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Practical Reflash Tuning: Step 5-B: Optimising VTEC Changeover Point

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Step 5-B: Optimising VTEC Changeover Point


00:00 - One of the important aspects with tuning the Hondata K Pro is selecting the correct or optimal VTEC changeover point.
00:07 So this is the point in the rev range where the engine swaps from the low RPM cam lobes to its high RPM cam lobes.
00:13 So far during this worked example we have left our VTEC changeover point fixed.
00:19 And while I know that it was in the ballpark, now we're going to see how we can actually go about optimising this and finalising it.
00:26 It is relatively straightforward.
00:28 What we want to do is essentially perform two dyno runs, one with the VTEC changeover point set very low, and one with the VTEC changeover point set very high.
00:37 And what we're going to do is see a point where those two dyno plots either cross or at least disappear apart from each other.
00:45 And that's where we want to set our VTEC changeover point.
00:48 Now there are a couple of hints as well when we're looking at a dyno sheet, that perhaps our VTEC changeover point may not be optimal.
00:56 And this includes any area where torque and power dip right after or right before the VTEC changeover point.
01:04 Or alternatively where our VTEC changeover point, after this we see a very massive sudden gain in power and torque.
01:12 These are some hints that maybe something isn't quite right there.
01:15 So with stock Honda K20 engines we're going to find that the VTEC changeover point under wide open throttle occurs somewhere around about 5600 RPM.
01:24 Even in relatively stock engines while naturally aspirated, we're more likely to find the optimal VTEC changeover point is going to be somewhere between perhaps 4000 and 4500 RPM.
01:35 When we add forced induction with superchargers or turbochargers, that point will drop again quite dramatically.
01:42 That may be down somewhere in the region of 3000 to 3500 RPM.
01:46 So in this module we'll cover the process anyway.
01:48 As I've said, we want two runs with the VTEC changeover point set low and high.
01:52 On face value we'd think maybe we'll just set the low VTEC point to come on at zero RPM so it's always on VTEC, and maybe for the high RPM point we'll set it right at 8500 RPM at the end of our run.
02:05 Now we don't actually want to do that, this could potentially be damaging to the engine.
02:09 If we set our VTEC point too low, we can run into problems with potential oil pressure issues at low RPM.
02:14 This is because the VTEC system is oil pressure driven.
02:17 Likewise at very high RPM if we are still on the low cam lobes, this can cause problems with flow with the VTEC mechanism.
02:24 So generally it's a rule of thumb, I don't set the VTEC point to come in below 2500 or above 6500.
02:31 And we know that the correct or optimal VTEC point is going to be somewhere in that range.
02:37 So let's jump into our laptop software, and for our first run what we will do is set our high load VTEC changeover point to be 2500 RPM.
02:48 So this is our first VTEC changeover point and we're going to send that through to the ECU, perform a run.
02:53 Following that we'll come back into this parameter and we'll change that to 6500, upload that calibration to the ECU and perform another run.
03:02 Now I've already gone ahead and done that so let's jump across to our dyno and we'll see the results of those two runs.
03:08 So in blue we have our run with our VTEC changeover point at 2500, and our red run is at 6500.
03:15 So straight away if we just look at our red run, we can see a couple of the points that I was talking about here.
03:21 We're seeing that our torque is, or power and torque, they will both be nosing over here, just before this VTEC changeover point at 6500.
03:30 And then we see the massive sudden surge of power after the VTEC changeover point.
03:35 All good indications that something isn't quite optimal there.
03:38 And while these are very dramatic comparisons, we can also see the massive amount of power that is available here through the mid range if we've got our VTEC changeover point set incorrectly.
03:50 Alright so what we're looking for here is the point where these two lines cross.
03:55 Now we don't need to be too fussy about this initially.
03:59 There's going to be a little bit of settling and fine tuning here.
04:02 We can see that those two lines cross at around about 4500 RPM.
04:07 So what we're going to do now is jump back into our laptop software, and we'll adjust our VTEC changeover point to 4500 RPM, and we're going to send that through to the ECU and we'll perform another run.
04:19 So let's get that underway.
04:52 Alright so we've got our run complete there with our VTEC changeover point set to 4500.
04:57 And what we should expect to see here is essentially the best of the two previous runs and that's pretty much what we've got here.
05:04 In fact probably more of a run to run variation than anything.
05:06 We've actually see the third run, our yellow run, pick up a little bit of power around that VTEC changeover point.
05:13 Now one aspect here that we do want to try as well is bracketing that VTEC changeover point slightly.
05:19 So what we're going to do now is perform another two runs, we're going to try our VTEC changeover point set at 4400 and then also at 4600.
05:27 So this will give us three runs around our supposedly ideal VTEC changeover point.
05:33 So we can really get a feel for what is optimal.
05:36 So let's go ahead an we'll do those runs now.
06:33 Alright with our bracketed runs complete, we can now go across to our dyno and we'll have a look at our results.
06:38 Before we compare the individual results for our bracketed runs, I just want to point out now we've got a few more runs up there, we'll compare these runs with our VTEC point optimised to the first run we did, our blue run, where we had our VTEC point change over at 2500.
06:55 And we can see that the blue run actually starts to fall away at around about 3500 RPM or so.
07:02 And it actually lags quite significantly.
07:04 So we need to keep this in mind, this isn't uncommon to see this sort of situation.
07:09 So it is important to do some testing once we have set our VTEC changeover point or chosen our VTEC changeover point.
07:17 Let's get that out of the way for now.
07:19 And if we look at our three runs there, with our VTEC changeover point at 4500, 4600, and 4400, we find that while there isn't much between them, we actually get the best results if our VTEC changeover point is at 4500.
07:35 So this is how we go about setting our VTEC changeover point.
07:39 What we also want to do though is consider the tune around our VTEC changeover point.
07:45 What I mean by this is that for a coarse adjustment to our VTEC changeover point, we don't need to be too fussy about our fuelling and ignition.
07:54 Once we're starting to get down to the point of fine tuning this, we do want to be careful and make sure that our results aren't being thrown off by the air fuel ratio perhaps being excessively rich or excessively lean, just prior or just post the VTEC changeover point, this will influence our results.
08:11 So we wanna check our tune, make sure that that is on point.
08:13 One more point to consider when we are tuning our VTEC changeover point as well as the cam control around the VTEC point.
08:21 So I just want to show you the data from the last run we did with our VTEC changeover point set to 4400 RPM.
08:28 And if we look at what's happening here, the VTEC changeover point occurs right here at, we're just under 4500, but we can see particularly this step here in our cam timing.
08:39 And this is something we want to be careful of.
08:41 Now if there is a significant step between the cam target on our low cam map, and our cam target on our high cam map, as we step over to that VTEC changeover point, this can cause problems and we do actually have a little bit of this occurring here.
08:59 You can see that we've got a step, so pre VTEC changeover point, our commanded cam angle is 39 degrees.
09:06 And if we look just after that, it jumps to 45 degrees.
09:10 Now that's only six degree change, but of course as we've discussed already, the VTEC mechanism can't jump instantly.
09:17 And if we look at what's happening here with our red line for our cam angle, our measured cam angle, we can see that it does lag a little bit.
09:25 So one way we can deal with this is to adjust our cam timing or our cam targets pre or post VTEC changeover point just to account for that.
09:34 So let's have a look at how we can do that.
09:36 So we're clicking on the point here just after the VTEC changeover point, and we know that pre VTEC changeover point we were targeting about 39, let's call it 40 degrees.
09:46 What we can do here is go into our VTEC, our high VTEC cam target map here, and we can do this either on the high VTEC or low VTEC.
09:55 What we could do here is just adjust those zones that we're operating in there at 4500.
10:01 We can adjust these down to 40 degrees, so essentially they will match the target that we've got on our low VTEC changeover point.
10:09 Now once we go past 4500 we're gonna step up to our normal values.
10:13 And of course here we're only talking about five degrees.
10:15 But we could be in a situation where that VTEC changeover point sees a cam target swing of about 10, 20 or more degrees.
10:23 So once the cam swing gets larger, this problem becomes magnified.
10:28 And the other way we can deal with this as well, let's have a look at our low cam target map.
10:33 And we'r again up at our VTEC changeover point here.
10:37 So you can see that we were targeting 40 degrees.
10:39 What we can do here is we can actually adjust the points on our RPM scale.
10:45 So we can see over here we've got break points at 4000, 4500, 5000, etc.
10:50 So what we could choose to do here is make the break points a little bit tighter and we can do this by right clicking and clicking edit RPM index.
11:00 So instead of 4500, what we may choose to do is make this point 4200.
11:05 We could then make the next point here We'll make another one here at 4400.
11:15 And then finally another point here at Now we've got tighter control now over our cam target.
11:24 Remember it's 4500 where we are jumping up to our high cam VTEC changeover point or our high cam target.
11:33 So what we want to do there is then adjust and smooth the cam targets between our normal running point under low cam, and our running point under high cam.
11:45 So we can do this because we have added some resolution into our RPM index.
11:50 We can do this between let's say 4200 here and 4500.
11:55 So we could perhaps, let's say we were targeting 45 degrees, which we were initially, what we could do here is change our 4300 RPM target here to 42 degrees.
12:08 And we could change our 4400 RPM target to 44 degrees.
12:13 And then we're at 45 degrees above that.
12:17 So what we're doing is just helping to smooth out this little hump here and make the cam target consistent.
12:24 So we've seen two ways of doing this.
12:26 There's no right or wrong way of doing this.
12:28 Obviously we don't want to deviate too far away from the cam targets that we found gave us optimal power and torque on both high cam and low cam.
12:36 But by using that technique of adding some resolution in with additional RPM break points, we can quickly ramp into our cam timing targets that we're going to be at once the VTEC changeover point kicks in.
12:49 So at this point we should have a good understanding of how to optimise our VTEC changeover point on the dyno, and we should understand as well how to analyse and smooth our cam targets across the VTEC changeover point as required.
13:03 We're going to move on now and we're going to have a look at some steady state tuning.

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