ALL BOOST CONTROL setups EXPLAINED - Boost School #3

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Welcome back to Boost School! Today we're talking about something that is as important as boost itself, and that something is control and we will cover all the boost control setups, starting with the most basic level 1 setup and proceeding to the most complex and performance oriented level.
LEVEL 1 BOOST CONTROL - wastegate + wastegate actuator
The most basic setup consists of nothing but your wastegate and your wastegate actuator. This simple setup works by having a boost reference line connected to a boost source. Boost pressure is exerted onto the spring and diaphragm inside the wastegate actuator. Once boost pressure gets high enough it compresses the spring and opens the wastegate. Having quick turbo spool up with this setup is next to impossible as the spring inside the actuator is exposed to boost pressure all the time. Your wastegate will be fully opened when you hit the boost the spring is rated for, but your wastegate will actually start to open way sooner than target boost.
LEVEL 2 BOOST CONTROL - manual boost controller
A manual boost controller will alloy you to make boost than your spring would allow by delaying the boost going through the reference line. Inside a manual boost controller is a spring and a ball. Adjusting a knob or turning the controller itself will change the spring pressure on the ball. Lifting the ball up from it's seat will require more boost pressure than compressing the wastegate spring so your turbocharger generates more boost. Although the manual boost controller is very simple to install and increases boost pressure it doesn't do anything else. It's dumb just like the level 1 setup and references nothing other than boost. It has no idea about your throttle opening, intake air temperature etc. which can result in full boost at half throttle or a setting that needs readjustment for different weather or or altitude.
LEVEL 3 BOOST CONTROL - 2 port boost control solenoid
The simplest electronic setup involves a 2 port boost control solenoid. The 2 port solenoid is connected into the boost reference line with a T fitting and it bleeds boost pressure from the line between the turbo and wastegate actuator. Essentially the 2 port boost solenoid is lying to the spring in the wastegate actuator by making it "think" there's less boost being made than actually is. The great advantage between a 2 port boost solenoid and any manual boost controller is that the solenoid is connected to the ECU and the ECU can manipulate the solenoid's duty cycle based on throttle opening, air temperature, coolant temperature, etc. so you'll never get full boost at half throttle again. The downside is that with the 2 port solenoid and the t-fitting the spring still sees boost pressure all the time so the 2 port solenoid still can't prevent it from being slightly opened before it needs to be.
LEVEL 4 BOOST CONTROL - 3 port boost control solenoid
Unlike the 2 port solenoid which is installed with a t-fitting, the 3 port boost control solenoid is installed directly into the boost reference line and it interrupts the boost pressure going from the turbo to the wategate actuator. Because it has one more port the 3 port boost solenoid can control boost more accurately and with less duty cycle compared to a 2 port solenoid resulting in better turbo responsiveness, quicker spool up and more power, as well as more headroom to increase boost later on.
LEVEL 5 BOOST CONTROL - 3 port boost control solenoid + external wastegate
When hooked up to an external wastegate a three port solenoid can be used to direct boost pressure to the top port of a two port wastegate helping reinforce the spring and keeping it closed. This is a superior setup to "lying to the spring" and it results in even better turbo responsiveness and more aggressive spool up.
LEVEL 6 BOOST CONTROL - 4 port boost control solenoid / 2 X 3 port solenoids
The 4 port boost control solenoid can do something a 3 port cant'. It can control the top and bottom of a 2 port external wastegate at the same time. A 3 port solenoid can make twice the boost pressure of your base spring, but a 4 port solenoid can make 5-6 times that which means it's capable of generating some extreme boost. The only real downside is poor resolution. Changing a 4 port solenoid duty cycle by just 1-2% can result in 3-8 psi of boost pressure change. To correct a bumpy boost curve generated by a 4 port solenoid you can use two 3 port solenoids, but this will require a very capable ECU and some pretty complex tuning.
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