Question about variable vane turbochargers.

[454Casull]

Does the backpressure remain constant throughout the boost range? i.e. does the engine feel a greater backload at high boost than at low boost?

To me, it seems as if the high degree of redirection at high boost presents an impediment to the exhaust gases.

Sorry for the crappy vocabulary, I had a bad day.

[SaabJohan]

Exhaust pressure does always increase with increasing boost pressure, this is because the boost pressure, or more correct pressure ratio and massflow will dictate the amount of power needed from the turbine, and since increased flow also means increased exhaust flow we can se that the pressure ratio over the turbine and compressor are related, simplified, only affected by exhaust enthalpi and efficiencies.

However, the VNT technology can by changing the turbine nozzle area adjust the speed of the gases that flows into the turbine, and this makes it possible to reduce exhaust pressure at high rpm's as well as lower the boost threshold and reducing lag.

[454Casull]

Originally Posted by SaabJohan

Exhaust pressure does always increase with increasing boost pressure, this is because the boost pressure, or more correct pressure ratio and massflow will dictate the amount of power needed from the turbine, and since increased flow also means increased exhaust flow we can se that the pressure ratio over the turbine and compressor are related, simplified, only affected by exhaust enthalpi and efficiencies.

However, the VNT technology can by changing the turbine nozzle area adjust the speed of the gases that flows into the turbine, and this makes it possible to reduce exhaust pressure at high rpm's as well as lower the boost threshold and reducing lag.

Are we talking about the turbine that changes the area of the entry with vanes?

[SaabJohan]

Originally Posted by 454Casull

Are we talking about the turbine that changes the area of the entry with vanes?

Are there any other type?

[454Casull]

Originally Posted by SaabJohan

Are there any other type?

I don't know, I wasn't too sure.