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Understanding basic engine specs

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by kate, May 3, 2016.

  1. I am interested to know a bit more about engine specs from a purely scientific perspective. Specifically:
    • Air-cooled and water/liquid cooled engines
    • Single cylinder, twin parallel and twin v engines (or other types of multi-cylinders)
    • Bore and stroke
    In the experience of riders here on the forum, how do these influence the handling and/or performance of different bikes?

    I am asking mainly out of curiosity, as I see these things referenced on the forum and would like to understand more about what different engine parameters actually mean in application. I already have an idea of the sort of bike that I would like to buy as my first, so this question isn’t related to my choice of bike, more for the satisfaction of my analytical newbie brain :)

  2. Air cooled engines are simpler and was the method of cooling for years. Certain cylinder configurations don't work well in air cooled structures because the cylinders at the rear get less air and so run hotter. Liquid cooled engines overcome this limitation and allow you to get more horsepower out of the same size engine. There is extra complexity of a radiator, water pump, cooling fans etc but more horsepower is the goal.

    Re Engine types, a good Visordown article: Every type of four-stroke bike engine ever made

    And another on Bore and Stroke, you generally refer to the ratio between the two: Understanding Bore and Stroke
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  3. #3 Dark Angel, May 3, 2016
    Last edited: May 3, 2016
    This is a HUGE discussion, not just in terms of defining the various terms but in explaining how they interact with each other and other concepts not mentioned but equally important.

    I'll get the ball rolling with your first post. Cooling.
    Air cooling means the engine gets rid of excess heat by heating the air in contact with the engine. Water cooling means there are passages inside the engine filled with a water based coolant that carries the heat to a radiator for removal. Water cooling has advantages over air cooling such as absorbing engine noise and more stable temperature control which has follow on performance implications. Air cooling can result in a lighter, simpler engine, which also has performance implications.
    Add to that various hybrid solutions such as air/oil cooling and BMW water head/air barrel cooling and things can get even more complicated, with every engineering solution having various advantages and disadvantages. Everything is a compromise.
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  4. #4 BitSar, May 3, 2016
    Last edited: May 3, 2016
    But of course we all know 'air' cooled is a generous term as oil cooling is the 'real' heat transfer medium. The oil still requiring a radiator to dissipate heat.

    That said, the counter argument is that all engines are 'air' cooled as the water in the journals of a liquid system get rid of heat via an air flow radiator.

    Go figure.

    In terms of cylinder configuration, get anything other than an inline 4 for good times, great character and a ride which requires mechnical sympathy.

    My preference is as such.
    V2 > i1 > i2 > i3 > V4 > i4
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  5. Thanks cjvfrcjvfr for these excellent links. The articles were exactly the type of explanation I was looking for and connected so many dots for me. Thanks for introducing me to the Visordown site. Heaps of great info over there!
  6. #6 Harb, May 3, 2016
    Last edited: May 3, 2016
    I like your curiosity (y) Hopefully some of what comes next makes some sense.

    Taking a step back, all of this is related to 4-stroke petrol motors. For every two revolutions of the crankshaft you get one intake (down), compression (up), power (down) and exhaust (up) stroke per cylinder. The greater the RPM, the more power strokes there are - this is why power is directly proportional to RPM. The configuration of the motor (single, V2, I2, I4, etc...) determines the configuration of crankshaft for best balance and when each cylinder is at which stroke across these two rotations, which is 720 degrees. As such you can have numerous types of V2s, I2s, and so on, each with their own advantages and disadvantages. Manufacturers often have multiple ways to do things with modern engineering like adding weights to counter imbalanced motor harmonics. This is a pretty good video on that.

    CJs link above details bore and stroke well, also giving you the formula to relate torque and power. Larger capacity cylinders, with a long stroke will naturally have more torque at low RPM but be too unbalanced to reach higher RPMs all else being equal. Likewise, they will have more engine braking on a closed throttle and be more prone to locking the rear on poor downshifts.

    Power delivery through the chain/shaft/belt and onto the wheel also change the characteristics, and this is entirely due to configuration and firing order. Singles put heaps of power instantaneously to the rear wheel, then provide nothing for the remaining 630 degrees of crankshaft rotation. Even firing I2s (360deg crankshaft) will power with less delay, and typical I4s will provide consistently smooth power. But a 180 degree or 270 degree I2 will be more like a single. See wikipedia for a graphical depiction of when the power stroke appears across the 720 degree cycle in singles and twins. You might be able to see how this relates to the acceleration feel and wear and tear on chains and sprockets from that wikipedia article. This also makes or beaks the distinctive sound of bikes like Harleys 45deg V twins, Ducatis 90deg V twins and your typical 1000cc supersport I4 (try and compare this sound to the newer R1s which have a different, crossplane I4 crankshaft).
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  7. Watercooled engines tend to have tighter tolerances and tuned to a higher degree which enables greater power output at the expense of added complexity.
    Most high performance engines and sports bikes are water cooled, this also has the benefit of not blowing up if you can't filter and always keep moving.
    A middle ground is bikes like the GS500's and older GSX's which have a radiator sized oil cooler infront of them to still be simple but also generate a respectable amount of power.

    More cylinders the more complexity, more fuel, more maintenance and generally smoother power delivery. All things the same
    Single cylinder = 1 piston going up and down, very basic and easy to maintain
    Found on your CB125E and CBR250R

    Parallel twin = 2 pistons, Goes up and down at the same time as the single one (or completely opposite each other), twice as many valves, carbs and sparkplugs. For the same size 'cc' engine the cylinder is half the size as the single and the piston may not need to go down so far (stroke) which can make it higher reving.
    Generally a very predictable simple engine and reliable design, common on the Ninja's.

    V-Twin: 2 pistons and cylinders in a V shape. Twice as many heads, cams and cam chain tensionors.
    Tend to sound sweet, be nice and torquey and have plenty of power down low.
    Are more expensive to manufacture and maintain.
    Honda make some good units: VTR250

    Inline 4:Similar to the parallel twin but with 4 cylinders. Can generate allot of power, power band tends to be very high, can sound nice. Fair bit of maintenance (4 of everything).
    This is your common goto engine for most sports bikes.

    V4: Same deal as the inline 4 being similar to the parallel twin but with the V-twin.
    Looks like the V-twin engine but with another bank of cylinders behind it.
    My experience on a VFR800 has been very smooth , lots of torque, fun to ride and very very linear power in all gears and it sounding orgasmic :p
    Expensive to buy and maintain? Most likely
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  8. +1 for V2!!!!!
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  9. The short response is: it depends.
    Some smaller engines don't use oil for cooling at all. As they get larger there is more waste heat so using the oil for cooling becomes more useful. Early GSXR Suzukis were mostly air cooled but added oil jets under the pistons and an oil cooler. My R1150 has extra oil passages in the heads specifically for cooling while the barrels are air cooled.

    I notice everyone is avoiding 2 strokes.
    For the OP: this term means that the engine produces power once every two piston strokes. Everything a 4 stroke engine does in four strokes is done in two with some clever design and valving. The sound and power delivery are different, both more dependant on exhaust system design than a 4 stroke. They're lighter, simpler, and can make more power than a 4 stroke BUT they tend to be less civil to ride at high power output and the need for oil in the fuel mix (details of which are a big topic on it's own) make them smelly and dirty.
    These are good examples of a disadvantage of air cooled engines. There were a number of three cylinder two stroke bikes years ago from several manufacturers. The middle cylinder tender to get less air flow and was more prone to seizing from over heating. The Suzuki "waterbottle" two stroke triple didn't do this as the water cooling gave more stable and even cooling across all three cylinders.
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  10. Here lay dragons.

    The problem with this sort of discussion is there is as much marketing, opinion and bullshit as there is fact.

    Just reading through the few posts above there was already a number of point on which my Engineering brain disagrees. Unfortunatly some things are so embedded in motoring culture, that trying to tell people they are incorrect is just impossible.

    And it really is a huge topic. Hundreds of engineers (probaly thousands actually) are employed around the world looking specifically at vehicle engines and it's been that way for a hundred years

    Maybe tell us the motorcycles you are considering and we can give our opinion of the relative engine characteristics of those bikes.
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  11. Air vs water cooling:

    I've had both, and still do. Some pros and cons.

    Air cooled engines can be lighter - no radiator, water pump, hoses, extra layers of metal in the engine to form a "jacket" for the engine. HOWEVER, they are noisier - there is less metal between the moving parts and the outside of the engines. You can hear the mechanicals. They run hotter when it is hot. They don't go so long between rebuilds. There is greater wear associated with the large fluctuations in temperature over the operating cycle of an air cooled motorcycle engine. They tend to be harder on oil. Air cooled engines benefit more from short oil change intervals. I like to use a lighter grade of oil in the colder months, heavier for the Summer heat.

    Water cooled engines have shorter "warm up" times. When it is cold, particularly, the warm up time might be half that of an air cooled engine. A short period of idling when you zip up, put on the helmet and glove up is generally enough before moving off, and the normal amount of power is available sooner. There is the prospect of having an engine going as long as a car engine before it needs a rebuild, particularly in larger bikes which don't have to work at all to ride at legal speeds. You can use the same oil Winter and Summer. Air cooled bikes are "overcooled" at temperatures around Zero, or lower; they might seem cold a long way down the road. When it is really hot, you can mostly relieve yourself of concerns of overheating with liquid cooling. So long as your engine keeps its coolant inside, it will be at an acceptable operating temperature. An air cooled engine that has been out on the road at 40 degrees plus, then has to endure a dozen stops at lights when travelling through towns will get hot. On a liquid cooled bike the cooling fan will just run more. Whereas the air cooled engine will get noisy and you will find yourself thinking about how thin the oil might be getting and how much wear you are producing and new noises, real or imagined, on a really hot day. They'll just keep going and wear out faster. There will be a bit of an imperative to get and keep an air cooled bike moving to keep some air flow through the cooling fins when it is hot. However, liquid cooling adds another system which adds complexity to regular maintenance and a vulnerability. - Hole the radiator, lose your coolant due to a leak and you are done. Damaging a radiator in a prang adds to the cost of repairs.

    Which is better? Its horses for courses. I sometimes miss the familiar "ring" of the fins on some of the air cooled bikes I've owned (yeah, it's a nostalgia thing) I'm liking the engine longevity of liquid cooling, don't like the weight or the prospect of coolant loss stopping me outright, but recognise that liquid cooled engines can go harder for longer when worked to extremes in real heat. Liquid cooling on competition trail bikes is recognition of this.

    There's my line of BS for the day.
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