RhythmRana99

What is the Difference between Short & Long stroke engines?

Sunny

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payeng

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)

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abhichotu.abhi

I am SURPRISED to know that too. Excellent engg.

Taufik

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

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RhythmRana99

thnks...bro

jeyessh

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

Technician

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.

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chicane1879

Nice piece of info!!

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Joel

@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

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