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3 port boost solenoid operation

Boost Control

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Hi all,

Struggling a bit to understand/visualize the operation of a 3 port solenoid when the solenoid is energized.

Lets consider the situation where the waste gate is of the internal type with only one port. Boost pressure is supplied to the common port and goes to the waste gate via the normally open port. The engine will see the minimum boost governed by the spring pressure.

Now lets consider the solenoid is being pulsed at some arbitrary duty cycle, from what I understand, the common and normally closed ports are now connected..but what happen to the normally open port? Is that now 100% disconnected from the common? If so then boost pressure is essentially being bled off from the common port through the normally closed port.... I'm struggling to understand how this affects the actual waste gate actuator if the normally open port is now completely isolated?

Some clarification would be appreciated.

3 port on an internal gate is normally plumbed like below. The common port (usually port 2) is connected to the gate. The NO port (port 3) is connected to the pressure source. The NC port (port 1) is vented to atmosphere.

With no DC on the solenoid then pressure will go straight from the source to the gate (you will be running at spring pressure).

With 100% DC on the solenoid the pressure source will be vented direct to atmosphere and the gate diaphragm will see no pressure (boost will be limited only by EMAP pushing the flap open).

At say 50% DC then half of your pressure source will be dumped to atmosphere and half will go to the gate, so pressure on the gate diaphragm will be at some level below the boost level - hence boost will increase compared to the 0% DC scenario.

Adam, thanks for that. Seems i mixed up the ports in my earlier post.

What's tripping me up still is that in the boost control course, Andre says an advantage of the 3 port over factory 2 port systems is the fact with a 2 port we always have some pressure reaching the gate hence it can begin opening before our target boost is reached. He says with a 3 port, you can eliminates this by ensuring no pressure goes to the gate while the turbo is spooling and that this a technique well promoted by the aftermarket. Is he referring here to running the 3 port at 100% DC while the turbo is spooling? From the way he describes it, it makes it sound like this is an advantage off the bat of the 3 port even if you're running 0 DC and on spring pressure.

Tutors? Anyone ?

Yeah, you can energize the boost control solenoid to prevent the wastegate from opening early.

But I think that @ 100% DC, the pressure source (port 3) is actually blocked and the wastegate port is vented to atmosphere (port 1 and 2 connected together).

Also, on a MAF equipped car, you can recirculate port 1 pre-turbo (between MAF and turbo) to ensure no metered air is vented to atmosphere.