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Boost Control: Boost Control Plumbing

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Boost Control Plumbing


00:00 - Without fail, the most common reason for boost control problems is due to incorrectly plumbed vacuum hoses between the boost pressure source, boost solenoid, and wastegate.
00:12 The preceding modules have laid the groundwork necessary for us to discuss the correct plumbing in this module.
00:19 In order to be able to work through this in a logical manner, we need to first understand how the wastegate functions and secondly understand how the solenoid works.
00:30 If we understand both, this module should seem very logical.
00:35 Before we look at how we can use a three-port solenoid though, I'll just touch on how a two-port solenoid is often incorporated into a factory turbo car, as you may want to retain this type of system in some OE applications.
00:51 These are used exclusively with internal wastegates and they act as a bleed valve to reduce the boost pressure reaching the wastegate actuator.
01:00 Here's a diagram of the connections.
01:03 Remember that with this sort of wastegate, we need to reduce the pressure signal reaching the wastegate in order to raise the boost pressure.
01:12 The pressure source comes from either the turbo compressor or the inlet manifold and is plumbed to a tee piece.
01:19 From here, one hose goes to the wastegate actuator and the other goes to the boost solenoid.
01:26 When the solenoid is closed, it's the same as having the boost pressure connected directly to the wastegate actuator and will achieve minimum boost pressure.
01:36 Energising the solenoid will vent boost pressure away from the wastegate actuator and hence, reduce the pressure in the actuator which will increase the boost.
01:47 The other connections from the solenoid is just to vent the excess air, and this can either vent to atmosphere or be plumbed back into the intake system somewhere before the turbo.
02:00 In order to get a reasonable control range with the system, we'll also need a restrictor in the pressure line coming from the pressure source.
02:09 This is normally a brass olive with a small internal hole that reduces the volume of air reaching the wastegate.
02:17 With the restrictor in place, it means the solenoid is able to vent a larger percentage of the air reaching the wastegate and hence, we can increase the boost further.
02:28 Without a restrictor in line, the turbo can move so much air that it replaces the volume of air in the line almost as quickly as the solenoid can vent it.
02:37 This means we'll have limited control over the boost and won't be able to increase it very far from stock.
02:46 The downside with this sort of system is that some amount of pressure is always reaching the wastegate and this can result in the wastegate beginning to open before we reach our desired boost level.
02:59 We also don't have complete control over the level of pressure reaching the wastegate and hence, this isn't my preference with plumbing an internal wastegate actuator.
03:10 My preferred method of controlling an internal wastegate is with a three-port solenoid plumbed as shown here.
03:18 With the three-port solenoid, we can have complete control over the amount of pressure reaching the wastegate actuator.
03:25 This means we can eliminate any pressure reaching the wastegate while the turbo is spooling up to ensure the wastegate remains 100% closed.
03:35 This technique is well-promoted by just about any aftermarket boost controller manufacturer as offering a huge improvement to boost response.
03:45 The reality is that these gains are usually quite small in most instances, however, it can still be a worthwhile improvement.
03:55 The other advantage to using a three-port solenoid is that the range of boost control we have is also wider since we can vary the boost pressure anywhere from the minimum wastegate spring pressure all the way through to the point where no pressure is reaching the wastegate actuator at all, and the boost pressure will be the maximum amount achievable with a spring fitted to the wastegate.
04:18 With this technique, the common port is connected to the wastegate, and the normally open port is connected to a pressure source.
04:27 The normally closed port is the vent and can be either left open to atmosphere or connected back to the intake pipe pre-turbo.
04:36 When the solenoid isn't energised, the normally open and common ports are connected and hence, boost pressure's connected directly to the wastegate actuator.
04:48 When the solenoid is energised, the common and normally closed ports will be connected which allows the pressure in the wastegate actuator to be released and vent to atmosphere.
04:59 This lets the wastegate close and the boost increase.
05:03 By pulse-width modulating the solenoid, accurate control can be achieved.
05:09 Now we've covered internal wastegates, we'll look at external, or two-port, wastegates.
05:15 There are two common ways of plumbing an external, or two-port, wastegate.
05:19 We can treat them the same as a single-port wastegate and plumb the boost controller as we can see here.
05:26 In this case, we're just leaving the top of the wastegate venting to atmosphere.
05:31 The other option is to connect the wastegate using both ports as shown here.
05:37 This technique leaves the bottom of the wastegate continuously connected to pressure and then uses the solenoid to apply pressure to the top of the wastegate when more boost is required.
05:49 Providing boost to the top of the wastegate has the effect of forcing the valve closed, and this method provides an increase in the usable control range of the boost control system.
06:00 In this configuration, the top of the wastegate is connected to the common port on the solenoid and the normally open port is vented to atmosphere or plumbed back to the intake pipe pre-turbo.
06:14 The normally closed port is then connected to a pressure source.
06:18 This can either be taken from the hose connected to the bottom port of the wastegate via a tee piece or alternatively can provide the solenoid with its own separate pressure source.
06:31 When the solenoid is not energised, the common and normally open ports are connected together, which allows the top of the wastegate to vent to atmosphere, and this gives us the minimum boost pressure achievable.
06:44 When the solenoid is energised, the common and normally closed ports become connected providing boost pressure to the top of the wastegate and hence, increasing boost pressure.
06:56 If you're running a twin turbo engine, then you'll have a wastegate for each turbocharger.
07:02 In this instance, you'll have the choice of running two wastegate solenoids that are controlled by the same output on the ECU or using a single solenoid to control both wastegates.
07:14 I find that with internal wastegates, a single solenoid will get great results but often on a twin turbo installation, dual solenoids are preferable.