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  • Active Fuel management Cylinder Deactivation Technology

    Can anyone give a better explanation of how this works or is more fuel efficient other than four cylinders are not firing, other than what is described here "four of the eight cylinders is switched off and a solenoid system collapses the valve lifters to reduce the pumping losses and improve fuel efficiency."

    OK, I get that, you shut the valves off basically........ So either your compressing the trapped air as the piston goes up or creating a vacuum as it moved down. Either way there is a drag.
    Your turning half a dead engine.
    Trucks have jake brakes, opens the exhaust valves and the enging breathes in and out of the exhaust. That creates quite a bit of drag as it slows the truck down.

    How does the drag out weigh the fuel that is being saved?

    To me, it more stuff to go wrong and working on today's motors are not fun.

    https://gmauthority.com/blog/gm/gene...on-technology/

    JL...........

  • #2
    I think the first line of the link you left says it all.

    The philosophy behind Active Fuel Management is to increase fuel economy while not reducing performance or resorting to force-inducted smaller engines.
    It's for those fence riders that want their cake and eat it while hoping not to gain weight.
    For those hoping to get traditional V8 power while still getting somewhat decent mileage this approach has it's followers without the perceived angst some have by using a turbocharged 4 cyl.
    Will it ever get the fuel mileage a true 4 cylinder engine will get? No
    However it is a low tech solution to those that cannot let go of their beloved V8 engines.

    The frictional loses can never be erased so it can never be as efficient as a smaller displacement engine. It is a low cost solution though for those not expecting huge gains in mileage while still getting the power they need or want. It's a no-brainer decision since it is so easy to implement and does have it's benefits.

    Air in the cylinder or a vacuum will however have a negligible effect since any change in pressure will be returned on the opposite stroke. This is why diesel engines require something like a Jake brake. Even with a compression ratio of say 18:1,and no restriction of the intake air flow, most of the energy used to compress the air is returned back to the crank on the subsequent down stroke.
    Home, down in the valley behind the Red Angus
    Bad Decisions Make Good Stories​

    Location: British Columbia

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    • #3
      Not all 4 cyl are better mileage than larger engines. On the old S10, I had a 4.....Rated at 29 mpg, never even got close. Others that had the optional 6 routinely got better mileage than I did, by 2 to 4 MPG.

      Near as I can tell, they did not have to floor it very much, while the 4 had insufficient power (as well as a 4:10 rear end) and just ended up being at WOT or at least more throttle more of the time.

      The Ranger has 270 HP, but turbo 2.3l (or so) 4 cyl. It is advertised at 25 MPG. I have a long term average MPG at the moment of about 23.9 mpg, which I think is impressively close to rated considering that we are coming off winter, when mpg went down severely. It's been over 24 prior to winter.

      That looks like a good system. Good mileage, and still has the power when needed. The S 10 had neither, it could not get out of its own way, empty, and I needed a clear mile or more ahead to pass on a 2 lane road.... didn't do much passing.
      CNC machines only go through the motions

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      • #4
        My friend had a car with what I think they called the 8-6-4 system. He hated it.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          Originally posted by darryl View Post
          My friend had a car with what I think they called the 8-6-4 system. He hated it.
          Those Caddy engines felt terrible when they ran in 6 cylinder mode. Vibrated like crazy. The electronic controls were primitive and the lucky owners that had limited exposure to 6 cyl. mode due to their operating conditions loved them. We disabled lots of them over the years.
          Joe

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          • #6
            I'm doing extensive work on our Honda odyssey. Their design was horrible and I am disabling it. There are a few items that allow it to be bypassed and they are relatively cheap.

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            • #7
              If the cylinders deactivate themselves automatically
              then that is PASSIVE fuel management.

              A Jacobs brake pumps air.
              Cylinder deactivation does not pump anything.
              That is the difference.

              -Doozer
              DZER

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              • #8
                My truck has it 2010 sierra 5.3. All I think it's ever done is cause it to burn oil TBH. It's a problem with the variable displacement engines. It's not noticeable when driving at all, and I'm not sure how much it really affects MPG, maybe a point or two. Buddy of mine lost an engine when one of those fancy lifters collapsed in his. The dealer said it happens a lot on these trucks, so it's not a risk free trade off. I'm closing in on 300k with mine, and feel like I'm playing blackjack with it every month now....

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                • #9
                  Originally posted by JoeLee View Post
                  ...
                  OK, I get that, you shut the valves off basically........ So either your compressing the trapped air as the piston goes up or creating a vacuum as it moved down. ......
                  On the upstroke, air is compressed, as you say. THEN, on the downstroke, that compressed air drives the piston. Basically storing energy then recovering it. Probably a lot of wasted energy. Would be better to just leave both valves open all the time (if it wasn't an interference engine).

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                  • #10
                    Iv always hated that concept, no matter how you cut it your still going to have piston ring drag/ reciprocating losses and also minor pumping losses even with valves wide open or totally shut down and trying to rely on spring effect --- in the latter air is still being heated and that heat dissipates to the piston and cylinder walls, heat that is created is added friction and parasitic drag,,, Im really surprised they can get any positive results at all...

                    My little 1 liter three cylinder would fall on it's face if it attempted such an archaic measure... if it dropped one cylinder id be dead in the water lol

                    instead it does what the old WW2 pilots used to do to conserve fuel and make it back to base even when "technically" not having enough fuel to do so,,, It goes "lean of peak" and it only does it at opportune moments when cruising and not needing much power to do so - so the engine is not even making enough power to "hurt itself"

                    it goes into a 26.5 to 1 Air-Fuel ratio,,,, and it does so without having a meltdown because it is so lean and using so little that it surpasses pre-ignition and detonation concerns,,, this is all done for me by sensors and computer control, it's also something that I do not believe you will find on anything newer because it does increase NoX emissions and my car somehow just squeaked in and was given a pass,,, now direct injection gas has changed the rule book so my car does not have quite the advantage of what it did at the time it was built...

                    imagine trying to do this with carbureted engines, this is how our great past pilots got many a war bird back home, just enough power to keep them afloat, low low demand and then lean to the point of stumbling and then enrichen just a frogs hair and watch your pyrometers like a hawk along with air speed....

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                    • #11
                      Originally posted by Willy View Post
                      I think the first line of the link you left says it all.



                      It's for those fence riders that want their cake and eat it while hoping not to gain weight.
                      For those hoping to get traditional V8 power while still getting somewhat decent mileage this approach has it's followers without the perceived angst some have by using a turbocharged 4 cyl.
                      Will it ever get the fuel mileage a true 4 cylinder engine will get? No
                      However it is a low tech solution to those that cannot let go of their beloved V8 engines.

                      The frictional loses can never be erased so it can never be as efficient as a smaller displacement engine. It is a low cost solution though for those not expecting huge gains in mileage while still getting the power they need or want. It's a no-brainer decision since it is so easy to implement and does have it's benefits.

                      Air in the cylinder or a vacuum will however have a negligible effect since any change in pressure will be returned on the opposite stroke. This is why diesel engines require something like a Jake brake. Even with a compression ratio of say 18:1,and no restriction of the intake air flow, most of the energy used to compress the air is returned back to the crank on the subsequent down stroke.
                      Willy, I couldn't see where it would get true 4 cyl. mileage either. There is drag to take into consideration regardless of how much of it is balanced out by compression on one cylinder and vacuum on an opposite cylinder. Friction is a good way to put it as you did.
                      With electronic / computerized fuel injection I would imagine the fuel is increased to the other 4 firing cylinders to compensate for the drag so the driver doesn't have to keep playing with the gas pedal when the cylinders cut in and out. That makes a seamless transition.
                      I wonder if there are any test specs on exactly how much fuel is saved.

                      JL................

                      Comment


                      • #12
                        Originally posted by Bob Engelhardt View Post

                        On the upstroke, air is compressed, as you say. THEN, on the downstroke, that compressed air drives the piston. Basically storing energy then recovering it. Probably a lot of wasted energy. Would be better to just leave both valves open all the time (if it wasn't an interference engine).
                        I thought about this also, but if the valves were held open when the 4 cyl. shut down then those cylinders would have to be vented some how or somewhere. Where or how would you do that? they would have to be muffled or it could get pretty noisy, also filtered or all kinds of crap could get sucked in. That complicates the whole thing even more.
                        And when they switch back to normal mode I'm sure you would feel it.

                        Lat fall I took a 700 mile round trip with a friend to pick up some machinery I bought. He drove his wife's new Chevy truck. That was the first time I rode in anything with this technology, he wasn't sure how it worked either but when he mentioned it and made me aware of it I could feel when the engine was switching in and out, it was pretty subtle and if he didn't mention it I probably would have just dismisses it as some wavy rolls in the highway.

                        JL..........

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                        • #13
                          Originally posted by A.K. Boomer View Post
                          Iv always hated that concept, no matter how you cut it your still going to have piston ring drag/ reciprocating losses and also minor pumping losses even with valves wide open or totally shut down and trying to rely on spring effect --- in the latter air is still being heated and that heat dissipates to the piston and cylinder walls, heat that is created is added friction and parasitic drag,,, Im really surprised they can get any positive results at all...

                          My little 1 liter three cylinder would fall on it's face if it attempted such an archaic measure... if it dropped one cylinder id be dead in the water lol

                          instead it does what the old WW2 pilots used to do to conserve fuel and make it back to base even when "technically" not having enough fuel to do so,,, It goes "lean of peak" and it only does it at opportune moments when cruising and not needing much power to do so - so the engine is not even making enough power to "hurt itself"

                          it goes into a 26.5 to 1 Air-Fuel ratio,,,, and it does so without having a meltdown because it is so lean and using so little that it surpasses pre-ignition and detonation concerns,,, this is all done for me by sensors and computer control, it's also something that I do not believe you will find on anything newer because it does increase NoX emissions and my car somehow just squeaked in and was given a pass,,, now direct injection gas has changed the rule book so my car does not have quite the advantage of what it did at the time it was built...

                          imagine trying to do this with carbureted engines, this is how our great past pilots got many a war bird back home, just enough power to keep them afloat, low low demand and then lean to the point of stumbling and then enrichen just a frogs hair and watch your pyrometers like a hawk along with air speed....
                          I've noticed that with street bikes and cars, loose a cylinder due to plug fouling or something and you feel it.
                          Any of us that have rebuilt motors and have rotated the crank , even with out the heads being on, no cam or valve spring resistance know how much drag there is turning everything.

                          JL............

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                          • #14
                            Originally posted by JoeLee View Post
                            With electronic / computerized fuel injection I would imagine the fuel is increased to the other 4 firing cylinders to compensate for the drag so the driver doesn't have to keep playing with the gas pedal when the cylinders cut in and out. That makes a seamless transition.


                            JL................
                            If it's an older throttle plate design the driver would still need to compensate as you need air along with that fuel, they could get around that with having a by-pass compensator but here we go with even more complexities...

                            the vehicles with these systems should be crushed and made into something useful like beer bottle openers....

                            Comment


                            • #15
                              I am looking forward to trips like this again --- 73.5 mpgs on a single smaller US gallon

                              iv taken a big hit this winter, with all the cold starts and winter fuel and short trips im at around 55 mpg's

                              the cars average over the course of about 150,000 miles is 59.5 mpg's not too shabby


                              for all the effort put into this thing they also skipped one area --- there's no preheat from the exhaust header to the air intake and Im going to be changing that for next year....



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