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  • #16
    Originally posted by A.K. Boomer View Post
    They do not have to be concerned as much with stoich anymore, ...
    OOOOOOOOOOOOOOOOOOOOkkkkkkkkkkkkkkkkkkkk.

    -Doozer
    DZER

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    • #17
      Originally posted by Doozer View Post
      OOOOOOOOOOOOOOOOOOOOkkkkkkkkkkkkkkkkkkkk.

      -Doozer
      If there's something you do not understand about that statement then just say so,

      You think diesels are concerned with Stoichiometric ratio's ? all's they care about is if they have enough air to burn whatever their going to be injecting into the chamber -- and overkill on the air ratio is not an issue,,, actually and technically diesels are always "running lean" with way more air than fuel (unless your into "rolling coal") - they can do this due to not having to compress a pre-mix of air and fuel - yeah, kinda like what's going on with todays direct injection gas,,, you no longer have to have a perfect ratio of air and fuel... you can have and do have many times more air than what is needed like at idle - no throttle plate, full charge of air yet tiny little spritz of fuel just enough to keep it running...

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      • #18
        My understanding of common PCV valves is that they are basically vacuum regulators, included to keep a small vacuum on the crankcase.

        Even the old road draft tubes were arranged to create a small vacuum, at least at road speed.

        On many vehicles using constant depression carburettors (SU, Stromberg, etc.), there was often a port on the carb that provided a relatively constant small vacuum. This port was connected to the crankcase to maintain negative pressure.

        I always assumed that most modern vehicles used negative crankcase pressure.

        Ed
        For just a little more, you can do it yourself!

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        • #19
          Before egr valves most IC engines had either a breather which consisted of a small compartment full of wire mesh, linked by a tube to the intake manifold, the idea was that the oil condensed on the mesh and was sucked back into the sump on the up stroke, and any blowby gasses went into the inlet to be burnt in the cylinders. A high mileage engine would breathe heavily into this system, and all the residue would end up in the carb and manifolds. Some also had a valve which would allow pressure to escape as the piston came down, and shut when it was going up. Usually a very simple spring and disk valve.
          Man who say it cannot be done should not disturb man doing it! https://www.youtube.com/user/philhermetic/videos?

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          • #20
            Originally posted by A.K. Boomer View Post
            If there's something you do not understand about that statement then just say so,

            You think diesels are concerned with Stoichiometric ratio's ? all's they care about is if they have enough air to burn whatever their going to be injecting into the chamber -- and overkill on the air ratio is not an issue,,, actually and technically diesels are always "running lean" with way more air than fuel (unless your into "rolling coal") - they can do this due to not having to compress a pre-mix of air and fuel - yeah, kinda like what's going on with todays direct injection gas,,, you no longer have to have a perfect ratio of air and fuel... you can have and do have many times more air than what is needed like at idle - no throttle plate, full charge of air yet tiny little spritz of fuel just enough to keep it running...
            You said gasser first, not diesel; which are you actually talking about? Stoich is very important in a gasoline engine, regardless of the type of intake system. Diesel is a completely different thing. Your post said, referring to your earlier post about "gassers", that "They do not have to be concerned as much with stoich anymore", which is completely incorrect.

            Strokersix - one example of an engine not using a throttle plate is Nissan's VQ37 motor used in the 350Z and G37 cars starting in about 2008. That motor does have dual throttle bodies, but doesn't use them for air control during normal engine operation, instead it controls the intake by variable valve lift and timing. Obviously they still control the fuel mixture to be near stoichiometric, like pretty much any other gasoline engine.
            Last edited by Yondering; 06-14-2019, 01:30 PM.

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            • #21
              Originally posted by brian Rupnow View Post
              I read yesterday about a small single cylinder i.c. engine model that had a "regulator" that kept a slight negative crankcase pressure in the engine while it was running. This was a 4 cycle vertical engine with a "wet" crankcase. The negative pressure kept any oil from migrating out around the crankshaft bushings. I hadn't heard about that before and I think it is a great idea. The engine in question was the Silver Angel by Bob Shores. A visual inspection of this engine running on YouTube shows no connection from the carburetor to the crankcase. The only "oddity" I see is that the engine seems to have double oil filler caps side by side. Does anyone have more info about this?---Brian
              Brian, as some others pointed out, negative crankcase pressure is used in some high performance engine applications. It doesn't require a vacuum pump on a single cylinder engine, just a check valve of some sort. I use one on my dirt bike; it's a one-way check valve in the breather hose, that hose is just plumbed to the air box so it doesn't really produce any significant vacuum on it's own. The cylinder pulses in the crankcase produce the vacuum, and it helps ring seal. Several automotive applications use similar check valves, I could probably dig up some part numbers if you want.

              The vacuum produced in the crankcase is noticeable when trying to drain the oil; barely any oil comes out until the filler cap is removed to break the seal, even with the engine shut off for several minutes. If you're building an engine with exposed seals that may tend to pass more air, the previously voiced concerns about dirt intrusion might be an issue depending on operating environment, but on a sealed crankcase the system works pretty well.

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              • #22
                Originally posted by Yondering View Post
                You said gasser first, not diesel; .
                Wrong, I stated "direct injection gasser" which in fact is getting to the point of technically being called a diesel, just one that runs on gas instead...

                also as stated - some are not even using spark plugs anymore...

                Again - here's all you need to know, even the ones using plugs do not have a throttle plate, so it's a full charge of air even at idle,,, now how would you get an engine like this to idle without a T-plate IF you were trying to use a stoichiometric ratio of fuel and air? you could not - it would take off in an instant - so - when you know theory of operation like I do - it means you control it by fuel amount - just like a diesel and in fact just like a diesel stoichiometric is a non-issue,,, you can do whatever you please with ratio as long as there's enough air (oxygen) to burn the amount of fuel injected, so 18 to 1 is just fine - along with 100 to 1 as long as the 100 is the air part.
                Last edited by A.K. Boomer; 06-14-2019, 02:37 PM.

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                • #23
                  Sorry boomer, you're off base on this one. Gasoline internal combustion is not like diesel combustion, you're missing some important details. Diesel can be made to run really rich to produce more power, gasoline doesn't work that way. Air intake is still regulated, just not with throttles.

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                  • #24
                    Sorry - and were not talking about rich here were talking lean - and air intake is not regulated anymore, it's wide open just like a diesel, all the variable cam timing in the world will not change this fact that the valves are opening and are not restricted, you need to study up on how these engines are controlling their RPM's and power and then get back to me on it. thanks

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                    • #25
                      Originally posted by A.K. Boomer View Post
                      Sorry - and were not talking about rich here were talking lean - and air intake is not regulated anymore, it's wide open just like a diesel, all the variable cam timing in the world will not change this fact that the valves are opening and are not restricted, you need to study up on how these engines are controlling their RPM's and power and then get back to me on it. thanks
                      Yeah, the new engines are very funky compared to the old. I was working on my 2016 lexus that has two injectors per cylinder. That threw me for a loop. One "low" pressure and one high. JR
                      My old yahoo group. Bridgeport Mill Group

                      https://groups.yahoo.com/neo/groups/...port_mill/info

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                      • #26
                        I have my Upshur Twins set up with check valves on the crankcase vents. The valves are derived from Jerry Howell's design for his V-twin, but his design combined the crankcase vent with the fuel level control. The Upshur Twins are boxers with the pistons in phase, so the crankcase volume change from TDC to BDC is quite significant. The vents seem to do a good job of keeping the oil in, because in cases when the reeds don't seat correctly due to a valve misadjustment, I get a lot of oil weep.

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                        • #27
                          Brain is asking about the negative pressure in a rather specific application. Namely the use of a one way valve to maintain negative pressure in a model engine crankcase as an aid to avoiding oil leaks on an engine that has no seals on the crankshaft. The replies seem to be all over the map trying to match this application to larger multicylinder engines. I'm not sure that the comparisons apply. And in some examples they clearly don't apply.

                          While the PCV valve used on pretty well all automotive engines these days will likely see some slight amount of vacuum in the crankcase under some conditions I doubt it'll be anything like the suction draw that would be present in the single cylinder engine which is the topic of the thread question. A single cylinder will produce a huge volume change with every stroke due to the volume sweep of the single piston.

                          Brian, in this situation with only a one way valve pumping the crankcase down to a lower pressure I think I'd worry a little about oil to the main bearings. Now if the other cap has a small bleed hole or light spring loaded ball valve such that the vacuum is limited then all would be well and good. Oil viscosity and surface tension in oil is a strong factor that will ensure good lubrication. And a slight vacuum will stop the oil from gushing out the outer ends of the bearings.

                          And you DID say "regulator". And in such a case a simple ball valve and adjustable spring along with the one way reed would combine to regulate the case pressure (drop). And I can certainly see it eliminating the need for seals if set to just the right value.

                          It would be like a kid with a runny nose sniffing back the snot just before it drips out with each cycle of the piston..... .
                          Chilliwack BC, Canada

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                          • #28
                            Originally posted by A.K. Boomer View Post
                            Sorry - and were not talking about rich here were talking lean -....
                            Stoichiometric is in the middle of rich and lean.

                            -D
                            DZER

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                            • #29
                              Was gonna say, isn't this similar to just about every crankcase breather system I've ever seen? Older chevys had the PCV from the valve cover to the base of the carb (where the vacuum is highest), Briggs and Stratton lawnmower systems had a similar setup with a flap valve next to the muffler, breathing into the carb. In both cases there is a one-way valve and the pressure "pulsates" slightly between positive and negative during normal (cruise) operation. Having a slight vacuum in the crankcase helps the ring seal.

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                              • #30
                                While everyone was yakking about diesels, the plan fairy flew up, perched on my computer, and shat out the drawing of the crankcase pressure regulator on the Silver Angel. It is a simple 3/32" diameter ball setting in a tapered seat with a very light spring holding it in place. Pressure inside the crankcase lifts the ball off it's seat and escapes. Suction in the engine pulls the ball deeper into it's tapered seat and doesn't let any air in. This gives a negative pressure in the crankcase. The engine has splash lubrication. This lubricates the main bearings, the big end of the rod, and the wrist pin. I would have to think the atmosphere inside an engine with splash lubrication must be full of a very oil heavy mist.
                                Brian Rupnow
                                Design engineer
                                Barrie, Ontario, Canada

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