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Thread: Turbos

  1. #11
    Off the Xmas card list kapri's Avatar
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    There is on tickover and cruising revs ,even on blow through ? Least there is on my vacuum gauge Once it starts to make boost at high revs it should balance out though? Or is it too late and I should really go to bed ?

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    Got salt Briz's Avatar
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    I'm not well versed, but I cant see how given that the inlet is effectively open to atmosphere. Unless the air filter is a bit restrictive....

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    TechnicalTom
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    Quote Originally Posted by kapri View Post
    There is on tickover and cruising revs ,even on blow through ? Least there is on my vacuum gauge Once it starts to make boost at high revs it should balance out though? Or is it too late and I should really go to bed ?
    I am of the same opinion here,off boost there is a vacuum , most probably high vacuum on overun as well .
    I have tried using a Holset diesel turbo on a 1600 Fiat twin cam engine. the Turbo was brand new at the time.Lots of smoke a bit like the vapor trail on the Red Arrows .That was a blow through set up .

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    TechnicalTom
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    Quote Originally Posted by Briz View Post
    I'm not well versed, but I cant see how given that the inlet is effectively open to atmosphere. Unless the air filter is a bit restrictive....
    Just put your hand over the inlet pipe and you will see just how much vacuum is present.( with the engine running)

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    Got salt Briz's Avatar
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    I'm not getting this; sure, theres always air demand and if you put your hand over the inlet a vacuum is then formed as you've made a restriction.
    Put your hand over a diesel inlet and you'll feel a vacuum too!
    Vacuum is surely only present between the throttle butterfly and the engine, especially, as you say, on overrun - when there is always maximum vacuum.
    But upstream of the throttle, conditions must be the same as on the diesel application.

  8. #16
    Official RnS Addict scooder's Avatar
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    Intresting. Carry on.
    Thanks
    Martin.

  9. #17
    Off the Xmas card list kapri's Avatar
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    Quote Originally Posted by Briz View Post
    I'm not getting this; sure, theres always air demand and if you put your hand over the inlet a vacuum is then formed as you've made a restriction.
    Put your hand over a diesel inlet and you'll feel a vacuum too!
    Vacuum is surely only present between the throttle butterfly and the engine, especially, as you say, on overrun - when there is always maximum vacuum.
    But upstream of the throttle, conditions must be the same as on the diesel application.
    Isn't that just airflow though Briz ( if so means you are correct re no vacuum upstream of throttle restriction) ?

    Vacuum is caused by the restriction of airflow into the engine by the throttle butterfly so vacuum below the throttle plate is available until wide open when pressure vs vacuum equalises as it becomes just an open orifice.


    What I don't understand is why you don't get vacuum on a diesel ( to work brakes ) if putting your hand over the air inlet 'sucks'? I know the revs are fuel volume controlled 'by the pump' rather than by fuel controlled 'by airflow' .However if no airflow then what helps the diesel to explode ? If air isn't required then why have an 'air volume' flap ( what I see as a carb butterfly ) ?

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    Got salt Briz's Avatar
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    Yeah Kev. I think you've answered your own question.

    "Vacuum is caused by the restriction of airflow into the engine by the throttle butterfly so vacuum below the throttle plate is available until wide open when pressure vs vacuum equalises as it becomes just an open orifice."

    So with no throttle valve, the diesel if effectively at full throttle all the time. Plenty of airflow, but no restriction so therefore no vacuum.
    Same as a petrol engine at WOT.

  11. #19
    Official RnS Addict scooder's Avatar
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    Could you not change the seals?
    Martin.

  12. #20
    Turbo 4 pot freak 20vT_pop's Avatar
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    Kev on the original Sherpa diesels they had a ridiculas throttle butterfly unit with a vacuum unit and 2 x butterflys and several different adjustments which was a pain in the arse to set up so it didn't smoke and supplied enough vacuum for the servo. It wasn't long before they came out with the vacuum pump on them. Because with diesels all you are doing is adding atomised fuel, the more fuel in the right quantities the more power and higher revs.

    John
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    Anyone can drive a fast car, not everyone can drive a car fast!!!!

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