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Thread: 8v, 16v, Can someone explain?

  
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    8v, 16v, Can someone explain?

    Basically... I'm far from a mechanic, and i know that 16v is better and quicker.. Aparently smoother too?

    But lets just say for example a 1.8 8v and a 1.8 16v astra (i'm not getting either but people know about these engines so might help for explaining)

    Basically.. What is the valves, like what do they do? And when there is more why is that faster? or more BHP or whatever it is that makes it better?

    I'm sure a fiat coupe has 24v aswell... Is that really needed?!


    Sorry, random thread, just been on my mind a bit why its better..

    Cheers, Jang
    ~Not long now people~

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    SXi Stu
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    valves are moved up and down with the movement of the camshaft, they control when fuel is let into the cylinder so more valves mean more fuel getting into the cylinder to be combusted, hence more power. Think thats right anyway lol

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    Quote Originally Posted by Jang
    Basically... I'm far from a mechanic, and i know that 16v is better and quicker.. Aparently smoother too?

    Some drag cars have only 2 valves, one in and one out. They aren't too bothered about mpg figures though

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    Quote Originally Posted by Millen99
    Some drag cars have only 2 valves, one in and one out. They aren't too bothered about mpg figures though
    So with that theory, 8v is better then 16v performance wise, but less on MPG..

    Now i'm confused more then a nun in a pornshoot.


    Jang.
    ~Not long now people~

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    have a read of this for general background gen on how engines work

    http://auto.howstuffworks.com/engine.htm

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    Quote Originally Posted by Jang
    So with that theory, 8v is better then 16v performance wise, but less on MPG..

    Now i'm confused more then a nun in a pornshoot.


    Jang.

    That all depends on the size of the valves.

    A 16v will probably be more economical as the extra valves help deliver the correct amount of fuel at the correct time. Inlet valve lets in the fuel/air mixture.....combustion....exhaust valve(s) let out exhaust.

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    It's more to to with the total area of the apertures of the valves then the number - the valves in an 8v engine are larger than those in the 16v. But the total area of the two valves in a 16vis bigger than the single valve in an 8v.

    Simple geometry

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    16V will allow more air in for a given engine speed.

    the 8V runs out of torque as the revs go up, as the air can only get thought the valve opening so fast.

    the 16V can get more air in at higher revs.

    Generally, 8Vs make their torque at low revs, 16V at higher revs.

    There are exceptions though.

    the X22XE (16V) Frontera/Omega engine makes 136BHP, but 150 lbft at 2600rpm, which is more like an 8V torque curve.
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    I was gonna suggest that How Stuff Works article, but geoff beat me to it!

    Its a good article though, helped me understand engines a whole lot more!
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    8 valves will run out of puff top end but give far better torque low down as a general rule but there are axceptions. Quite a lot of the time it's simply a case of moving your power around the rev range. 8v will give better low end power than a 16v, and 16v will give better performance top end.

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