This discussion is nothing new, but something I think is missing from this forum. Many who come on here understand what a turbo is and what a turbo does but not everyone may know how it works, the different parts, and what these parts look like. While turbo models vary and where their parts are located are different, they all have these same parts to do the same jobs. So realize that the way these parts look on different setups may not be the same, but they will operate the same way and have the same job.
On that note however, keep in mind when we discuss valves in the turbo, there are two different types, recirculating and atmospheric. Recirculating valves will take whatever airflow they are controlling and recirculate it back into the system. Atmospheric will take the airflow and vent it out to the atmosphere. As a matter of fact, a Blow Off Valve and a Bypass Valve are the same thing with the only difference being a Blow Off Valve vents to atmosphere while a Bypass Valve recirculates. In the K04, all the valves are recirculating systems and all OEM turbos (at least all the ones I've seen in cars since 1992) are this way for smog reasons.
Let's start with a picture of the K04 assembled and the different components of it.
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Thanks to Jgasser, I was able to document a disassembled K04 and take these pictures. This turbo wore out and needs to be rebuilt but if you just looked at these pictures you may not realize it. This first picture shows the center section of the turbo. This is the heart of the turbo. This includes the compressor fan, turbine fan, turbo shaft, and the oil and water passages used to lubricate and cool the turbo shaft and it's bearings. Hence on this part you will find all the oil and water line ports.
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In this picture the turbine fan is on the right and the compressor fan on the left. The turbo shaft connects these two through the center of this part.
The turbine fan's blades are curved to meet the incoming flow of exhaust and use it's energy to spin up the fan. Here is a picture of the turbine fan and the housing that it goes into on the turbo body. (note the housing is in the distance, hence why it looks like the fan is too big to fit in the housing)
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This spins the turbo shaft and, with the compressor fan attached to the same shaft, turns the compressor fan. This fan also has curved blades to catch the incoming air, compress it, and force it out the turbo's outlet. Below is a picture of the compressor fan and housing.
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The concept behind these components is pretty easy to understand and is the part most people know about when it comes to turbos. The more exhaust gases move into the turbine housing, the faster the fan spins the shaft. The faster the shaft spins, the faster the compressor fan spins. The faster the compressor fan spins, the more boost is produced in the compressor housing and delivered to the engine.
What is less understood is the amount of boost a turbo can make, the amount it should make, and controlling the amount you want it to make. To understand how this works and why it needs to work you have to understand a couple of general ideas about compressing air.
When you compress air, you also are heating the air. As air compresses it gets hotter and while the pressure of the air will go up, it's density will go down. This presents means the two are a bit counter productive. We're compressing air to get more air in the engine per revolution but hot air is less dense and thus the hotter air charge has less air in it at a given pressure than a colder air charge at the same pressure. This is what we have intercoolers for. Because of this fact, a turbo has a certain range of boost it can generate effectively without the heat that boost range generates overcoming the amount of air the boost level it is generating delivers.
For instance, say a turbo flows 30,000 cfm of air at 23 psi of boost, the upper limit of it's boost map. If you push that turbo to 24 psi, the cfm generated drops to 29,000. 25 psi and it drops to 27,000...and so on. That's called running a turbo off it's map.
The K04 turbo can generate more than 25 psi of boost but on the LNF, running more boost than that is running it off it's map. If left uncontrolled, the turbo would regularly exceed 24 psi of boost generating unnecessary heat and cause detonation in the engine. To prevent this from happening, turbos are equipped with a wastegate. Many times people confuse the wastegate with the blow-off or bypass valve...the valve that makes that signature PSSST sound on a turbo car when you let off the gas after accelerating really hard. The wastegate controls the amount of exhaust that is allowed to move through the turbine and drive the turbo.
When the boost level of the turbo reaches where the system designer wants it, the wastegate begins to open (which is done mechanically with the wastegate actuator) allowing some of the exhaust gases to bypass the turbine and go directly to the exhaust outlet. This limits how much energy is driving the turbine to a level where the turbo will only produce a certain level of boost. Here is the integrated recirculating wastegate valve in the K04 in the closed position. The studs you see in this picture are the studs that connect the catalytic converter to the turbo housing.
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On that note however, keep in mind when we discuss valves in the turbo, there are two different types, recirculating and atmospheric. Recirculating valves will take whatever airflow they are controlling and recirculate it back into the system. Atmospheric will take the airflow and vent it out to the atmosphere. As a matter of fact, a Blow Off Valve and a Bypass Valve are the same thing with the only difference being a Blow Off Valve vents to atmosphere while a Bypass Valve recirculates. In the K04, all the valves are recirculating systems and all OEM turbos (at least all the ones I've seen in cars since 1992) are this way for smog reasons.
Let's start with a picture of the K04 assembled and the different components of it.
Thanks to Jgasser, I was able to document a disassembled K04 and take these pictures. This turbo wore out and needs to be rebuilt but if you just looked at these pictures you may not realize it. This first picture shows the center section of the turbo. This is the heart of the turbo. This includes the compressor fan, turbine fan, turbo shaft, and the oil and water passages used to lubricate and cool the turbo shaft and it's bearings. Hence on this part you will find all the oil and water line ports.
In this picture the turbine fan is on the right and the compressor fan on the left. The turbo shaft connects these two through the center of this part.
The turbine fan's blades are curved to meet the incoming flow of exhaust and use it's energy to spin up the fan. Here is a picture of the turbine fan and the housing that it goes into on the turbo body. (note the housing is in the distance, hence why it looks like the fan is too big to fit in the housing)
This spins the turbo shaft and, with the compressor fan attached to the same shaft, turns the compressor fan. This fan also has curved blades to catch the incoming air, compress it, and force it out the turbo's outlet. Below is a picture of the compressor fan and housing.
The concept behind these components is pretty easy to understand and is the part most people know about when it comes to turbos. The more exhaust gases move into the turbine housing, the faster the fan spins the shaft. The faster the shaft spins, the faster the compressor fan spins. The faster the compressor fan spins, the more boost is produced in the compressor housing and delivered to the engine.
What is less understood is the amount of boost a turbo can make, the amount it should make, and controlling the amount you want it to make. To understand how this works and why it needs to work you have to understand a couple of general ideas about compressing air.
When you compress air, you also are heating the air. As air compresses it gets hotter and while the pressure of the air will go up, it's density will go down. This presents means the two are a bit counter productive. We're compressing air to get more air in the engine per revolution but hot air is less dense and thus the hotter air charge has less air in it at a given pressure than a colder air charge at the same pressure. This is what we have intercoolers for. Because of this fact, a turbo has a certain range of boost it can generate effectively without the heat that boost range generates overcoming the amount of air the boost level it is generating delivers.
For instance, say a turbo flows 30,000 cfm of air at 23 psi of boost, the upper limit of it's boost map. If you push that turbo to 24 psi, the cfm generated drops to 29,000. 25 psi and it drops to 27,000...and so on. That's called running a turbo off it's map.
The K04 turbo can generate more than 25 psi of boost but on the LNF, running more boost than that is running it off it's map. If left uncontrolled, the turbo would regularly exceed 24 psi of boost generating unnecessary heat and cause detonation in the engine. To prevent this from happening, turbos are equipped with a wastegate. Many times people confuse the wastegate with the blow-off or bypass valve...the valve that makes that signature PSSST sound on a turbo car when you let off the gas after accelerating really hard. The wastegate controls the amount of exhaust that is allowed to move through the turbine and drive the turbo.
When the boost level of the turbo reaches where the system designer wants it, the wastegate begins to open (which is done mechanically with the wastegate actuator) allowing some of the exhaust gases to bypass the turbine and go directly to the exhaust outlet. This limits how much energy is driving the turbine to a level where the turbo will only produce a certain level of boost. Here is the integrated recirculating wastegate valve in the K04 in the closed position. The studs you see in this picture are the studs that connect the catalytic converter to the turbo housing.
