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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 bikeswhich is actually surprising for a track oriented bike)





Square Engine:

I am SURPRISED to know that too. Excellent engg.

great explanation bro . .. no wonder why Naked Version of R15 - FZ 150i (57,0 x 58,7 mm) is good for comuting ride

thnks...bro

thanx bro....now i ve got the clear idea...

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.

Nice piece of info!!

@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.

The p220 is not a short stroke engine since it has a larger bore. There is a thumb rule that an engine is regarded as a short stroke unit only if the stroke is around the 50mm mark. From SBKs to an F1 engine, the stroke is under 50mm and they are real short stroke engines.
Now an engine with a 100 x 80mm dimension is still not a short stroke engine.
FYI, karizma has a 66.2mm stroke.
Most makers consider engines within 1.5-2mm tolerance as a square engine.

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 rods when pushed
low tuning potential vs short stroke motors
lesser valve area and limits potential

However in some cases, engines tend to show a different character courtesy the setup. Some long stroke motors seem like short stroke and vice versa. The point is how well the manufacturer has designed the components and optimised the package. The karizma revs better than the short stroke CBZ(both are identical engines with only stroke change) and the R15 behaves like a short stroke engine with a peaky power band courtesy the ports and cam. So the overall engine feel is left to the judgement of the maker.


Joel

^^Awesome information about the engines.

...and this was news to me!!

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.



Had no clue about that.. can I get to read more about it somewhere?

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

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.

@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.