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Volumetric Efficiency

Discussion in 'XJ Technical Chat' started by Mechanic1978, Jul 16, 2021.

  1. Mechanic1978

    Mechanic1978 Active Member

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    I planed to write my own article on this however my time and patience is low, for typing long form descriptive articles. So here is a link for a long technical explanation on it, or second link is for a descriptive video. neither article or video is mine, so give your respect to thier original authors.


    In Depth Article:

    https://link.springer.com/chapter/10.1007/978-1-4899-7204-0_10


    Short Form Video:

     
  2. Franz

    Franz Well-Known Member

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    This must be one of the reasons modern vehicles have variable valve timing? Do any motorcycles have dephasers to alter cam timing?
     
  3. Mechanic1978

    Mechanic1978 Active Member

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    yes this is the main factor pushing all engine design since the introduction of the "smog" laws in the early 80"s Im not informed on any current production bikes, but I'm more than certain there in the R&D phase by now...
     
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  4. Polock

    Polock Well-Known Member

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  5. Franz

    Franz Well-Known Member

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    Quite smart it has like a selector drum on the right to move and retract the camshaft onto another sprocket.
     
  6. Mechanic1978

    Mechanic1978 Active Member

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    I replace about 3 to 6 VVT solenoids a day on cars, so this is not something that is completly mechanical, it still relys on an electricaly produced movement to activate any VVT system. the systems are also efficancy based designs, not for optimum power. they can help in power output, but most current systems that have been deployed today us still for the fuel economy, and pollution efficancy.

    edit.. wow my spelling sux!
     
  7. Minimutly

    Minimutly Well-Known Member

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    Well....
    Austin Rover in the uk developed a different system, they called it vvc. Instead of just rephasing cams or using different lobes they had four seperate inlet cams on one shaft, and actually slowed down the cam (relevant to crankshaft) as the inlet valve started opening. At low engine speed they had short duration, as the rpm increased the duration increased, 255 degrees to 285 plus apparently. Gave a good low speed economy, torque and emissions, and screaming 7800 rpm power.
    So effectively 5 cams in one 16v engine. The issues were with noisy epicyclic mechanisms in high mileage, and lack of expertise setting them up. I have a pair in my workshop, one hasenoversise valves, gas flowed head etc.
     
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  8. Mechanic1978

    Mechanic1978 Active Member

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    understandable, but more moving parts means more posability for one to fail. thats why standard VVT is a phasing of the oil flow to adjust the actual cam phaser rotation. thus only added mechanical part is the phaser its self (inner part mounted to the cam and outter phaser), with an external solenoid valve to adjust the already flowing oil. and no more than an average of 20 degree movement in either direction, so a 40 degree max of movement.

    HP gaiss are based on overall increas in rpm... and dont typcalls exceede no more than 20%... in terms of power I take a supercharger, or turbo and get more HP gains,

    in terms of fuel economy and polution vvt is the way to go
     
    Last edited: Jul 16, 2021
  9. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Alfa Romeo's system was entirely mechanical.
     
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  10. Mechanic1978

    Mechanic1978 Active Member

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    it had to have had a type of clutch (varriator) that was deployed based on rpm then, as usually the PCM tells it when to react.

    you have any reference literature to share on that one? @k-moe
     
  11. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    It used a variatior. I don't recall there being any PCM used in the early 80's. The ignition system was similar to the TCI that our bikes use. I didn't keep any of the articles I had about it.
     
  12. Mechanic1978

    Mechanic1978 Active Member

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    I do remember what your talking about. reasearch what a variator is.. its basically what was used back then for that vvt system to work. its similar to a centrifigual clutch operation, but uses rollers wrather than hinged shoes. or a single shoe with a weight and spring.

    here is an early 80's centrifugal VVT variator off the alfa-romeo your refering to. the small springs were known to colapse under prolonged heat, rendering the design ineffective, and often out of time on the valvetrain. luckly zero clearance engines did not exist back then..lol
    nord gear.JPG

    and no this was mechanical, not computer controlled, but there was automotive computer controlled engines back then. but required a "prom" to be swaped out on the board to reprogram or change settings/tolerances.
     
    Last edited: Jul 16, 2021
  13. Minimutly

    Minimutly Well-Known Member

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    Say you. There we are then, must be right
     
  14. Mechanic1978

    Mechanic1978 Active Member

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    so is that a slandering I see there?
     
  15. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    I know what a variator is (I love scooters as much as I love Motorcycles).

    I misread your reply to me. The explanation will be very helpful to those members who do not know what a variator is (which might just be most of us).
     
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  16. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Nope. He's agreeing with us all. :)
     
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  17. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Well, it sounds like a pain in the arse, and complex as all get-out, but it sure is creative and sounds quite impressive.
     
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