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engine configuration + differences

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by BiX, Dec 19, 2005.

  1. Whats the difference between all the different engine configurations? eg does one need to be rev'd heaps for power while other have low down torque but no power? whats easier to ride?

    parallel twin
    inline triple
    inline 4
    flat twin
    v4 (edit)


  2. v4 could be added to that list as well
  3. simple rules for those who are not willingn to do research

    1. for the same engine speed and capacity, the engine with the most cylinder capacity will produce the most torque.

    2. power is merely torque produced at engine speed.

    3. for engines of same capacity (and flywheel inertia), the engine with the most cylinders will spin the fastest.

    4. for engines of equal displacement, more cylinders is usually more vibration free. (the triples can be a bug bear here and fours with balancers shit all over everything).

    5. all other things being equal, more cylinders = more expensive, more cylinder heads = more expensive.

    You should be more interested in how they feel to ride, how they sound, how expensive are they, is a high centre of mass important (ie flat engines in big traillies) and so on.

    If you haven't bought a bike yet, just go and test ride them all.
  4. Yikes BiX, you don't want much :D
    Alright, my 2c
    V-Twin, lots of torque and great note with a good set of pipes
    Parallel twin, torquey, can be vibration-prone if not ballanced internally by balance shafts.
    Triple, torquey but also good power up the rev range
    AFIK there are no triples on the market that aren't in-line
    In-line four is the biggest category, characteristics depends on what sort of bike they're in
    Flat twin, BMW, loads of torque
  5. I'm told they also make bikes with just one cylinder. Fancy that!
  6. But only masochists buy them :LOL:
  7. I thought it was more down to stroke length. A longer stroke seems to allow for better torque at lower revs, because of the length of the expansion stroke, and the amount of rotational torque that can be applied. The length of the stroke is determine by the crank-shaft. Much more torque applied to a crankshit pivot point that has a larger radius than a small radius, for the exact same reasons why you can crank screws into wood better with a fat screw-driver handle than a thin screw-driver handle.

    A short-stroke engine has less rotational torque.

    Problem with a longer stroke is that it increases piston speed per revolution, increasing the mechanical stresses when the piston has to change direction. With a short-stroke, the piston speeds are lower, the stresses are there-fore lower, and you can correspondingly raise the peak rev limit. Power = torque x rpm. So it's all about balancing the reduction in torque with a shorter stroke, with increasing the rpm's to compensate to provide more overall power.

    Given the same capacity, having fewer cylinders generally means larger bores and/or longer strokes than having more cylinders, unless we have stupendously a over-square stroke on the low-cylinder engine, typically creating combustion inefficiencies.

    The exact reasons for any one type of configuration over another all depends on what the target goals are, the available space, and whether or not the engine can be balanced without shaking itself apart.
  8. One thing not mentioned so far is fuel economy. Large displacement twins, in flat or mild 'V' configurations, are usually more fuel efficient than multi's for distance work. The reason is that once the mass of those two big pistons get's going, their kinetic energy means that less energy is required to keep them going. In town of course this is not so, as getting that reciprocating weight up to speed in stop-start riding cancels the advantage. The limited complexity of most well designed twins also makes them more inherently reliable. The final factor is CofG, a flat twin like a BMW has a very low CofG, and for rough or off road riding it makes a heavier bike more managable than a vertical multi. For these reasons, (and I am happy to be corrected), I am not aware of any bike more popular with 'adventure' riders or 'round the worlders', than a big twin. The closest I think is the Triumph Tiger triple, but it does have a higher CofG.

    EDIT - Nothing in this post should be taken as implying in any way that a Harley Davidson is actually a motorcyle.
  9. inci, the inertia argument only works for straight line kinetics. Reciprocating masses expend energy from the flywheel on the high points of the sinusoidal motion curve.

    The real reason for the fuel efficiency is more likely to be different tuning for different roles. The real reason a 1200cc bmw twin produces less torque and power than a 996cc ducati twin is....
  10. Happy to except that, but practical experience over 40 years tells me that If you shut the throttle in a too-tall gear on a big twin it will keep rolling a lot farther than a 4cyl multi. Likewise, in a shorter gear the engine braking is much greater. I am not an engineer, but both of these seem to indicate purely mechanical differences.
  11. flywheel sizes, overall gearing, losses on shaft drives compared to chains, valve timing differences, higher losses in the big, flat twin balancers (1150's anyway), overall bike/rider mass...

    Yes there are mechanical differences, however they do not point directly to fuel economy as you stated, nor is fuel economy related to reciprocating mass. You are correct about the fuel economy facts, however i don't believe in your reasoning.

    edit: compression ratios on big twins also tend to be lower than the fours, because their high octane fuel supply is not as readily guaranteed.

  12. As stated, I am happy to be corrected on the specific mechanical reasons. The fact remains, in the context of the OP's question, that large displacement twins make more suitable distance mounts than multis.
  13. back to your regularly scheduled programming....
  14. So many other configurations have been tried in production bikes:
    Square 4 (2 Parallel twins)
    Flat 6
    Parallel 6
    Radial (Don't think anyone will try that again though)
  15. Another point worthy of consideration is traction. V-twins in particular, because of their staggered power impulses, create a "rest" phase in the engine cycle, which effectively allows the rear tyre to recover a bit of grip between power impulses. Whereas four (and a triple) will tend to get the rear spinning and keep it spinning (because the impulses are closer together), the twin gives the tyre a mini-break between hits. This is the great advantage that Ducati exploited (especially in in WSB ) to allow their bikes to get on the gas earlier and power out of corners faster than the competition, even though they had less top end horsepower.
    The same characteristic eats chains and sprockets, though.
    On the subject of vibration, it seems that for some reason (engineers??) 90 degree v-twins and v-fours produce mainly horizontal (forward-backward) type vibration, which most people seem to find pleasing rather than the more annoying vertical or lateral vibration.
  16. There are many a difference even in the same genre of engine, The R1200C Unlike BMW's other Boxers got increased bore and stroke, decreased exhaust and intake valves and an altered intake tract to provide for more low-end torque so as to behave more cruiser like.
    This coupled with fuel-injection made the throttle response abrupt, to say the least, so twitchy was the outcome, this model cruiser was not a big seller.
  17. Some other very odd configurations have been tried. The 'double knocker' 'T' comes to mind, essentially a beam engine with no rotating crank. It was quite spectacularly unsuccessful. Also the 'H' configuration, which is essentially a square 4, with two opposed cylinders. Again not a winner, at least not in bikes. (In WW2 they built an 'H'16 for aircraft that was very powerful indeed.)
  18. not to mention the drysdale V8
  19. ... and BRM built a 1.5 litre H-16 for Formula One racing too,

    http://www.yorkwa.com.au/Motor.Museum/1967BRM.htm etc, etc

    It actually won a race in a Lotus frame, but you would have thought after the trouble BRM had with the V-16 back in the 50s that they'd have run a mile from ever fiddling with 16 cylinders again......

    inci, that museum in that link is in WA, are you familiar with it?
  20. I think there were some H16 configuration aircraft too.

    The v16 was quite a well thought of engine in cars.

    That is how Cadillac got it's name. They were straight 8's and v-16's before Chevy bought them and wrecked the whole deal.

    Must notably, however, was the Duesenberg. It had a v-16 and was considered the finest luxury car every made. hence the phrase "she's (or it's) a real Duesy!"