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Launch Control: Controlling Boost During Launch

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Controlling Boost During Launch


00:00 - While ignition retard is very effective in producing boost whilst stationary, ultimately, at some point, the wastegate will end up opening, and this can limit the boost pressure you can achieve.
00:10 If you're finding that you can't achieve sufficient boost, even with more ignition retard, it may be that the wastegate is opening earlier than you want it to.
00:19 This is something that's caught me out on a few occasions, so it's important to keep in mind.
00:25 Depending on your ECU's capability, you may have the option to target a specific boost level while the launch control is active, or, alternatively, you may need to modify the base duty cycle table being applied to the wastegate when the car's stationary.
00:41 Since this sort of launch control is usually used in a high-powered engine for drag racing or similar, I usually set up the wastegate base duty cycle table based off either gear or road speed.
00:53 This allows me to independently control the wastegate when the car is stationary, and the launch control's active.
01:00 If you think the wastegate may be opening, it's easy enough to try a large increase in the wastegate duty cycle, and see how that affects the boost pressure.
01:10 If the wastegate has been opening early, this should quickly show an increase in boost, letting you know you're on the right track.
01:17 From here, you can manipulate the table values to achieve your desired boost level.
01:23 If we need to use a lot of ignition retard, you'll often see the boost pressure move around quite a lot due to the pressure pulsations in the exhaust manifold.
01:33 A technique I use on some ECUs to help stabilize the boost is to set up the ignition retard relative to manifold pressure.
01:41 What we find is that, as the turbo begins to create boost, the exhaust flow from the engine will also tend to increase, which, in turn, drives the turbo harder.
01:51 This can result in the boost rapidly rising on the two step.
01:55 Basically, the amount of retard we need to get the turbo spooled up, is not the same as the amount of retard we may need to keep it at our target boost.
02:04 If we set up the ignition retard relative to boost, we can retard the timing aggressively, initially, to quickly build boost from 100 kPa, or atmospheric pressure, and then gradually reduce the amount of retard as we get to our desired boost level.
02:21 As usual, this needs to be set up via testing and data-logging, and we'll look at how this works in some of our worked examples.