Help me understand how a turbo and boost controller works?

[NickF509]

Okay i've read plenty of basics videos and watched a few movies on how a turbo works and i'm pretty sure I've had a good idea for awhile but I want to see if you guys could help me check my understanding.

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I borrowed this setup picture to help with this conversation. Below is what I understand to this point, please let me know if I am correct.

1) The car is at a stop and the gas is pressed for it to start accelerating. Air moves throw the intake, gets seen by the air flow meter (what is the point of the air flow meter?) and moves into the engine, it the gets compressed fuel is added and a spark is made causing the piston to move causing power to be generated. Exhaust is made from this. The exhaust moves over the turbine wheel and causes it to start spinning.

2) This in turn causes the compressor wheel to spin which starts forcing more air or "Boost" into the engine which allows for more fuel to be added which allows for more power to be made which allows for more exhaust to be generated which allows for more air to be forced into the engine.

3) The wastegate actuator is controlled by the boost controller so that at a given amount of pressure it opens the wastegate and allows the exhaust to vent past the turbine wheel which decreases the amount of turbine spin being created which reduces the amount of compressor spin which reduces the amount of forced air (boost) being made.

4) The car rapidly decelerates which causes something that causes it to need to vent air via the blow off valve. I don't really understand this process.

I also do not understand what the tubes marked 1. and 2. are for.

1. seems like it would be to detect the amount of air pressure before going through the intercooler and 2. seems like it would be to detect the amount of air pressure after the intercooler but I don't understanding the reasoning for this?

Sorry for the long post and thank you for any help you can give understanding this process.

 

[TSITurbo95]

From this diagram (not related to dsm's) but #1 tube is to measure the pressure before the throttle plate, and #2 is to measure the pressure after the throttle plate. Also, all inter coolers have a pressure drop of some sort. As all turbo systems, the PSI will differ from inter cooler pipes and intake manifold.

 

[92AWDHX40]

http://www.dsmtuners.com/forums/art...ost-control-wastegates-how-turn-up-boost.html

 

[PotatoFlakeSTi]

Regarding point 4 specifically;

When you let off your accelerator, the plate in the throttle-body closes.
This creates a large amount of pressure in your piping, which will violently stop your turbo, to prevent damage to the turbo, and to prevent the turbo from spinning backward or coming to a stop, a Bypass Valve or Blow Off Valve is used to vent the positive pressure.

 

[Junfan]

Now that you understand how the BOV works remember if you want you car to run better recirc your BOV. If you do not you are letting metered air of the system and running pig rich for a second and can stall your car if under WOT just as you push the clutch in. The air will reenter the air system just after the MAS as not to be measure twice.

 

[NickF509]

Regarding point 4 specifically;

When you let off your accelerator, the plate in the throttle-body closes.
This creates a large amount of pressure in your piping, which will violently stop your turbo, to prevent damage to the turbo, and to prevent the turbo from spinning backward or coming to a stop, a Bypass Valve or Blow Off Valve is used to vent to positive pressure.

How does the BOV or Bypass Valve know to open?

Now that you understand how the BOV works remember if you want you car to run better recirc your BOV. If you do not you are letting metered air of the system and running pig rich for a second and can stall your car if under WOT just as you push the clutch in. The air will reenter the air system just after the MAS as not to be measure twice.

Ahh that makes sense I couldn't quite understand why everyone always said to recirc the BOV.

 

[90_eclipse]

The purpose of the Air Flow Meter (AKA MAF or MAS) is to measure the amount of air the comes into the engine. The ECU uses this measurement of air to release a measurement of fuel through the fuel injectors (So Basically, fuel is the controlled substance in relation to incoming air. Fuel is added depending on the amount of air, measured in Hz frequencies, passing through the MAF). Our MAF is a Karmen Vortex style MAF. It measures the volume of air by calculating the "distrubances" in air flow through the honey combs.

sourced from K&N...
"An older style of AFM still in limited use, the Karman Vortex air flow meter uses an air stream-centered conical vortex generator to create vortices, essentially precisely-shaped air disturbances, in the measurement chamber. First, however, the air stream passes through a honeycomb grid to straighten airflow and reduce turbulence.

Located on either side of the chamber of one type of vortex meter are a transmitter and receiver that send and receive a signal, either infrared light or ultrasonic waves. The amount of distortion in signal caused by the vortices, whose frequency increases with airflow, is measured and compared against a known set data points, from which an inference about air flow is made.

Another type of Karman Vortex Meter features a pressured directing hole in which sits a metal foil mirror which oscillates in proportion to the vortex frequency. The movement of the mirror deflects light from an LED on and off of a photo transistor or diode, opening and closing a 5-volt loop to generate a signal. Air flow, combined with a temperature reading from an internal sensor, is used to generate a measurement of air mass."


Most BOVs open through pressure sensoring... the same way a wastegate knows when to open. An exception to this is the HKS SSQV I believe. A tensioner screw is added to adjustable BOV's to open depending on a certain PSI.

 

[blkgst97]

How does the BOV or Bypass Valve know to open?
.

While under boost the line going from the intake manifold to the blow off valve is supplying pressure to help keep the bov closed. When the throttle plate closes it creates vacuum behind it. the line going to the bov now does not have pressure keeping it closed. The positive pressure still be creating in the intake pipe now over comes the spring pressure in the blow off valve and releases.

 

[LiquidX]

If you look at the BOV, it's bolted to the intercooler piping which sees positive pressure. There is a vacuum line that goes from the body of the BOV to the intake manifold. What happens is when the throttle plate closes, you have positive pressure (due to the turbo) in the IC pipe, and the intake manifold is now in a vacuum since the motor is still sucking in air.

So, you have positive pressure pushing up underneath the BOV and vacuum pressure pulling open the BOV. When ever there is enough of a difference between the 2 halves (separated by a diaphragm) the valve will open. There is an internal spring to help keep the valve closed in times that it shouldn't be open (idle).