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Launch Control: E-Throttle Control

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E-Throttle Control


00:00 - While controlling the rev limit relative to ground speed is an effective way of modulating engine power, if your engine is equipped with an electronic throttle and you have a capable ECU, then you can also control the throttle opening.
00:14 This technique sounds ideal and obviously, it can be very powerful. However, in practice, I find it can be difficult to get really good results if you rely solely on the E-throttle.
00:25 Theoretically, what we could do is go out and perform a number of launches in the car, manually controlling the amount of wheel spin by modulating the throttle.
00:35 Once you've achieved a launch that you consider to be near-perfect, you can then look at the data log and recreate the throttle opening you used in the launch control table.
00:45 In practice, I find this technique to be less successful than a simple rev limiter on its own though.
00:50 The problem with this technique is that modulating the throttle offers what I'd consider a coarse control of the engine power.
00:58 That might sound a little backwards so let me explain further.
01:01 Obviously, by moving the throttle we have infinite control over the engine power.
01:07 When we're manually launching the car with no launch control we'll automatically manipulate the throttle to control the amount of wheel spin, and as we've discussed already, the aim is to maintain a small amount of wheel spin.
01:20 If we close the throttle too far, the tires can grip and drag the RPM down, bogging the car.
01:27 If we're manually controlling the throttle, we can add more throttle to increase the power and prevent this, however, the launch control system doesn't use feedback.
01:36 It simply does the same thing it was programmed to do every time.
01:40 And if our throttle target is too close to what we need to maintain a good launch, it's quite possible to end up with the engine falling off power and bogging.
01:50 In comparison with controlling the engine rev limit, the ECU can actively change the percentage of cut being applied as required to suit the amount of engine power being produced.
02:02 Now this isn't to say that manipulating the throttle opening is completely pointless though.
02:07 Particularly on very powerful cars, it can be beneficial to use throttle control to reduce the engine power somewhat and this means that ECU won't need to rely so heavily on the rev limit to achieve good control.
02:21 Rather than trying to program a table of wildly varying throttle position relative to ground speed which is what we might end up doing when launching the car manually, if I'm going to employ throttle control, I'll use the table to reduce the throttle position by a set amount throughout the launch.
02:40 This might mean that when the driver is at a 100% throttle on the pedal, we only give the engine 70% throttle opening.
02:48 That's also with smoothly increasing this value back to 100% near the end of your launch control table, so the transition to full engine power is smooth when you exit launch control.
02:59 I'll only generally apply throttle control on very powerful cars or perhaps as a wet weather launch setting.
03:06 My technique is to start by tuning the rev limiter settings as we've already discussed.
03:12 Once you have this table dialed in, you can try reducing the throttle opening in 10% increments and logging the result.
03:19 If you go too far, you'll find that the car may begin bogging during launch and in this case I'd add 10 to 15% throttle back into the table and try again.
03:31 With a properly tuned throttle target table, the ECU won't be relying so much on the rev limit to control the engine power and you may find that the engine sounds cleaner and feels smoother.
03:43 One last tip is that you may still get a better result if you're targeting 100% throttle when the car's stationary.
03:50 This will be essential on larger turbos to allow a sufficient boost to be produced.

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