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    Vacuum gauges

    Does anyone use a vacuum gauge for engine performance?

    TIA
    Midnight Star
    1996 3587
    Twin diesels, Hino 250's
    Ladysmith, BC
    History: 1996 - 2655, 2001 - 2855, 1984 - 3270

    #2
    Originally posted by freedre View Post
    Does anyone use a vacuum gauge for engine performance?

    TIA
    On gasoline engines - yes.
    Northport NY

    Comment


      #3
      Originally posted by Smitty
      On gasoline engines - yes.
      Other than when adjusting a carburetor's low speed circuits (at idle speed while in neutral), a vacuum gauge connected to a gasoline marine engine will serve no purpose.

      Once the engine begins to move the hull, the engine is under load.
      That load never ends, no matter what speed we cruise at.
      The position of the throttle plates (while under load) drastically lowers manifold pressure that the vacuum gauge would otherwise be reading.

      Now, on a gasoline car or truck engine that can see variable "easy load time", yes..... it would be helpful.




      Edited to add quote by Smitty.
      Last edited by 2850Bounty; 08-21-2021, 03:49 AM.
      Rick E. Gresham, Oregon
      2850 Bounty Sedan Flybridge model
      Twin 280 HP 5.7's w/ Closed Cooling
      Volvo Penta DuoProp Drives
      Kohler 4 CZ Gen Set

      Comment


      • freedre
        freedre commented
        Editing a comment
        Thanks Rick

      #4
      ^^ That is complete BS. There are tons of reasons to have a vacuum guage. With my fuel injected setup, I display manifold pressure, which is just the flip side of vacuum.

      Usually it's primary purpose is that it can be used as a measure of engine loading. If you know the typical idling vacuum and you detect a change or needle bounce you can detect all kinds of things from a vacuum leak to a misfire.

      You can use the guage and a speedo to determine your optimally efficient point of cruise...

      You can use it to determine when it's time to clean your hull...


      The list is kinda endless.


      Chay

      Comment


        #5
        I agree that vacuum gauges are a valuable tool to measure engine performance, however it is almost a lost art on how to use one. Most trouble shooting now days relie on searching for fault code when sometimes we need to get back to basics.
        2003 245 5.0L Alph 1 Gen II
        Libertyville IL.

        Comment


          #6
          .........
          Originally posted by cfoss View Post
          ^^ That is complete BS. There are tons of reasons to have a vacuum guage.
          OK Buddy.... roll up your sleeves, put on your heavy gloves, and get ready for a friendly and adult type debate.

          Click image for larger version  Name:	boxing ring cartoon.jpg Views:	0 Size:	177.8 KB ID:	629584


          With my fuel injected setup, I display manifold pressure, which is just the flip side of vacuum.
          Manifold pressure can be either Positive or Negative.

          While the cylinders are pulling air in, and with throttle plates marginally open, manifold pressure will be on the Negative side.

          With a turbo charged engine, we may see both Negative and Positive manifold pressure..... with the Positive being referred to as "boost".

          Usually it's primary purpose is that it can be used as a measure of engine loading.
          A heavily loaded Marine engine is undergoing near zero manifold pressure.

          If you know the typical idling vacuum and you detect a change or needle bounce you can detect all kinds of things from a vacuum leak to a misfire.
          Yes, and typically with a temporarily connected vacuum gauge, not a permanently connected vacuum gauge that would be at the helm.

          You can use the guage and a speedo to determine your optimally efficient point of cruise...
          As I said earlier, once we begin advancing the throttle, the engine will be under load.
          Manifold pressure at this time will be near zero.
          With a naturally aspirated engine, widely opened throttle plate position (against the constant engine demands) does not allow for us to see much manifold pressure.

          Now, that said, we may (key word "may") see an increase in manifold pressure once the hull is up on step and then that tad bit more.
          In other words, when we get the hull on step and a tad bit more, hull friction is further reduced, therefor removing some of the load in which case we may see a very slight increase in manifold pressure.

          All of this is very much Un-Like a car or truck engine where loads are reduced once rolling down the highway.


          In my opinion, a helm located vacuum gauge, for use on a naturally aspirated marine gasser, is not going to give us much useful info.
          If installing one gives you that feel-good-feeling, then by all means install one.

          Rick E. Gresham, Oregon
          2850 Bounty Sedan Flybridge model
          Twin 280 HP 5.7's w/ Closed Cooling
          Volvo Penta DuoProp Drives
          Kohler 4 CZ Gen Set

          Comment


            #7
            Simiar in some ways to boost gages on diesel twins - I have found vac gages on gas twins to be helpful.
            Northport NY

            Comment


              #8
              With my fuel injected setup, I display manifold pressure, which is just the flip side of vacuum.
              "Manifold pressure can be either Positive or Negative."

              It depends on whether you define the pressure in the manifold in guage or absolute. Fuel injections MAP sensors measure in absolute; IE: 0-100 KPa for naturally aspirated, 0-? for boost (IE: 14.6 psi = 200KPA) etc. As one who has tuned multiple turbo setups, I can assure you that this is the way turbo guys speak about manifold pressure.

              While the cylinders are pulling air in, and with throttle plates marginally open, manifold pressure will be on the Negative side.
              With a turbo charged engine, we may see both Negative and Positive manifold pressure..... with the Positive being referred to as "boost".

              As per above, the only way this would be true is if your are refencing to atmosphere, which no one does.

              Usually it's primary purpose is that it can be used as a measure of engine loading.
              A heavily loaded Marine engine is undergoing near zero manifold pressure.

              I see what you are getting at, but you have said it wrong, and also it's not true. In absolute terms, the pressure is never 0 (Absolute vacuum-that's a good ring seal lol). Even at idle there is typically 30-40 KPA present in the manifold. I think you meant that there is no manifold vacuum when the engine is loaded. This is not true of course, because the only time we achieve zero vaccuum (Or close to it) is when the throttle is wide open. There are many points of cruise where the manifold pressure is at 60-80 KPA, a very measurable difference from 100KPA (WOT). In other words, the throttle is NOT an on/off switch, as either a vacuum guage or MAP sensor signal will confirm. If you run around at WOT throttle all the time then your point is perfectly valid, but I don't know anyone that does this.

              If you know the typical idling vacuum and you detect a change or needle bounce you can detect all kinds of things from a vacuum leak to a misfire.
              Yes, and typically with a temporarily connected vacuum gauge, not a permanently connected vacuum gauge that would be at the helm.

              The difference would be??? I can see that the length of the hose MAY cause a dampening effect on high speed pressure transients, but even then I suspect some would get through.

              You can use the guage and a speedo to determine your optimally efficient point of cruise...
              As I said earlier, once we begin advancing the throttle, the engine will be under load.
              Manifold pressure at this time will be near zero.
              With a naturally aspirated engine, widely opened throttle plate position (against the constant engine demands) does not allow for us to see much manifold pressure.

              As per above, simply wrong.

              Now, that said, we may (key word "may") see an increase in manifold pressure once the hull is up on step and then that tad bit more.
              In other words, when we get the hull on step and a tad bit more, hull friction is further reduced, therefor removing some of the load in which case we may see a very slight increase in manifold pressure.

              All of this is very much Un-Like a car or truck engine where loads are reduced once rolling down the highway.

              Sorry, that's pure BS. Load is load, regardless of what the engine is in. The engine does not know, or care.


              In my opinion, a helm located vacuum gauge, for use on a naturally aspirated marine gasser, is not going to give us much useful info.
              If installing one gives you that feel-good-feeling, then by all means install one.

              Like James Brown I feel good level. LOL!


              If you like this type of stuff, you should really do some reading on tuning-It's really quite cool to learn more about how to properly tune engines, engine dynamics etc.


              Chay

              Comment


                #9
                I disagree that load is load when we are talking a street vs marine application. Rolling resistance is much less that planing through water resistance. This is obvious in comparing fuel consumption between the two. I agree a vacuum gauge in a marine application can provide useful data but when running at a constant rpm on plane I don’t see it as useful. Point is how useful is the gauge vs concern of that long of a vacuum line potential of getting a leak causing an issue. Just my opinion.
                1997 Maxum 2400 SCR 5.7LX Bravo II

                Mike

                Comment


                  #10
                  If your using it for diagnostics that's one thing. OP had a very vague question that blew up assuming it meant gasoline engine and maximizing efficiency. Their signature says Hinos... LOL

                  Continuing the discussion of gasoline:
                  Picking your perfect trim on plane using a 1.5" panel mount vacuum gauge is damn difficult, but it is noticeable. I used my 3.5" gauge with a hose going through a deck to the helm during commissioning of my new long block a couple years ago and was able to see the inflection point for loading based upon changes in tabs and drive. Although more significant was the change in RPM on my tach and exhaust tone

                  Now with the time and expense of installing a vacuum gauge... not worth it in my opinion, install a fuel flow meter instead and listen to your engine exhaust. HP = fuel burn, an average normally aspirated automotive engine will burn about 24 gallons/hr to make 300 hp. Vacuum at idle is about 20-26", so your resolution on fuel flow is greater for high throttle application.
                  Purchasing 1997 3388, in progress.
                  2002 Bayliner 2455 w/ 5.7 MCM BIII

                  Comment


                    #11
                    I disagree that load is load when we are talking a street vs marine application. Rolling resistance is much less that planing through water resistance. This is obvious in comparing fuel consumption between the two. I agree a vacuum gauge in a marine application can provide useful data but when running at a constant rpm on plane I don’t see it as useful. Point is how useful is the gauge vs concern of that long of a vacuum line potential of getting a leak causing an issue. Just my opinion.

                    You have to think not about what you typically do with a vehicle, but what could be done with it.

                    For example, towing my old 20' boat up the hill from Creston to Osoyoos (Or however you spell it), tryst me it was near wide open for an hour. So in that case, I exceeded what I would typically run my marine engines at.

                    When I pull my 2850 up the hill from Port Alberni the old Cummins is working pretty hard, and does for a while.

                    Load is load...

                    Yeah, more typically a marine engine is loaded at a higher rate for longer but this doesn't affect engine management very much. You can expect a little more in-cylinder heat, so a slightly lower spark advanace is required to reduce the liklelihood of knock, we try to keep the coolant temp a bit lower. That sort of thing.

                    Anyway, getting back to the vacuum guage deal, it also matters how much of your installed hp is being used at cruise, and how wide a varierty of cruise speeds you can travel as to whether it has more or less range of utility.

                    For example, a boat with lots of power as compared with it's weight may be able to cruise between 18 and 35 knots, let's say. In this case there will be a larger range of vacuum or if you prefer manifold pressure that the boat can cruise at, so larger deflections in the vacuum guage.

                    If you have an 'just' adequately powered or underpowered boat, then the range of cruise is smaller, and therefore you'll notice less range in the vacuum guage at varying cruises.




                    Chay

                    Comment


                      #12
                      Ok.... it sounds like a bit of clarity is in order.

                      In post #1, Freede asked about the use of a vacuum gauge. He has twin Hino diesels.
                      In post #2, Smitty made the comment; "On gasoline engines - yes."
                      My response in post #3 pertained to Smitty's comment.
                      In post #4, Chay called BS.
                      In post #6, I added a bit of humor and went on to further explain regarding a naturally aspirated Marine engine and whether or not a vacuum gauge would be useful.
                      In post #9, I believe that Mike understands what I've explained.


                      Originally posted by pugetpowered View Post
                      If your using it for diagnostics that's one thing. OP had a very vague question that blew up assuming it meant gasoline engine and maximizing efficiency. Their signature says Hinos... LOL
                      Correct!
                      In my post #3, I was responding to Smitty.


                      Now with the time and expense of installing a vacuum gauge... not worth it in my opinion,
                      install a fuel flow meter instead and listen to your engine exhaust.
                      Bingo!
                      .

                      Originally posted by Chay
                      Part #1
                      With my fuel injected setup, I display manifold pressure, which is just the flip side of vacuum.
                      "Manifold pressure can be either Positive or Negative."
                      I stand strong on my above statement.

                      It depends on whether you define the pressure in the manifold in guage or absolute. Fuel injections MAP sensors measure in absolute; IE: 0-100 KPa for naturally aspirated, 0-? for boost (IE: 14.6 psi = 200KPA) etc. As one who has tuned multiple turbo setups, I can assure you that this is the way turbo guys speak about manifold pressure.
                      Non Relevant.... Filibuster.

                      While the cylinders are pulling air in, and with throttle plates marginally open, manifold pressure will be on the Negative side.
                      With a turbo charged engine, we may see both Negative and Positive manifold pressure..... with the Positive being referred to as "boost".

                      As per above, the only way this would be true is if your are refencing to atmosphere, which no one does.
                      Non Relevant.... Filibuster.

                      Usually it's primary purpose is that it can be used as a measure of engine loading.
                      A heavily loaded Marine engine is undergoing near zero manifold pressure.

                      I see what you are getting at, but you have said it wrong, and also it's not true.
                      Go ahead.... I'm all ears!

                      In absolute terms, the pressure is never 0 (Absolute vacuum-that's a good ring seal lol). Even at idle there is typically 30-40 KPA present in the manifold. I think you meant that there is no manifold vacuum when the engine is loaded. This is not true of course, because the only time we achieve zero vaccuum (Or close to it) is when the throttle is wide open. There are many points of cruise where the manifold pressure is at 60-80 KPA, a very measurable difference from 100KPA (WOT). In other words, the throttle is NOT an on/off switch, as either a vacuum guage or MAP sensor signal will confirm.
                      Again, and all due respect Chay, that is Non Relevant to our conversation.

                      If you run around at WOT throttle all the time then your point is perfectly valid, but I don't know anyone that does this.
                      Nor do I.


                      As I said earlier, once we begin advancing the throttle, the engine will be under load.
                      Manifold pressure at this time will be near zero.
                      With a naturally aspirated engine, widely opened throttle plate position (against the constant engine demands) does not allow for us to see much manifold pressure.

                      As per above, simply wrong.
                      Again, I'm all ears!

                      Now, that said, we may (key word "may") see an increase in manifold pressure once the hull is up on step and then that tad bit more.
                      In other words, when we get the hull on step and a tad bit more, hull friction is further reduced, therefor removing some of the load in which case we may see a very slight increase in manifold pressure.

                      All of this is very much Un-Like a car or truck engine where loads are reduced once rolling down the highway.

                      Sorry, that's pure BS. Load is load, regardless of what the engine is in. The engine does not know, or care.
                      Chay, perhaps you should factor in not only the load, but also the the throttle plate position and the load duration.


                      Part #2
                      I disagree that load is load when we are talking a street vs marine application.
                      Yes, the loads, and perhaps more importantly the load duration, are considerably different.

                      Rolling resistance is much less that planing through water resistance. This is obvious in comparing fuel consumption between the two.
                      Yes again.

                      I agree a vacuum gauge in a marine application can provide useful data but when running at a constant rpm on plane I don’t see it as useful.
                      And that is because the open throttle plate position (on a naturally aspirated engine that is keeping a hull on step) will prevent us from seeing any significant manifold pressure.
                      (I have explained this above)

                      Bottom line;

                      if you are posting in favor of the use of a vacuum gauge, please show supporting data.
                      if you are posting only for the purpose of arguing or debating, keep it civil and friendly.
                      if you're after that Feel-Good-Feeling, go ahead and install a vacuum gauge.


                      One last thing.
                      If you are using the quote feature to quote and to respond within the quote, it helps to change your font color.
                      Rick E. Gresham, Oregon
                      2850 Bounty Sedan Flybridge model
                      Twin 280 HP 5.7's w/ Closed Cooling
                      Volvo Penta DuoProp Drives
                      Kohler 4 CZ Gen Set

                      Comment


                        #13
                        Every constant-speed propeller equipped aircraft has a manifold pressure (vacuum) gauge, either normally aspirated or turbo charged. Just like marine engines these engines are heavily loaded, for long periods. Few automotive engines can be used in aircraft because they can't sustain these power settings.
                        Big difference is the prop. In an aircraft the prop can either be fixed pitch, like a boat, or adjustable. The fixed pitch prop rpm is a throttle function, with 2800 rpm as a normal limit, and there is no vacuum (manifold pressure) gauge. The adjustable prop sets the rpm, with the throttle setting manifold pressure (on a gauge). At max open throttle mp reads high, the less power the lower the mp. Off course, it all depends on how you calibrate a scale. Take-off is almost always full power (with a time limit), and at a certain altitude mp and rpm are reduced to a climb setting, and in cruise even further reduced. Turbo charged engines can have a mp up to 48", and a descend requires planning to slowly reduce mp to avoid cracking engine blocks or turbo's. Engine life can be from 1400 to 2500 depending on size, turbo charged or not.

                        Comment


                          #14
                          The above is a good point re: variable load with constant rpm. The benefit there is obvious.


                          In a diesel engine, of course there is no throttle plate, and therefore no vacuum (Or very slight vacuum) in the manifold. If turbo, typically a pressure guage would be installed, and would correctly be called a boost guage. After knowing how the engine typically performs a boost guage will give you instant feedback if something is wrong with the intake/fueling/turbo and is a very valuable tool.

                          However, I have identified and fixed a flakey blockage in the intake tract of a diesel using the output of a MAP sensor. It read normal pre boost of 100ish kpa, then a decent vaccuum of about 60kPA , so even then there are times when a vacuum guage is of use on a diesel.

                          Even with a diesel engine, especially the newer common rail computer controlled versions, we use a MAP sensor, which reads from 0-300ish KPA, depending on design, IE: 3 atmospheres absoute. No positive and negative vaccuum....lol.

                          2850 Bounty...you seem to be a stickler on terminology, so as to speak a common language about issues. That's the reason I'm trying to help you, but whatever. Say it however you want I guess.

                          But, if you are actually saying that as you advance the throttle you vacuum goes instantly to 0, then you must not have done this in real life-Nothing could be further from the truth. The ONLY time this happens is when a tuner kid thinks moving from a 25mm throttle body to a 50 mm throttle body will help him go faster lol.

                          As far as load duration causing issues internal heating issues, this is true of course, but the real question is how long do the internal parts and cooling system take to respond to a load change? If the answer is 10 minutes, then any load beyond 10 minutes will cause the same temperatures to exist in the engine, regardless of what it is installed in. The engineers have to consider worst case scenario-They sure as heck aren't limiting spark advance and fueling and A/F ratio based on an unloaded highway cruise.

                          So, given an engine type, an extended period of load, load is load. Where we differ is that you don't think this load profile can exist on the road. i don't know what you use your truck for, but I assure you I use it like this all the time.

                          Anyway, whatever.


                          Chay

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