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Combo Engine

  1. Aug 21, 2005 #1
    Hi friends,
    Can we construct an engine that can shift its engine capacity i.e. CC. Means if we are looking for power , we can go for option with higher capacity & when we demand for better milage we can go for engine with lower capacity.Is there any such engine available?
    Any help is welcome.
  2. jcsd
  3. Aug 21, 2005 #2
    The new chyrstler Hemi C is an 8 cylinder, but it turns off 4 of the cylinders on the highway to get better gas milage. All you would have to do is cut off the fuel injection into the cylinders you dont want to use, and leave the exhaust valve port open so it doesnt have any compression. Although that would require quite a big of modifications, and would'nt be very nice
  4. Aug 21, 2005 #3


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    In addition to some of the new Chrysler Hemi (the high-performance models don't get it), Mercedes Benz has had it on their V12 for a while now, GM has it on their 5.3L and 6.0L V8 engines (not the Corvette one) and notably had the most famous implementation in the early eighties Cadillac that didn't work very well.

    Honda is suppossed to offer the DOD (Displacement on Demand) technology on their Accord V6 and in theory other manufacturers are doing the same or considering it now that the technology is reliable and becoming a selling point.

    Something like 10-15% increase in fuel economy because of the reduced pumping losses.
  5. Aug 21, 2005 #4
    DOD via multiple motors

    You could also use several engines and turn them off separately according to how much power is needed. This might be easiest to implement in a serial ICE/electric hybrid.

    I was thinking this might be a good idea for long-haul trucks. The need very little power on the interstates. They also have a hard time in snow, so there might be electric motors on each wheel and an ICE by each wheel so that the truck could have 18-wheel drive (or 10-wheel drive for a truck with super-singles).

    And for braking, just hook the motors up to resistance sinks.
  6. Aug 22, 2005 #5


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    Working at Honda, I am somewhat familiar in their system. If you are familiar with the VTEC system, it is based on the same principles. At the desired engine load, an oil pressure switch opens allowing oil pressure into the system. The rocker arms then "lock" forcing the outer rocker arms to follow the inner cam lobe which typically doesn't control anything.

    Doing this, when that particular engine condition happens, the cams force the valves to open when they would be normally close so compression doesn't occur. Then they simply cut fuel.

    As far as the other system, I imagine their systems are similar, but I can't give exact details.
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