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Bore stroke comparisons...

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by hazard121, Jul 17, 2005.

  1. Im currently comparing the R1 and GSXR1000 just for research and im comparing the stock bore x stroke and was wondering what the differences mean??

    YAMAHA R1 - 77.0 x 53.6
    SUZUKI GSXR1000 - 73.4 mm × 59 mm

    any infomation would be good thanks..


     
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  2. Not sure what your after, but bore and stroke are the measurements of the bore (diameter) and the distance the piston moves from top dead centre to bottom dead centre in the cylinder.

    so (using your figures) ...
    the R1 has a cylinder diameter of 77 mm, and a stroke of 53.6 mm
    GSXR1000 has a cylinder diameter of 73.4 mm, and a stroke of 59 mm

    These figures can be used to give you the "swept volume" or the volume that the piston will "sweep" in its travels up and down the cylinder, add that to the volume of the combustion chamber, times by the number of cylinders, and you get the capacity of the engine.

    In GENERAL terms, a bigger bore than stroke (called "oversquare") is a used in high revving motors that strive to gain power.

    Comparing bore and stroke of two different engines by itself it's pretty meaningless, too many other factors involved. It is interesting to compare the Bore and Stroke of two versions of the same model, just too see how it is used by the engineers to improve some aspect of engine performance. Adding a bigger throw crank (increasing stroke) for example can give torque benefits, at the expense of power due in part to a drop in max revs.

    Hope that helps.
    JJ
     
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  3. The yamaha ahs a bore of 77mm and a stroke of 53.6mm. That means the piston moves up and down 53.6mm each time the crank spins. The diameter of the cylinder is 77mm.

    Hence the GSXR has a stroke of 59mm and bore of 73.4mm. Engines made to these diametres, where the bore is bigger than the stroke, are known as "oversquare" engines. Most car engines have a longer stroke than bore.

    The difference in bore and stroke changes the power dynamics. The R1 is known for having a brutal power delivery, which the dimentions would no doubt have something to do with. The GSXR has big HP but is better off the bottom and thru the nidrange, once again a condition of the engine dimentions.
     
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  4. Yep, Iffra is right. You can't just compare the bore and stroke as there are too many other factors.

    An "oversqaure" engine revs harder and generally produces more power. As a by-product, it also allows bigger valves which also impacts upon power output.

    An "undersquare" engine, where the bore is longer than the stroke, produces less power but more torque. Most older engines were undersquare but in car terms the change took place with the 105E Anglia in the early 1960's where the bore and stroke ratio changed dramatically. From memory the bore was around 98mm and the stroke aound 48mm.

    Must be said that motorcycles used the oversquare design earlier than it was adopted by cars in the wider sense.

    O'square=high revs=highpower
    u'square=low revs=high torque
     
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  5. More like,

    oversquare=>torque peaks at higher revs
    undersquare=>torque peaks at lower revs.

    Provided the two engines are of equal capacity, the maximum torque values they produce will be within a few percent of each other.

    Googling around just now, I stumbled across,

    http://www.nightrider.com/cyclerama/cycleramaport.htm

    The report on a dyno shootout among some variously tuned 1340cc Evolution Harleys. At 88x104mm bore and stroke, that's about as long-stroke a motorcycle engine as you can find these days.

    Note torque peaks of the order of 90ft-lbs.

    Compare that to a Hayabusa; 1300cc, 81.0x63.0mm bore and stroke.

    One place to find a dyno chart for one is here,
    http://www.sportrider.com/bikes/dynos

    Note torque peak of 98.4ft-lbs.

    An oversquare engine, due to being able to rev higher, will generate a higher peak power calue than an undersquare engine, but an undersquare engine_will_not,_in and of itself, be able to generate a higher peak torque value than the oversquare engine.
     
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  6. Hypothetically speeking, say if i was to buy one of the above bikes just on the borexstoke which would be a better bike to buy?
     
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  7. Depends on what you want your bike to do. The engine with the longer stroke will probably have a tad more torque down low, thus making it a bit easier to ride. That may also mean that you might be able to ride it quicker, if you're not that adept at handling high revving engines and doing lots of gear changes.

    When it comes down to it, I doubt very much that your or I or most of the others here on Netrider would be able to tell the difference, nor would we be able to make use of those differences.

    I'd probably go for the GSX-R because it looks nicer......

    :)
     
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  8. What he said. Buying a bike based on such a limited and highly esoteric standard would probably leave you disappointed. You need to look at the factors of a bike that are most important to you and buy on that basis. That includes many more things than just power; comfort, handling, appearance, gearbox, adjustability, etc, etc.
     
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  9. Interestingly some cars are going back to more square proportions.

    Basically the 4-valve configuration allows better efficency, so it's easier to fill a long cylinder.

    Also modern quality control and manufacturing techniques mean that the higher piston speed created by long strongs is less critical to engine wear.

    Suzuki probably went to the longer stroke to reduce the engine width. This is something they have done with previous models.

    To answere your hypothetical question, if you had two bikes identical in every respect except for the boreXstroke, I'd personally take the longer stroke. I ride on the street and I am realistic about which part of the rev range I use.
     
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  10. Many years ago, the old man said that the maximum piston speed that conventional engines (bike or car) could tolerate was 35 mph (about 58 km/h).

    Recently, I recalled what he said and tested the theory based on my CBR1000F's redline and cyl. dimensions. It wasn't that far off. I think that at 11,000 rpm redline piston speed was about 36 mph or thereabouts.

    And this is from a theory that dated back to the 50s or 60s.

    It'd be interesting to see the engine specs of a 990 GP bike or even that of an F1 where 18,000 rpm engine speeds are common. Of course, they can't do it for that long, either....

    I just did some quick calcs in Excel. The engine with the shorter stroke (the R1?) at 11,000 rpm has a piston speed of 43 mph and the longer stroke engine is running at 48 mph.

    As I don't own either of these bikes, I don't know what their redlines are set to. But going by these figures, for the same piston speed the GSXR would have a 1,000 rpm lower redline.
     
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  11. do you know the rod lengths for these motors or are you just doing average speeds?
     
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  12. Conrod length is irrelevant. It can be a few inches or 10 inches. The stroke is still the same. That's dependent on crankshaft diameter or the throw.

    As for how I worked it out, I simply multiplied the stroke by 2 to get the total distance travelled in one RPM. I then multiplied that figure by the RPM, eg, 11,000 rpm. That gives you distance travelled in one minute at that rpm. Then I multiplied that figure by 60 to give distance travelled in one hour. It's many millimetres, so I divided it by 1,000,000 to get kilometres. I then converted it to mph by multiplying it by 0.62137.
     
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  13. Not quite right mjt. Rod length determines rate of acceleration to maximum piston speed & decceleration back to zero. I think you will find that this is the determining factor in max piston speed (rate of acceleration) although not to such a degree as the stroke. Drag racers play around a bit with rod lengths to give best torque characteristics for their requirements. Changing rod length changes the dwell time at the top of the stroke allowing higher cylinder pressures to be generated & vise versa
     
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  14. A week ago, you were telling us about getting your L's and asking about if you should buy a naked bike, and now you're asking about brand-new litre bikes.

    Why do I get the impression you're trying to waste people's time?
     
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  15. I'm trying to picture this in my mind, but am having difficulties with it. Might be a nightshift thing (I missed a glaringly obvious joke in another thread a few minutes ago).

    Perhaps I should have quoted "mean" piston speed, given that it starts and stops 4 times during one revolution.

    Thing is, the piston travels x distance in one revolution. Multiply that by the number of revs in a given period of time and you get a speed measurement. I dunno how much effect conrod length will have on that, or indeed, in the engine's upper rev limit, other than extra mass that has to be thrown about...
     
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  16. they are both SO fast you probably wont buy one because of the bore and stroke.

    as far as I know, big bore/short stroke make power at higher revs, which is
    what I've heard about the R1 - higher revs, more manic power delivery,
    whereas the gixxer apparently has a wider power band.

    (never ridden either though)
     
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  17. Yeah, the ratio of stroke to rod length is pretty important. It determines maximum piston speed and, as noted, acceleration. So longer stroke engines are not only taller by the amount of extra stroke, but also by the amount of extra rod needed.

    You can of course just stroke an engine and shorten the rod length to leave your deck height the same, but engine ware would increase significantly. It also goes to vibration.

    So my bet is the Suzuki would be a taller, narrower engine then the Yamaha. The rev comparison is hard unless you know the rod length
     
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