OHV vs. OHC

Discussion in 'OT Driven' started by Possum Stomper, Aug 25, 2003.

  1. Possum Stomper

    Possum Stomper The Great Bird of the Galaxy

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    i really don't have a preference so long as they work, but i am wondering why all of the ricer and euro eliteists insist on OHC

    have a look at the LS1 (to a lesser degree the LT1?) and alot of the engines they make in Australia and you see big power matched with decent economy and drivability

    so why all the fuss? :confused:
     
  2. flynfrog

    flynfrog Cool isnt Cheap

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    vetc yo jdm tight
     
  3. Whitey Ford

    Whitey Ford New Member

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    The only Australian designed engine is the Ford 4L inline 6 cylinder found in the most popular car in the Ford Australia lineup, the Ford Falcon. It's had OHC since 1990 and DOHC since the current model. Every other engine is either imported from other countries or designed elsewhere.

    The flexibility that is afforded from a DOHC inline engine is fantastic. You can greatly angle the valves and it allows for more efficiently designed heads. I'm a 302/5L pushrod ford guy at heart, but the advantages of DOHC or even SOHC are immense. Pushrods do a job, they do it well. However, better technology exists and is being implemented.

    Example, the current Falcon 4.0L inline 6 puts out the same power as the 5.0L V8 from a Falcon 4 years ago, because the 6 now has DOHC. It's all there on paper, imports arn't the only cars using DOHC you know.
     
  4. CussCuss

    CussCuss New Member

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    DOHC is a better design than SOHC or OHV designs, simple, but theres more factors such as cost and space and other things.

    To put it simply, the reason smaller engines usually have DOHC is to produce more power with the available displacement, bigger engines dont really need to do this(also a DOHC v8 has very big heads)
     
  5. matt_c

    matt_c Guest

    i really don't care, so long as the car goes fast :big grin:
     
  6. coronet

    coronet Do Andriods Dream of Electric Sheep?

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    SOHC :: Lighter in Weight, best for racing (see Corvette's Le Mans racing results)

    DOHC :: Heavier, but better for us un-racers.
     
  7. matrix243

    matrix243 My body, is ready.

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    Physics...More direct driving valve train, less chance of failure, smoother operating, higher rpm range. I don't really know much about the modern ohv designs but pushrod and rocker failure is emminent with valve floating or piston-to-valve contact.
     
  8. Possum Stomper

    Possum Stomper The Great Bird of the Galaxy

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  9. Possum Stomper

    Possum Stomper The Great Bird of the Galaxy

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    well the S7 and C5R have OHV engines, as does the Viper, they don't seem to be having trouble with parts OR power (not that i am complaining)

    you have to at least respect that fact without getting all pissy about the engine config :mad:
     
  10. matrix243

    matrix243 My body, is ready.

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    There using the 351 windsor block in the S7. Bigger supply of parts available, and weight might be a consideration for racing.
     
  11. Possum Stomper

    Possum Stomper The Great Bird of the Galaxy

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    i am aware ofthe blocks origin, but it is still a street legal motor (barely)

    anyone else care to chime in or is this topic dead to you all :hs:
    maybe if i put itin the import section
     
  12. MAD PUNK inDC

    MAD PUNK inDC Sic Semper Tyrannis

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    You're actualy alot more likely to bang the valves and damage something on an OHC engine, than on an OHV one. Also pushrods tend to bend and give way before serious valve, or piston damage is done. OHV engines also tend to be more compact and lighter, and are alot easier to work on.
     
  13. Possum Stomper

    Possum Stomper The Great Bird of the Galaxy

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    mad punk check your mail :wavey:
     
  14. CussCuss

    CussCuss New Member

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    no, there is nothing wrong with pushrods, they are infact newer than ohc designs.
    People who bitch about how the engine is technically superior are useless.
    It doesnt matter how you get the power and if anyone says otherwise they need to open their mind a little.
     
  15. matrix243

    matrix243 My body, is ready.

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    I personally prefer the OHV design because I've had experience with them. True the pushrods will let go before anything. I've had 2 fail, and only damaged part of the intake manifold. Also OHC gives you the option of multi-valves, not just a single intake/exhaust.
     
    Last edited: Sep 4, 2003
  16. matrix243

    matrix243 My body, is ready.

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    Care to elaborate?
     
  17. CussCuss

    CussCuss New Member

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    ohc was invented before ohv, when someone calls the ohv dinosaur technology its technically wrong.
     
  18. matrix243

    matrix243 My body, is ready.

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    Don't think I've ever heard that before. I can see it being developed for smaller 4 cyl motors. Not sure about the other V-8's, but the flathead had pushrods.
     
  19. CussCuss

    CussCuss New Member

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    i doesnt really have anything to do with v8's
     
  20. 67olds442

    67olds442 uhhhh

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    I"m pretty sure its 100% true, i don't have the time to look for any proof but I've heard it many times.

    OHV is newer then OHC
     
  21. MAD PUNK inDC

    MAD PUNK inDC Sic Semper Tyrannis

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    Ford, Olds, and Caddy all had OHC engines, before OHV, so did Mercedes Benz.
    Also just because it's pushrod, doesn't meen you cannot have a multivalve, head, or even one with variable timing. Look for something called "Hot Rocker" and Dominion's 32v heads for small block Chevys. These are just a couple of examples.
     
  22. idontgiveashit

    idontgiveashit I eat rice

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    i saw a 350 chev in a hotrod i think, with porsche something or other heads mated to it somehow, dual overheadcam.
     
  23. bigsteve7

    bigsteve7 OT Supporter

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    I think the main reason euro and eastern import guys like OHC designs is because they typically rev higher. This is do to a number of reasons which I wont get into, but when dealing with smaller displacement engines like the Japanese and European cars typically have, revs are essential for making horespower.

    It can also be argued that its easier and more reliable to engineer a variable valve timing system into a OHC design than a OHV. Same with mutli-vavle designs.
     
  24. Possum Stomper

    Possum Stomper The Great Bird of the Galaxy

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    they should try out a few OHV's then :big grin:
     
  25. matrix243

    matrix243 My body, is ready.

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    Here's some advantages disadvantages of the designs I found.

    "It's all about inertia and breathing here. The key to high specific output (meaning HP per liter, or cu. in.) is breathing and low pumping losses. In the '60's and 70's, to get more HP out of a given displacement a manufacturer would install bigger valves. HP comes from cramming more air and fuel into the cylinder, so a bigger "door" (valve) can let in a bigger air/fuel mixture per stroke . The problem with a bigger valve is that a bigger valve weighs more than a smaller one (assuming the same metallurgy), and this means to control the extra weight as it's flung open is the spring that closes the valve has to be stiffer. A stiffer valve spring (multiplied by the number of valves), means more energy is spent overcoming the valve pressure, thus partially offsetting the gains of a bigger valve. Another disadvantage of a big valve is that at lower RPM's, the intake charge has a lower velocity and low RPM torque and driveability. suffer. Enter a mulitivalve design. Two 30mm valves give more breathing area than a single 60mm one, and each valve weighs less than a 60mm one, as well. I can hear you saying "but TWO 30mm valves weigh more than a single 60mm one!". True, but for each cam lobe, there is less mass to overcome, and the smaller valves don't have to open as far nor do the valve springs have to have as much spring rate. A 4-valve design almost gives you something for nothing, as at lower RPM's the intake velocity is good for each port (they're small ports) so you get good low RPM torque and driveability., while at high RPM's there's sufficient flow (there's two ports) to make good HP."

    "Another advantage of a DOHC design is it makes it easier to add variable valve timing. Not all DOHC designs implement this, as it adds cost, but with variable valve timing, the engine can dynamically adjust the intake and exhaust timing to give an even better spread of low RPM and high RPM power. Honda/Acura, BMW, and Nissan/Infiniti are some of the manufacturers that have variable valve timing on some of their DOHC engines.

    The drawback of DOHC? Cost (more parts, more money), packaging (the cylinder head is bigger due to all the cams and valves up there), and maintenance (you have to adjust twice as many valves)."
     

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