPM in part throttle. |
| 21:41 | So yes we want numbers in here that are at least in the ballpark but we don't need to be chasing absolute precision here. |
| 21:48 | So what we're going to do is simply follow the trends that we're already seeing here in our table and we'll make some educated guesses here, probably going to be, if we're already at 5° at 7500 RPM, 25 kPa, probably with our trend we'll be back at 0 here so what I'm going to do is just use some linear interpolation here and that will give us a pretty good result that's going to at least be close enough for our purposes. |
| 22:14 | Right so now that we've done that, let's have a look at our finished table. |
| 22:19 | The only thing that I would potentially want to revisit is we can see in here we do have a hole in our exhaust cam timing map. |
| 22:27 | That corresponds to around about this area here I believe, let's just highlight that. |
| 22:32 | And we see that we've got -20 and we've got -20 here. |
| 22:38 | Now the fact that we've got -20, -20 and then -32.5 as we move up, that's a bit of an alarm bell and again just for the sake of tracking this nice and smoothly, what I'm going to do is just use the linear interpolation function to smooth that out. |
| 22:55 | And alternatively you could of course go back and revisit those -25 kPa sites and just make sure that you were in fact accurate. |
| 23:02 | In this case, using that linear interpolation makes a change of 6.2°. |
| 23:06 | Very unlikely that's going to translate to a massive difference in our power and torque and again if we get a smoother result as an outcome of that, definitely that's going to be beneficial. |
| 23:19 | So there's our finished exhaust cam timing target table for our STi. |
| 23:23 | Let's go ahead and do exactly the same to our intake cam. |
| 23:28 | So again just looking at the trends here, we can see that about 8° at 6500 RPM, probably going to be back down to 0 or maybe 2° here, we'll use our linear interpolation and again this may seem like I'm being quite blaze about it but the reality is it's just not that critical. |
| 23:48 | It's all about just having a smooth trend to this table. |
| 23:52 | If we've got a smooth trend to the table, an area that we're not going to be driving the car, the upshot of this is it's going to give us good performance for our cam timing, it's going to track nice and smoothly and that is going to be the outcome that we want, the result that we're desiring. |
| 24:08 | So looking through this again, this one does look pretty smooth. |
| 24:11 | We've got a couple of areas that I would also highlight, this one here is a bit of a peak that is this particular site here and again just for the sake of smoothing this, can be beneficial to go through and make some spot changes if we do see anything out of the ordinary and again you can do this by going back to that particular site and addressing it. |
| 24:34 | Or as I'm doing here, you can just make some spot changes to this. |
| 24:38 | Again we're making 1 or 2° changes, the benefit in terms of smoothness and cam tracking far and away outnumbers the, outweighs the gains that we may see in terms of outright power and torque. |
| 24:51 | So at this point we've got both our intake and our exhaust cam targets dialled in, we've got everything tracking really nicely. |
| 24:57 | Of course at this point the process now is to lock in any final changes required to both our fuel and our ignition timing and our worked example is complete. |
| 25:06 | Of course we'd also go through and check our targets at our higher boost pressure as I previously discussed. |
| 25:12 | If you do have any questions on this worked example, please feel free to ask them in the forum and I'll be happy to answer them there. |
