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Thread: Difference between Short & Long stroke engines?

  1. #11
    Rusted chicane1879's Avatar
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    ^^Awesome information about the engines.

    There is a thumb rule that an engine is regarded as a short stroke unit only if the stroke is around the 50mm mark.
    ...and this was news to me!!

  2. #12
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    Quote Originally Posted by Joel View Post
    @Payeng - The R15 does not qualify to be regarded as a long stroke motor and the pulsar is not a short stroke motor. The R15 at 57 x 58.7mm is still considered as a square unit.
    The best short stroke engine in India is the Comet 250 and the ninja 250.
    Among the singles, the CBZ is class leading at 63.5 x 49.5mm followed by the RTR @ 52.9mm.
    Ok.. but that the closest that our "desi" bikes come to be termed as short / long stoke.

    The RTR 160 was heavily promoted (in the print media) to have an Overquare (Short stroke) Engine when it was launched in 2007.



    Quote Originally Posted by Joel View Post
    There is a thumb rule that an engine is regarded as a short stroke unit only if the stroke is around the 50mm mark.
    Had no clue about that.. can I get to read more about it somewhere?




    Last edited by payeng; 05-11-2010 at 06:31 PM.
    My Bike Diary: Bike Chronicles of India





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    An excellent information... thank you all...!!!

  4. #14
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    Below are the images of three crankshaft [CBZ(63.5 mm bore), CBR 150(63.5 mm bore), CRF 150R(66 mm bore)] all having an engine with 1.2 bore/stroke ratio and around 150 cc capacity, but conceptualised totally with different applications in mind. The huge difference in the size/weight of the crankshaft in comparison of con-rod and piston, is evident.

    Also, the ZMA with almost the same crankshaft weight as that of CBZ but with lighter piston and 40% more engine capacity and 33% bigger carb, would naturally rev better.

    This bore/stroke categorisation based on below 1, 1-1.2 and more than 1.2 ratio is the primary equation while designing an engine but is subservient to piston speed Ft/second number also. So, two engines with 1.2 ratio but with vastly different piston speed would behave differently.

    Let us full stop here. Newcomers ki jaan loge kya.
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    The Original CBZ

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    @Payeng - The stroke factor applies to full race derived engines.
    The RTR160 is still a short stroke mill considering its got a ratio close to 1.2.

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    Rusted samschenker's Avatar
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    Really nice info here. Thanks to Payeng/Joel/Technician & everyone who is contributing to this thread.

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    Rusted Binoy's Avatar
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    Thanks for the info guys...
    ...Ride Long...Ride Safe...

    When you dance with the devil, you wait for the song to stop...

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    Quote Originally Posted by payeng View Post
    The cylinder size along with the cubic capacity (cc) is also specified as "Bore x Stroke" dimensions.

    Bore: The Diameter of the cylinder block

    Stroke: The Depth of the cylinder block





    Short Stroke Engine (also called as Over Square Engine): The Stroke is "shorter" than the Bore.


    >> Engine Character of a Short Stroke Engine: Engine revs fast due to a relatively shorter stroke, good for bikes where fast build up of Power is essential (eg. track / race bikes)

    >> Eg. of Short Stroke India bikes:

    Apache RTR 160 (62mm x 52.9mm) /180 (62.5mm x 57.8mm),
    Pulsar 150 (58mm x 56.4mm)/180 (63.5mm x 56.4mm)/220 (67mm x 62.4mm)





    Long Stroke Engine (over called as Under Square Engine): The Stroke is "longer" than the Bore.


    >> Engine Character of a Long Stroke Engine: Engine makes good Torque at relatively lower engine revs, good for bikes where good Torque is desired at lower/relaxed engine revs (Eg. commuter bikes, touring bikes)

    >> Eg. of long Stroke India bikes:

    Royal Enfield Thunderbird Twinspark (70mm x 90mm),
    Hero Honda Karizma (65.5mm x 68.2mm),
    Yamaha R15 (57mm 58.7mm) (which is actually surprising for a track oriented bike)





    Square Engine: Engines where the "Bore" and "Stroke" are almost of same size. These engines theoritically seem to balance the best of both worlds.

    >> Eg. of Some "Square Engine" bikes in India:

    Hero Honda CBZ Xtreme/Hunk & Honda Unicorn (57.3mm x 57.8 mm)
    Hero Honda Passion (50mm x 49.5mm)
    Yamaha FZ-16/FZ-6/Fazer (58mm 57.9mm)




    so short stroke engines have high rpm range on their rpm meter compared to the long stroke bikes????

    Quote Originally Posted by Technician View Post
    Just a few facts:

    (i) An engine with less than 1 (bore X stroke) ratio optimises combustion efficiency.
    (ii) An engine with between 1 and 1.2 ratio optimises both combustion and mechanical efficiency.
    (iii) An engine with above 1.2 ratio optimises only mechanical efficiency.

    So, all street engines have a ratio between 1 and 1.2.
    so all superbikes have ratio mare than 1.2 right????

    Quote Originally Posted by Joel View Post

    Now the benefits.
    Short stroke
    1. Lesser piston speed and hence piston wear reduces
    2. accomodate larger combustion area and valves
    3. better higher rpm power
    4. increased engine despite high max revs
    5. Ideal for race engines and fast street machines

    Downsides
    Poor low end torque

    Long stroke
    1. better low end torque
    2. decreased fuel consumption since engine makes low down power
    3. more dwell makes it ideal for forced induction application
    4. most suited for street and highway engines

    Downsides
    Higher piston speeds
    increased wear of pistons and rodswhen pushed
    low tuning potential vs short stroke motors
    lesser valve area and limits potential


    Joel
    what do u mean by the highlighted point??? dwell means wat??? forced induction????
    high piston speeds???? but i thought that the square and the short stroke engines have high piston sppeds for producing more power at high ends!!!
    LosT in TimE!!!

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    Whats the bore /stroke of SHOGUN??
    The Magician"

  10. #20
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    @rennycornellius: Shogun's BorexStroke : 52.5mm x 50mm
    AX 100: 50mm vs 50 mm
    Shaolin: 57.6mm vs 53.0mm

    So I guess AX100 is a perfect square unit.
    Quick Gun Shogun !

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