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Launch Control: Two Step Launch Control Tuning

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Two Step Launch Control Tuning

15.10

00:00 - Now we're going to have a look at tuning the Launch Control function and we're gonna do this in two parts.
00:06 We're gonna start by looking at the simple two step style of Launch Control.
00:13 So the first thing we need to do here is set up our Launch Control Mode as Single Launch RPM which we've already done and the other thing we're going to do is set our Launch RPM.
00:27 Now I'm going to start with a Launch RPM of about 4500 RPM.
00:33 and we're just going to see how that works out.
00:36 I mean by that is when we're tuning we'd prefer to start with more RPM rather than not enough and it's going to probably result in the car breaking traction and just ending up wheel spinning but that is also easier on our drivetrain than having the car bog down.
00:53 So we're going to set that up at 4500 RPM and we're not going to be using any ignition retard at this point.
01:02 We will talk though that shortly but at the moment we're just going to leave that as it is.
01:08 I'm going to be using the Ignition Cut style of Launch RPM Limiter and I'm going to disable the Advanced Mode.
01:17 And realistically for most of your tuning you shouldn't really need to use the Advanced Mode.
01:23 It's really the Standard Mode of limiting is more than adequate for all of the instances I've really found unless you want to specifically adjust the Limit Style to suit your taste.
01:37 In that case you can do that through the Advanced Mode.
01:40 So what I'm going to do now is we're going to just do a test launch of our car and see how it responds.
01:50 And what I'm going to do while we're doing there is we will log what's going on so that after we've done the launch we can go back and review our data and make changes.
02:01 However, remember when we do this after we've launched the car as soon as we've let go of the clutch there is going to be nothing the ECU's going to be doing to help control that wheel spin, so that's really all down to the driver.
02:14 So let's see how we get on.
02:16 (revving) (squealing) Okay, so that worked pretty well exactly as expected.
02:28 What we ended up with was quite an excess amount of wheel spin.
02:33 It certainly wouldn't have been anything that would have helped our acceleration times.
02:38 So what I'll do is I'll just shut down the car and we'll have a look at what we've got in our data logging.
02:45 So first of all I'll just zoom-in.
02:48 We've got on this particular trace we've got our Engine RPM on the top.
02:52 What I might do is we'll just adjust the properties and I'll get rid of Manifold Pressure and I will add in Throttle Position just so you can see exactly what I was doing on the throttle.
03:08 At the bottom here we've got our Diven Wheel Speed and our Non Driven Wheel Speed just so we can see exactly what the wheel speeds are doing.
03:15 Okay, so you can see that I'm at full throttle here and the RPM comes up and it sits at our Launch RPM, give or take we're sitting at about 4400 RPM.
03:29 I think if I just jump back into our tuning.
03:32 Yeah, we'd set that at 4500.
03:34 That is actually one thing with the link as well the way the Rev Limiter works on the link is the Control Range occurs below the RPM that you set.
03:46 So if you have a 300 RPM Control Range the EC will actually start your Limiting Function 200 RPM below the value you put in your table.
03:56 So it's important to understand if you're getting confused as to why your Launch RPM is a little lower than you would expect or a little different to what you'd expect.
04:06 So the other thing we can do is add in here our Clutch Position just so we can see exactly when the clutch has been dropped or engaged.
04:17 So we can add a group here and we'll add Clutch Status onto our graph.
04:26 And you can see now, exactly the point where the clutch was released.
04:31 And at that point the RPM starts to increase and you can see that I'm still at full throttle.
04:36 What you can see though at the same time is the rear wheel speed or Driven Wheel Speed is increased dramatically.
04:45 We've got up to 53 kilometers and now on our rear wheel speed and our front wheel speed is just barely moving at 2.8.
04:52 So we've got an exceptional amount of wheel spin and you can see what I've done there is I've manually ended up removing my foot out of the throttle to help control that wheel spin and at the same time we're sitting up on our Engine Rev Limiter.
05:08 So this is an effective launch.
05:10 But it was to illustrate a point.
05:12 This is what we would expect to see if we've got our Launch RPM set way too high.
05:18 Now what we can do is start bringing that back and seeing how the engine responds So let's do that now.
05:25 We'll go back to our training.
05:26 I'll start the car up again.
05:30 This time what I'll do, this car we found launches reasonably well from even quite low RPMs.
05:37 So what I'll do is I'll set the Launch RPM at 2500 RPM and we'll start the data logging and we'll do another launch and see how 2500 RPM works.
05:49 (revving) (squealing) Okay, so even from the seat of the pants that time the launch felt better.
06:03 And if we look at our data logging, I'll just shut the car down again.
06:09 And I'll zoom-in so we can see exactly what was going on.
06:12 You can see that we're sitting here at 2400 RPM.
06:17 And you can see this time RPM rises being much, much slower.
06:22 We've haven't just bounced straight up onto their Engine Rev Limiter.
06:25 The car's actually started gaining some momentum and you can see also from the rear wheel speed we haven't jumped straight up to that 53 kilometers an hour we initially saw.
06:38 We've got a much better launch from dropping that RPM in effect my next move here would probably be to drop it even further.
06:48 The problem we've got and this is really the situation with the two step style of Launch Controllers, again once the clutch has been released and the car's moving there's nothing the ECU can do to help control that engine power.
07:03 So that's being back up to the driver to adjust the throttle position.
07:07 Just another point that suggests that that launch was far better you can see on our Throttle Position trace here I've actually managed to stay at wide open throttle and that's because the wheel spin wasn't so excessive.
07:19 It wasn't just straight up on the Engine Rev Limiter.
07:22 Okay, so the next step would be to change that Rev Limiter a little bit further.
07:29 Once we start getting closer to an ideal point we can start making smaller changes of perhaps 100 RPM at a time.
07:38 Using the data logging and analyzing the acceleration times we can start getting a feel for what a particular car wants to see.
07:47 Now I have a quick look at how we can use the Ignition Retard Function.
07:51 Now, obviously again, this car isn't turbo charged so we're not going to be expecting any boost but I will show you how that function works if you do want to use it.
07:59 So we've got our Ignition Mode in the moment set to Single Zone.
08:04 We'll look at tables shortly, but for the moment Single Zone is the simplest way of controlling it.
08:09 And we're going to have or ignition retard in degrees.
08:13 Now this really becomes a personal preference as to how you want to deal with this.
08:17 It doesn't really matter what your preference is as long as you understand the implication you're of whether you're using degrees, degrees absolute or percent.
08:26 So that can be adjusted to suit.
08:29 Now the Ignition Trim activation we can choose the throttle position and RPM above what the Ignition Retard will come in.
08:38 What this means is when we put our foot on the clutch when we're moving up to the start line, no ignition retard will be used so the engine will still respond normally.
08:47 And it will only, the ignition retard will only come on we actually want that.
08:52 So typically I might set this to say 80 percent.
08:55 For this cut test I will just set our launch RPM up to 4500 and we could perhaps set our RPM activation point at 4000 RPM.
09:07 What that means is our ignition retard will not come in until we above both 4000 RPM and 80 percent throttle.
09:15 Now we've got our actual ignition trim so this is the amount of timing that will be trimmed onto our table value.
09:22 So if we want to retard timing we need to enter a negative value.
09:27 So just for the purposes of our demonstration let's retard the timing by 30 degrees.
09:32 Obviously again this isn't going to actually have any effect on this particular engine.
09:37 So what I'll do is I'll start the engine (revving) And we'll just see up some logging so we can see exactly what's happening with our ignition retard.
09:49 And what I want to do is add a add another parameter so we can monitor what our ignition timing's doing.
09:58 I'm going to add a group and we will select Ignition Angle.
10:05 Okay, so now we'll be able to see the Ignition Angle as well as our Clutch Position and our engine RPM.
10:10 So what I'm going to do is I'll put my foot on the clutch you can see that's active and I'll just slowly bring the RPM up at minimal throttle to our Launch RPM limit.
10:21 (revving) Okay so you can see with a very small amount of throttle just 25 percent we've still got 30 degrees of ignition timing.
10:33 If I go to full throttle though (revving) (revs slowly) You can see that as soon as I did that the ignition is retarded and in that case we ended up going all the way to six degrees after TDC.
10:49 So we can tune that amount of ignition retard to adjust the amount of boost we're achieving depending on how large the turbo charger is and how much boost you want to acheive.
11:02 So that's how we can use the Ignition Retard in the Single Zone Mode.
11:09 Now, we'll quickly look at how we can set that up if we wanted to use the table instead.
11:14 And we'll just start as soon as we chose the table value, a Table Mode the pop-up box asks if we'd like to clear the Launch Control Retard and set the values to zero and the axis to default.
11:29 I'm going to chose yes, and now you can see we have the Launch Ignition Retard table option.
11:36 Now what we've got here is the table of RPM versus Throttle Position.
11:42 Now we can set this up however we want.
11:44 When we've got zeros in this table what it means is that it will make no change to the ignition timing being used the ignition timing from the main table.
11:55 So it's just going to be using the normal ignition timing.
11:58 When we put negative numbers into this table it will retard the timing.
12:03 Now a way that I tend to use this, and this is quite common for drag racing is we can set the axis up instead of Throttle Position we could set it up to be on Manifold Pressure.
12:16 And I'll just initialize that axis there.
12:19 And what we've got now is an axis that is RPM relative to manifold pressure.
12:27 Now what we find is with very large turbos and we talked about this in the body of the course with very large turbos we may want to use quite a lot of ignition retard initially just to get the turbo charger spoiled up.
12:40 Once the turbo starts spoiling it sort of becomes self-supporting and we won't need quite so much retard.
12:47 So with this sort of system what we could do is again, let's say that our Launch RPM is 4500.
12:55 So again, we don't want to use any retard down in the cruise or idle areas because that will make the engine response laggy.
13:04 So at perhaps at 100 kPa and again, I'm assuming here that our engine's actually turbo-charged, at 100 kPa we might want to remove 30 degrees timing.
13:16 Well, actually maybe let's go 40 degrees.
13:18 So that'll pull us well back after TDC and help start the turbo spoiling.
13:23 But let's say for arguments sake target boost for sure is 60 kPa gauge or 160 kPa absolute.
13:31 So what we can do is as we come up towards that target we can start reducing the amount of retard that we've put in there.
13:39 So instead of 40 degrees now we're at 30.
13:42 So we're putting some timing back in.
13:44 At 160 kPa our target might be we might only need 15 degrees of retard and then as we go above that maybe we could drop that down to minus five degrees and then finally at 200 kPa we'll be back to table values.
14:00 Now, how that's going to respond is when we put our foot on the clutch and we go to full throttle we'll straight away jump to our Launch RPM 4500 RPM and 100 kPa.
14:10 Now if the engine was turbo-charged we'd end up with a large amount of retard it would very aggressively start driving the turbo charger and would move down through this table as that boost started increasing.
14:21 But as the boost starts to increase you can see the retard is reduced we're actually putting timing back and moving back towards our main ignition timing table values and that will sort of remove that tendency to drop the turbo so hard.
14:37 And if we tune this correctly we can actually use it essentially as a type of boost control.
14:43 And we can quite accurately control the amount of boost pressure we have sitting there on the Launch Control.
14:50 So for those of you with turbo-charged cars and particularly those drag racing this is a very powerful function and it is great way to use the Ignition Retard functionality in the ECU.