Hi,
When MOTing a car now a diesel car is revved up to 6 times at governed limit of the engine.
We are discussing now is it is wise to rev a turbo charged engine to full governed limit off load.
Can anyone advise if this is good recommended practice or frowned upon from car manufacturers?
Hope I dont open a can of worms with this one.
Thanks
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Won't do it ny harm if it's up to temperature, in fact off load the turbo will barely spin up as it needs a load to function.
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I hate that test. It always sounds like the engine is going to let go. Some manufacturers detect the bonnet is open and that the vehicle is not moving and limit the max revs via the ECU, still don't like it though. P.S. A turbo spins becuase of the volume of exhaust gas going thru it and does not need a load. Regards Peter
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Is it a lot worse for the engine to do it without load then?
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On the grounds that the piston can accelerate faster with no crankshaft load then it must rattle thinks a bit harder. Regards Peter
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On full throttle-no-load,I doubt if the turbo goes over 25,000rpm.At full throttle-full-load,it will go to 100,000-125,000rpm..
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Thats the whole point, off load very little gases going through it. On the ALfa you could get a good whistle going by booting it under load, off load you could barely hear it. Same applies to petrols as well.
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Its not a bad idea to rev the nuts off the 306 td one a week anyway, helps clear it out a bit and makes a noticeable improvement too. Certainly aint going to blow up - its limited for a reason.
Also when neutral I cant hear a turbo spinning when revving its nuts off past 2500rpm , which is where it makes a difference.
As mentioned, car ECU realises its at rest, so puts in enough fuel to get it to max limiter without even producing enough exhaust gas to trigger the turbo.
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If there's no load on the engine, then the wastegate diverts the exhaust gas away from the turbo. Otherwise I suspect the engine would have very strange driving characteristics (such as continued boost at high revs on the overrun). I believe the variable vane turbos can do without a wastegate.
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More of a worry would be if cambelt gave in on the test,reason why a warning notice is displayed at testing stations, ie if not changed at correct intervals-failure could occur.
Nothing to do with turbo which should be fine during the test!
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Steve
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If the engine is under load, surely it produces more exhaust gas as it is working harder, therefore the turbo will be spinning more, especially around the 2500rpm mark. When the engine has the nuts revved off it whilst the car is stationary, it isn't under load and so less exhaust gas will be produced I would have thought.
Martin
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Turbo is working whether under load or not,turbo starts just above tickover around 1000rpm or less, only need an exhaust leak after turbo to notice it,ie whistle is very pronounced,it may not be doing anything at this rpm but it still works
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Steve
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