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jx2mad
26th November 2015, 07:27 PM
I have one of these vehicles for work. 308,000k on the clock and still running well. My question is about turbo operation. I know that exhaust gasses spin the turbo to generate boost on the air intake (2l.8l diesel). But what I don't understand is this. Driving at 80k/h in 5th my tacho reads 2.25k revs and the boost gauge is reading 2. If I am stationary and I increase the revs to 2.25k my boost shows zero. Surely in both cases the amount of exhaust gas would be the same because of the same revs, therefore shouldnt the boost be the same? Sorry for the rambling. Jim

justinc
26th November 2015, 08:41 PM
Its the heat energy in the exhaust gasses that drive the turbine . No load = no work = less heat out at the same revolutions.

Jc

jx2mad
27th November 2015, 07:29 AM
If the turbine is spun by the airflow volume and speed surely it would not make any difference if the air was hot or cold.

bee utey
27th November 2015, 08:16 AM
If the turbine is spun by the airflow volume and speed surely it would not make any difference if the air was hot or cold.
I think you've forgotten about one important variable: the fuel that's being burnt. Fast idle = small amount of fuel burnt = small explosions. Cruising = bigger amount of fuel burnt = bigger explosions. The only way you can make air flow in equal air flow out through the turbine is to drive with your foot right off the accelerator. Hot gas from bigger explosions expands via the turbine, cools and transfers energy to the intake turbine. This increases the input flow, allowing more fuel to be burnt cleanly, ergo more output flow, until you hit the wastegate or the limits of the turbo. Exhaust gas typically cools by around 100C across a working turbo. The exhaust gas pressure drops with the temperature as the gas expands inside the turbine.

jx2mad
27th November 2015, 09:26 AM
Thanks,, I bow to superior knowledge. Jim :D:D