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Variable Cam Control Tuning: Optimising Inlet Cam Timing

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Optimising Inlet Cam Timing


00:00 - In this module, we're going to work through the steps involved in optimising our inlet cam tuning under wide open throttle ramp run conditions.
00:07 So this would be what we'd be completing once we've already gone through and optimised our cam timing under steady state conditions.
00:14 Obviously what we're talking about here, applicable solely to continuously variable cam control engines.
00:21 For our demonstration we're using our Subaru STi fiftted with our Ecumaster EMU Black ECU.
00:27 Despite this engine having quad variable cam control, the Ecumaster EMU Black only has 2 cam control outputs so we're using those to function the inlet cam timing.
00:37 For the purposes of this demonstration we're completely ignoring the exhaust cam timing that will remain fixed so it's exactly the same as tuning any continuously variable cam control inlet only engine.
00:49 Of course the table setups and the functionality of your ECU may differ but the process is going to be the same.
00:57 Let's start by jumping into the software.
00:59 We'll have a quick tour and get our head around what exactly we're going to be doing.
01:03 So at the moment we are on our VVT tab and we've already got what we can see here is a reasonably tuned cam target table.
01:12 We've got the graphical display of that out here on the right hand side.
01:16 And just looking at it visually for our intake cam timing we can see that at low RPM we've got 0° advance so running at full retard likewise at 7000 RPM up near the rev limiter we're also fully retarded which is pretty much what we'd expect from an inlet cam, likewise we can see around peak torque we're at about 40° advance.
01:37 We've got 50° of total movement so probably in the ballpark.
01:42 And when it comes to optimising our cam timing under wide open throttle ramp run conditions, more often than not, we will actually be working from a starting point that looks something like this.
01:53 And the techniques we use when we've already got an established table are a little bit different to what we'd be doing if we were starting from 0.
02:01 However for the sake of completeness we will start by zeroing this table out and we'll see how we can develop this table from scratch.
02:08 Given this is a turbocharged engine, for the purposes of our demonstration we will start by setting the entire table from in this case 111 kPa and above, we'll set that all to 0.
02:21 It is worth mentioning here before we move on that in this table we can see that essentially from about 156 kPa and above, we're really not seeing any notable changes in our cam targets and particularly from 179 kPa, let's call it 180 kPa and above, the cam targets are identical so this really comes into our table setup and our resolution or break points of that table.
02:47 Now it's not usual that we'll see big cam target changes with changes in our boost pressure although if you are pushing a turbocharger very very hard and the exhaust manifold back pressure is starting to climb excessively, that may dictate some changes to reduce your overlap but this is not unusual to see something of this nature.
03:08 Obviously we've got a turbocharged engine here.
03:11 If you were naturally aspirated you'd see something very similar.
03:14 Obviously we're only operating in pretty much one column at that point, either 100 kPa, there or there abouts or 100% throttle and we'll probably see from maybe 70 or 80 kPa or maybe 70% throttle and above, again our cam targets are relatively fixed so just understanding the likely layout or likely nature of the table is important so you're not going to end up with any surprises.
03:39 Right so let's start here by doing exactly what I mentioned, we'll highlight the entire table down to 111 kPa and set that all to 0.
03:48 Actually for the sake of completenss considering we've only got 1 column remaining, we'll set the entire table here to 0.
03:56 Alright so that's set our starting point, now before we do our first ramp run here on the dyno, it is worth also mentioning that we're going to expect to see some variation here in our fuelling as a result.
04:07 Given that this particular course is focused on the cam timing, we're not going to dive too much into the fuelling but it's worth understanding what's going to happen here.
04:15 Particularly in this mid range here where we were around 40°, 38° of advance, we've pulled that all the way back down to 0.
04:23 What we can rightly expect here is that we will have massively reduced our volumetric efficiency.
04:30 Now on a speed density operating system, if we now don't make any appropriate changes to our fuel or VE table, we can expect now that our fuelling in that mid range should go very rich.
04:42 Now is that going to be a problem, well not particularly given that was not a lot of point wasting time optimising our fuelling at 0° cam advance and 3000, 4000 RPM.
04:54 We know very well that we're not going to want to end up with our cam timing anywhere near 0° so there's not a lot of point optimising everything for a condition we're just simply not going to be running in.
05:06 That being said, we obviously want to monitor the air/fuel ratio, make sure it's not excessive to the point that it's going to end up fouling spark plugs or causing a rich misfire that's going to make it impossible for us to continue our tuning, Couple of ways around this.
05:20 We can manually make changes to our fuel table to accommodate or most aftermarket ECUs these days do give the option of closed loop fuel control.
05:29 Enabling this will let the ECU do some of the heavy lifting in the background and we can give the ECU a reasonable amount of power here to trim the fuelling maybe plus or minus 15-20%.
05:41 It might not be perfect but that should get us through and we're looking for a time efficient manner of doing this so that's what I've enabled here.
05:47 As we go through, we will at least be looking at our fuelling to see what's tracking there and what's happening.
05:54 Alright so we're set up for our first run here, let's head over to our dyno and we'll get our engine up and running and get our first run underway.
06:18 Alright we've got our first run complete there, just looking at the dyno screen we can see that we ended up with 285 horsepower.
06:24 Looking at our fuelling its not perfect but monitoring it as we go.
06:28 We can see that it's at least in the ballpark, certainly not dangerous to a point where I would be wanting to abort the run.
06:34 And we can see at least once we start getting up towards peak boost here, our fuelling is sitting pretty close to our reference line of 0.80 so not too bad there.
06:45 Let's jump into our laptop software and we'll see what we had going on there.
06:49 So first of all just looking at our logging for our VVT, just important to make sure that the cam timing is actually doing what we asked it to do.
06:58 So we can see here the green line here or green reference for our cam angle bank 1 and the brown line for our cam angle for bank 2 and we can see, no big surprises here, sitting at 0° right through the run so pretty happy with that.
07:13 Obviously exactly what we asked it to do.
07:15 Let's also just have a quick look at our fuelling here so we'll come over to our fuel tab and we can see pretty much exactly what we expected here, particularly in the low RPM region we can see that our fuelling in green is sitting quite a lot richer than our purple target so in this case the area that I've just highlighted there, our measured lambda, 0.84, our target 0.92.
07:39 Now again we could clean this up but we're at 4500 RPM, we just know that we're not going to be at 0° cam timing so I'm not particularly worried about this.
07:49 It is worthwhile just understanding though that if we do get close to the ballpark we're going to be running in, obviously we want to maintain all of the other parameters as close to being consistent as we can.
08:01 In other words, when we're changing our cam timing, we want that to be the only parameter that's actually affecting our power and torque so we need to maintain as close to the same boost pressure, as close to the same air/fuel ratio and of course ignition timing as we can.
08:16 Now of course as we change the cam timing, that in turn has an iterative knock on effect as we learned on our ideal ignition timing and our ideal air/fuel ratio but we'll get to that as we move through.
08:28 Alright so our first run out of the way there so that's our reference run here.
08:31 And what we're going to do is we're going to save that run and what we're going to do is call that 0°.
08:39 So this is just going to give us a reference that we can come back to and we're going to be overlaying all of these runs so we can get a sense of where we want our cam timing to switch.
08:50 So what we'll do now is we'll save that run, that's actually going to stay up on the screen which is going to be interesting because we'll actually start to see a sense of what's actually happening as we move our cam timing.
09:01 Alright let's head back to our VVT and what we'll do now is we'll highlight that entire operating area, 1300 RPM, 88 kPa and above.
09:12 Let's set that cam timing to an across the board flat 10°.
09:17 Now let's do another run and we'll see the results of that.
09:37 Alright second run complete there and we've got 290 horsepower, the more interesting thing though was seeing how much more power and torque, particularly in the lower RPM region of that run we had compared to our first run at 0°.
09:50 In fact really there was no loss anywhere running 10° instead of 0.
09:55 Let's jump quickly into our laptop software, we'll see what our cam timing was doing and as I just move through this ramp run we can see essentially both cams very close to our target there so pretty happy with that.
10:08 We'll just have a quick look at our fuelling and our fuelling, pretty close, we're still a little bit rich down in this mid range here, we can see the brown parameter that we've got here is our exhaust gas oxygen correction so the ECU pulling a little bit of fuelling there but as we move through, particularly once we're up above above 5000 RPM, the trim is within about 1 or 2% so the closed loop control, doing a reasonable job there and again my fuelling is on track.
10:37 Alright so we're going to speed up the process here because it's now a rinse and repeat, what we're going to do is we'll save that particular run and understandably we're going to call that 10° what we're going to do now is step up in 10° increments all the way through to 50° which is the maximum travel and we'll then be able to overlay all of those runs together and get a sense of what our cam timing actually wants to be so let's go ahead and do that now.
12:03 Alright so we've got all our runs complete there.
12:05 Particularly as we started to advance the cam timing further and further we saw that we picked up more and more mid range response, particularly with our boost as well, our boost was coming in much earlier than our first run with our fixed timing at 0°, however we did also start to see the power roll away and drop off at higher RPM.
12:25 Exactly what we'd expect as we advance that cam timing.
12:28 So now what we've got displayed here on our dyno screen is essentially a composite of all of those runs that we've just done, all 6 runs.
12:36 We can see we start with our blue run and this really highlights the point that we've located right now, just how powerful this is.
12:45 Our blue run there, we had 135 horsepower being measured.
12:50 The white run which in this case was 40° cam advance, we've picked up to 251 horsepower so over 100 horsepower gain with our cam timing.
13:02 However looking at the downside of this, our purple run right here at the top, 183 horsepower vs our peak there, blue and red essentially 0 an 10°, there's really not much, a bit of a coin toss between the 2 of them but essentially 282 horsepower so getting this right as you can see here is so important.
13:25 Alright so what we're going to do now is start building up a bit of a composite map.
13:29 So what we're looking for here is essentially what our cam timing wants to be at each point and we're just looking for the line that is the highest.
13:38 Now we can see that in this case our purple line here which is 50° advance, that is our peak value or our best power up to around about this point here, about 4500 RPM.
13:52 Now it may be that we actually do want to make a few compromises in this which we'll talk about but for the moment what we'll do is we'll just set the table to what the dyno is showing us.
14:02 So in this case we started our run from about 2000 RPM so closest thing we've got to that is 1886 RPM, obviously our entire table is currently set to 50°.
14:14 So I'm going to leave that there.
14:16 The point where we cross over though is 4500 RPM as we've highlighted and we want to be at 40° from 4500 RPM to approximately this point here, about 5000, 5200 where we switch to 30°, our green line as you can see overtakes that.
14:33 So let's find our point here, so we don't actually have a break point at exactly the point we want but let's just alter that so we do, so we'll make this particular point here 4500 and then we can make this particular point here 5000 RPM.
14:50 So we know that for those particular zones here, we wanted to be at 40°.
14:58 Now looking back at our dyno sheet here, dyno printout, so from 5000 RPM our green line is highest all the way up to in this case about 6000, maybe 6200 RPM.
15:12 So let's make our next point here, we'll change our break points here, we'll make them a little bit more sensible, 5500 and then we'll make 6000 RPM and we can always manipulate these as we see fit so we're going to be at 30° between these 2 bounds here.
15:32 Looking back at our dyno graph we can see we're starting to split hairs at higher RPM and we don't need to be perfect here because our next of bracketing will help us really fine tune this so we can see let's say our yellow 20° is the best up until about 6500 RPM.
15:53 So let's just change our break points again.
15:56 So we're going to enter that as 20°.
16:03 And then as we advance up we can see our red line here is superior, right at the very end of our run, 7000 RPM we actually see the blue, our 0° and our 10° are essentially giving us exactly the same power.
16:19 Chances are though if we'd run the engine out to 7500 RPM we might expect to see the 0° advance give us a little bit of a benefit but again just for simplicity let's give the engine exactly what the dyno sheet shows us we want.
16:34 Alright so we've got a pretty basic setup in here at the moment based on our composite timing that we've just developed using those 6 runs.
16:41 There are a few problems though and what we can see here is if we look at our graphical view we've got a pretty choppy sort of table and again we need to be mindful of the fact that this is a mechanical system, it's not going to do a great job of jumping 10° instantly.
17:00 It'll track that reasonably well but sometimes we might end up seeing that the dyno's calling for a change of 20° over quite a short RPM range so often it can actually be worth compromising this a little bit and actually smoothing so by that what I mean here is we might want to set this particular row to 45°, we may want to set this particular row here at 5500 RPM to 35°.
17:27 Now we might on paper be giving away a small amount of power and torque but the advantage here is if the cam timing can track target more accurately probably going to end up with a more drivable car out of it and really that's more important often than a small paper increase on the dyno alone.
17:43 Alright with our basic table set up now, let's get back up and running, we'll perform a ramp run on the dyno and see first of all how close to our theoretical optimum we've got and also how we'll we're tracking those targets.
18:14 Alright so we can see that we've got our first composite run on the dyno now and we can see overlaying with the previous reference line in purple which was 50°, gave away a little bit in the bottom end but that's probably more to do with run to run variation due to heat soak, again really important when we're doing something so sensitive like this to make sure that our engine operating parameters are held as close to the same as we can from one run to the next.
18:38 This means our engine coolant temperature as well as our intake air tempeature.
18:42 Particularly with a turbocharged car, when we are doing multiple back to back runs, this tends to build more heat into the turbo and exhaust manifold which can result in a slight increase in our boost pressure, particularly our boost response at low RPM so that's essentially what we're seeing there but we can see that we've got pretty good control of our fuelling here, boost pressure's doing pretty much what we'd expect, let's save that run now and we'll overlay this with our other runs.
19:19 Alright so our run we've just done is actually pretty hard to see, it's in red here and we can see for the most part it's pretty much skirting across most of the tips of all of our other runs.
19:33 Again, little bit of variation here, run to run but that is to be expected.
19:37 So what we're going to do now is go through the process of optimising what we've got on the screen right now, seeing if we can get any improvement, any gains.
19:46 And this is probably the point you're going to come into if you have already got a developed map.
19:53 So there's 2 techniques that I'm going to use here, the first of these is we're going to come back into our timing map here and let's look at what we saw on our graph or our logger from our last run, we can see our cam timing for bank 1 and bank 2 as I scroll through this and we can see these sort of steps which obviously are doing exactly what we've got on the cam timing map.
20:15 But what I'm going to do to start with is just smooth these a little bit, just going to change these break points which of course if you've followed the process through, this should be done a little bit earlier in our process anyway but we can always change these as we see fit and often this is important when we do start making changes to our cam timing during these ramp runs.
20:39 So what we've done now is we've just made those break point changes and you can see that the ECU has made some small changes here to interpolate those results, not too worried about those changes there but what we're going to do is make some of our own here.
20:52 I'm just going to go ahead and basically interpolate these so that I'm going to smooth off that shape and that's going to again as I've mentioned, make it a little bit easier for our cam timing to actually track these changes and smooth as generally what we're trying to achieve with this sort of change.
21:11 So that's our first change there, just doing some smoothing but we want to make sure of course that we haven't gone backwards with that change.
21:17 I've just made some general smoothing but that might actually mean that I've smoothed the wrong area so just want to make another ramp run here and just make sure that we're at least on track with our last one so let's go ahead and do that.
21:46 Alright so we've got our run complete there with our smoothing done and essentially we saw no real change there, we're at least within the ballpark of a run to run variation and that's going to lead us into our next step which is what I refer to as bracketing our result.
22:02 So we've got some numbers in that cam timing map that are pretty close but we also did take reasonably broad steps there in 10° increments for those 6 initial runs we did.
22:12 So regardless whether I've developed the map in the way that you've just gone through or I'm starting from a map that I've previously developed, maybe we've made some hardware changes on the car and we just want to see if the cam timing is still dialled in accurately, what we're going to do is make some block changes.
22:29 So we're going to get our reference run up on the dyno screen which obviously now we have, we're going to start by making a 10° change, it doesn't really matter whether we advance or retard the cam by 10°, we just want to make a change and see the effect of that change so let's start by removing 10° from the entire table here, so we've done that now and let's get another run underway and assess the effect of that change.
23:12 Alright so watching what was happening during that ramp run there, we could see that from around about 5000 RPM and above we actually picked up a little bit of power.
23:24 Didn't see a significant change in the bottom, maybe a slight loss so let's just have a better look at those 2 runs overlaid on top of each other.
23:32 So this makes things look a little bit clearer and we can see as I mentioned from about 4800 RPM and above there's a clear advantage retarding the cam timing 10° there.
23:44 We can see that we have lost a little bit through this mid range but again we do need to be mindful of making sure that this isn't a turbo heat related issue so couple of back to back runs just to makes sure we are seeing that repeated before I actually made a change would be the course of action that I take here.
24:00 And likewise we can actually see that our -10° has given us a bit of an advantage right down at the start of that run up to about 3000 RPM so let's apply what we've learned there.
24:10 So up to 3000 RPM we want to leave our cam timing as we've just left it.
24:16 So from 3500 up to about 5000 RPM, we want to advance that cam timing back to where we had it so we'll highlight that area there.
24:28 Now we need to be mindful of this because if I just add 10° here, going to see again we're getting into the situation where we're making some pretty ugly steps in this table which probably not going to give us the exact result we want so again it's a case of making these changes smoothly.
24:47 And again we can build this up so what I'll do is I'll start by just interpolating the results here between 4500 and 5500 RPM.
24:55 In the Ecumaster software we can do this using the interpolate vertical function.
25:01 That gives us a slightly smoother result here and likewise we will want to do something similar down here, it's probably actually not so bad here, 3000 RPM.
25:11 What I might do is just increase the values there just to give us a slightly smoother shape in that table.
25:19 So we're just watching while we're doing this, making sure that we haven't got any really ugly changes in this table.
25:25 So again we're at the moment trying to follow the exact peak values we're seeing on the dyno, this becomes an iterative process but let's get another run underway and see how we're looking.
25:53 Alright we've got our next run complete there so what I'm going to do is save this and we'll overlay these with our other composite runs and see how we're tracking with our results.
26:03 Alright we've got 3 of our composite runs being displayed on the dyno screen, our yellow run called composite 2 there, this was essentially developed from those 6 individual runs, building up our cam target table.
26:15 We've then got our green run here which is where we have removed 10° and then our composite 3 table which is what we've just done, our composite 3 run, our last run we've completed there which is where we've basically taken the wins that we saw from retarding the cam timing 10° and then done some smoothing.
26:35 So we can see for the most part our white run here, if we get rid of our yellow run, our white run here, essentially has given us almost the best of all of the results.
26:45 We've got a small deficit through this mid range here from around about 4800 RPM through to about 5500 RPM.
26:55 We are showing a little bit of a decrease.
26:57 We've seen an increase through this 4000 to 4500 RPM region and we can actually see we've also dropped off right at the top end.
27:06 Now this is where we need to be a little bit mindful if interpreting our results though because particularly for those last two runs, I made no changes to the cam timing at high RPM at 7000 RPM so we rightly wouldn't expect to see that so that's a clear indication that we've probably got some run to run variation creeping in here.
27:26 Most likely to do with rising intake air temperatures given our Subaru STi, it is quite difficult to maintain very consistent intake air temperatures with the top mount intercooler.
27:38 But the process we're looking through here is a essentially a rinse and repeat of this.
27:42 We're just going to make bracketing changes like this.
27:45 Now that first change we made there by removing 10° or retarding the timing by 10°, that actually in our instance gave us some pretty significant gains.
27:54 Often that won't show any improvement so of course if that's the case, we're going to go the other way, we'll advance the timing by 10°.
28:01 So we're bracketing each side of the initial composite map that we've developed and just seeing where we've got some iterative improvements or maybe some losses, applying what we've learned to our comosite table, our timing table and then repeating the run so in this way it is an iterative process of building up our optimal cam timing table.
28:20 Now of course once we've got that cam timing table pretty close to optimal, this is the time to then go back and reassess our fuel delivery, reassess our ignition timing, optimising those.
28:33 You may find that there are small improvements available, particularly with our ignition timing and once you've optimised the ignition timing it is worth going through another iteration of our bracketing, probably this time we should be very close to the ballpark so advancing or retarding 5° instead of 10° is worth just seeing if there is any small improvement.
28:54 But again just to reiterate the importance of getting our run to run conditions as close to ideal or consistent as we can.
29:03 We are potentially looking at quite small improvements from our cam timing, particularly when we're getting down to making 5° changes, so of course it's worthwhile making sure that all of our other variables are held as consistent as possible, our air temperature, our engine coolant temperature, our air/fuel ratio, our ignition timing and of course our boost pressure.
29:23 As we're going through this process, it is also worth checking consistently to make sure that your cam timing is actually tracking the targets that you're programming in so let's quickly have a look at that last ramp run from our tuning software and we can see here we are on our VVT tab and we can see our intake cam 1 and our intake cam 2, both following those targets really really nicely so nothing to be worried about here but this is an area where quite often we can fall into a trap if we aren't actually tracking the targets as accurately as we think.
29:59 Alright so that's the process we're going through here, let's head back over to our VVT target table and we do need to just address the fact that we've got some pretty ugly areas in this table.
30:11 First of all we can see here down at 1300 RPM to 750 RPM, we've got this massive step.
30:19 So we're not going to be tracking or asking for a cam advance at very low RPM because of our low oil pressure so generally 1300 RPM, we're getting into a region where we might be able to get some reasonable cam control, what I'm going to do is just increase this particular break point here to 1500 RPM.
30:40 And what we're going to do, instead of tracking a target of 40° here, we're going to actually reduce this down to make it a little bit more realistic, 20° so now we can see we've got a really nice smooth shape to that and that's going to make it easier for the system to track.
30:56 The other aspect that we do need to mention before we move on is that fact that for our demonstration here we've made really simple block changes so we haven't varied our cam timing there in respect to our manifold pressure at all, we've just run the same timing irrespective.
31:11 With a turbocharged engine it's worth understanding where about we are moving through this table.
31:16 So we start somewhere like here and we're going to be tracking up to about 250 kPa and then as the RPM increases, we're actually tracking back down.
31:26 So what I'm getting at here is that 4500, 5000 RPM, we may find that the idea cam timing is in fact 42, 34° but we may find that down in the lower load areas that the cam timing wants to be something significantly different.
31:43 Now of course in general we're actually going to be building up our steady state timing targets first and we'll already have addressed this lower region of the table.
31:52 But it's important just to explain that we're just making these block changes for simplicity for this demonstration and we certainly wouldn't want to leave our table with these large steps that we're seeing here so this is not representative of a real world table, it's just for the purposes of our demonstration.
32:11 The other aspect with the block changes we've made is that we can see that we've got this big ugly step here down at low load.
32:19 Now of course that's not representative of what we want there, stepping between particularly here 0 and 45, 48° across a relatively shallow change in manifold pressure.