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Turbos/Superchargers and vacuum

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  • #637272
    GabbyGabby
    Participant

      Hi, I understand the concepts of turbos and superchargers, but what I’m wondering is, how do vacuum operated things like the brake booster and cruise control and HVAC systems, EGR valves etc all work when there is positive boost?

      Cheers, Gab

    Viewing 7 replies - 1 through 7 (of 7 total)
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    • #637319
      AlexAlex
      Participant

        Many (all?) forced induction vehicles have a separate electric pump to power systems that need vacuum. Diesel engines, turbo or not, require a similar pump because all but a few designs have no throttle butterfly valve and thus no manifold vacuum.
        It might be possible to use check valves and a larger vacuum reservoir in some setups. However it could run out of vacuum if the engine had boost for a while and many devices needed vacuum during that time.

        #637390
        dandan
        Moderator

          have the break booster line before the turbo or where air is drawn in on the blower, air must go in somewhere, and in the process of drawing air in forced induction must also make a vacuum. for example on Turbocharged vehicles the PCV systems lines typically go on a part of the intake before the turbo, as for supercharged engines the PCV line would typically connect at the throttle body or slightly after or some part of the intake before the blower, the PCV positive crankcase ventilation system typically works buy using engine vacuum to help draw out crankcase gasses such as blowbuy at lower revs, and at higher revs letting the pressure in the crankcase push itself out into the intake.

          some diesel engines use hydraulically boosted breaks rather than vacuum, and some racing engines have open valve breathers with filters, that’s why some engines have filters on top of the rocker covers, they don’t have positive crankcase ventilation because they really don’t need it.

          #637399
          James O'HaraJames O’Hara
          Participant

            Most diesel engines (other then autos?) don’t use vacuum they use positive pressure. They are built that way because they do not create vacuum except before the turbo. Like said above they either use a hydraulic brake booster and/or air.

            #637420
            dandan
            Moderator

              some diesel engines can also use a vacuum pump.

              #637544
              James O'HaraJames O’Hara
              Participant

                I am assuming you are talking about Class C autos aka light duty trucks, cars, suvs. In which case I wouldn’t know that much about them using vacuum. It would make sense because it would be cheaper to use vacuum parts they make for other vehicles. As for anything Class A or B like medium duty, heavy duty, construction equipment, and marine I highly doubt they use vacuum as it is just another part to have fail.

                #637659
                dandan
                Moderator

                  its not very common to use a vacuum pump, its more common for them to use means as you have stated.

                  #645186
                  Lorrin BarthLorrin Barth
                  Participant

                    [quote=”Gab250″ post=120580]Hi, I understand the concepts of turbos and superchargers, but what I’m wondering is, how do vacuum operated things like the brake booster and cruise control and HVAC systems, EGR valves etc all work when there is positive boost?

                    Cheers, Gab[/quote]

                    I drive a turbocharged car.

                    The braking system is identical, as near as I can tell, to the braking system on a NA car.

                    The cruise control needs to be electric. A previous car I owned, also turbocharged, came without cruise and I installed a vacuum powered cruise. It worked okay except I could only go so fast and on hills it would slow. As I recall, about 70 mph on the flat was the limit because that was where boost started to come on (at about 3000 rpm).

                    I had a problem with my HVAC system, the blend door was binding – fixed that – it is manually operated – but never checked to see if there are any air motors in the system. I never thought about it till now.

                    The PCV valve connects directly to the intake manifold and seals under pressure. In other words it also acts as a check valve preventing the crankcase from being pressurized to manifold pressure. There is a second port on the valve cover that connects to the intake in order to ventilate the crankcase during boost. It connects after the mass air sensor but before the turbo. Under manifold vacuum crankcase gases are pulled through the PCV valve to be replaced by filtered air pulled from the intake by way of the second hose. During boost only the second line is open.

                    Another interesting feature is the fuel pressure regulator. Since the intake manifold may contain either vacuum or pressure the fuel pressure regulator has the ability to handle both in order to keep a steady manifold to fuel pressure difference. I’m too ignorant to know if this requires a special type of regulator or if a regulator off of a NA car would suffice.

                    The EGR works off of vacuum but has an electric solenoid controlled by the ECU. Just exactly when it is open is an interesting question.

                    My car, a 2003 Evo, came from the factory developing 280 hp on 2 liters at about 21 psi maximum boost. Back then it was – that will blow up. I was amused to see the new last year Cadillac ATS with the same sized turbo engine finally developing nearly the same horse power. Now, the Evo is built to be hammered on by kids and runs very rich in stock form so not economical. But the Cadillac I saw on the lot had a manual transmission and AWD. It was even painted red like the Rally Red on my car. It was an Evo in Cadillac form. This year I notice the manual has been dropped – I guess it didn’t sell. Too bad but that is America.

                    What Ford is doing with their trucks is truly amazing. I hope it works out for them. It appears the boosted stuff in smaller vehicles is working and advancing.

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