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    V6 or I6?? What's the difference?

    Kung Fu Sifu

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    V6 or I6?? What's the difference?

    Post  Kung Fu Sifu on Mon May 11, 2009 12:18 am

    This may be a crazy question for some of you but besides the fact that one motor is in a straight line and the other is positioned in a V shape, what is the difference between them. I see so many RB26DETT / 2JZ-GTE motors pushing out over 1000hp but only see very few V6's come not even close. Does the I6 motors get more air flow since the intake manifold goes straight to all 6 cylinders or what. I don't know, someone pplleeaasssee enlighten me. I've done plenty of searching but never found anything that explained why! Come one guys help me understand this!
    Supa Ninja

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    Re: V6 or I6?? What's the difference?

    Post  Supa Ninja on Mon May 11, 2009 2:47 am

    also has to do with the exhaust manifold/turbo manifold, I know they love being turbo charged. Ya I'm in for the answer too.
    Huggy Bear

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    Re: V6 or I6?? What's the difference?

    Post  Huggy Bear on Thu May 28, 2009 2:16 pm

    So far the only thing I know is since the way the pistons are angled vary's, the force from them "shakes" the engine in a different way. That's why boxer, flat, "pancake," or however you want to call them engines help cancel out those forces (according to the car makers who feature them, like Subaru and Porsche).

    Vibration is a key difference of various engine configurations. Inlines are not ideally balanced, and suffer from "second order" vibration--vibration frequency that's double the engine RPM. Most inlines are fitted with a balance shaft, basically a shaft that spins in the same direction as the crankshaft and is weighted to counteract vibrations.

    Inline 6s, however, are dynamically balanced and free of 1st and 2nd order vibrations. All other inlines (within reason, I have no idea what an inline 12 would be like) are not balanced, and are either rough-running or need crankshaft counterweights and balance shafts.

    "Boxer" engines, or horizontally opposed engines like those in Subaru and Porsche are also balanced and free of first and second order vibration. Interestingly, the boxer configuration is the only one that is balanced no matter how many cylinders are used (even numbers, of course). That's why boxer, flat, "pancake," or however you want to call them engines help cancel out those forces (according to the car makers who feature them).

    V engines are not dynamically balanced and suffer from varying degrees of vibration. Most 90 degree V engines are generally smooth, though the crankshaft arrangement (crossplane or flatplane) can effect smoothness. 60 degrees is the ideal bank angle for V engines, though no V is particularly smooth by nature, and many employ a balance shaft. Volkswagen "VR6" engines are extremely "narrow angle" V6 engines (about 10-15 degrees), though because they use a single valve head for both banks, they can really be considered Staggered inline 6 engines. These engines are inherently rough-running, but balance shafts smooth things out, and like other V6 engines, the result is generally smooth operation from the driver's perspective.

    I can't see any good reasons why any one arrangement will produce more or less power than the other. Given the freedom to design the engine without space/cost restraints, engineers can make intake plenums and exhaust headers to suit any arrangement, and the rest of the meaningful engineering takes place in the combustion chambers, which don't particularly care if they're arranged in a V or in line.

    However, there are quirks to some arrangements. A cross-lane V, for example, is one in which the Crankshaft has 4 Crankpins with each pair of opposing pistons sharing a single crankpin. This is nice and smooth without balance shafts, but requires a heavy counterweighted crankshaft, and is thus best for torquey, low-revving engines. A Flatplane crank, in which opposing pistons are connected to the crankshaft by pins 180 degrees from each other, is lighter and favors quick, fast revs, but needs balance shafts to keep it smooth. Notice that's Ferrari's enormously powerful (for its size) 4.3 Liter V8 is light weight revs past 8000 RPM. That's a flatcrank engine.

    Inline engines with 6 or more cylinders have traditionally been limited by the tortional rigidity of their longish crankshafts. As we all know Torque and HP go hand in hand. The more torque you use in the engine is the less you put to the ground. Which means more power will be used for your unsprung weight. Modern materials and production techniques have largely solved this "problem," but the fact remains that anything more than 6 inline cylinders will need to be engineered with this in mind, which may limit overall performance.

    There are always exceptions to these tendencies. Honda's 4cylinder engines are glassy smooth and free-revving. The V6 that appeared in the Acrua NSX was ferociously high revving. The previous Generation BMW M3, with its long straight 6, was also an 8000RPM+ screamer. So higher revs equal longer throttle opening, which equals more possible air. But as said before it’s all on the producer. Ideally, an I6 would net more air to the cylinders individually, but a V6 would net more air total as it employs a plenum type manifold. Is it possible to grand horse power a V6? Yes it is. But with a low revving engine you may have to do extra work to get there, but it will totally crush you with torque. But it can be done.
    Case in point, While the F1 is a V12, it’s NA and produces 630 HP and 480 LBS of torque STOCK! It is also built on the same principles for V engines mentioned above.

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    Re: V6 or I6?? What's the difference?

    Post  jesse on Thu May 28, 2009 10:59 pm

    good write up huggy and nick.

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