May 9, 2010

20 What is a Long Stroke / Short Stroke Engine? Which is better?

What is actually a Long/Short (Under/Over Square) Engine? How do they differ in engine characteristics?

I clearly remember that when the TVS Apache RTR 160 was launched in 2007, TVS made sure to highlight (at least in the print media) that the engine of the RTR was an "Over Square" one. But there was never a proper explanation of what the term "over square" engine meant or what exactly was it's benefit for the rider.

Bore x Stroke

Let me try to explain these terms in as simple English as possible.

The engine size along with the cubic capacity (cc) is also specified as "Bore x Stroke" dimensions of its cylinder.

Bore: The Diameter of the cylinder block

Stroke: The Depth of the cylinder block







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

Engine Character of a Short Stroke Engine: Due to the relatively shorter stroke, the engine revs fast and is good for bikes where fast build up of power is essential (eg. Race/track bikes, Supersports bikes).


[Update 29,Oct 2010: I have recently learnt that for an engine to be termed as "Over Square", the ratio obtained by dividing the numerical value of the Bore by its stroke, should be around 1.2 (plus - minus a few decimal points is considered o.k)

In which case the Apache RTR 180, Pulsar 150/180/220 would not qualify as ones with over square engines, as posted previously.]



"Short Stroke Engine" bikes in India:
  • Apache RTR 160 (62mm x 52.9mm)




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

Engine Character of a Long Stroke Engine: Due to the longer stroke, the engine makes good torque at relatively lower engine revs. It is good for bikes where torque (pulling capability) is essential at lower/relaxed engine revs (Eg. commuter bikes, touring bikes)

Some "Long Stroke Engine" bikes in India:

  • Royal Enfield Thunderbird Twinspark (70mm x 90mm)




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

[Update 29,Oct 2010: I have recently learnt that an engine to be termed as "Square", the ratio obtained by diving the numerical value of the Bore by its stroke should be around 1 (plus-minus by a few decimals is o.k).

In which case the Apache RTR 180, Pulsar 150/180/220 qualifies as ones with "Square" engines, and not as "Over Square" engines as posted previously.]



Some "Square Engine" bikes in India:

  • Hero Honda CBZ Xtreme/Hunk & Honda Unicorn (57.3mm x 57.8 mm)


  • Yamaha FZ-16/FZ-6/Fazer (58mm × 57.9mm)


  • Apache RTR 180 (62.5mm x 57.8mm)


  • Pulsar 150 (58mm x 56.4mm)/180 (63.5mm x 56.4mm)/220 (67mm x 62.4mm)


  • Hero Honda Karizma (65.5mm x 68.2mm)


  • Yamaha R15 (57mm × 58.7mm)





Which kind of engine one is better?

Well, it depends on what type of rider you are.

If you are of the sporty tyre and like to rev the engine hard, "Over Square / Short Stroke" engines should rock your boat.

If you like your bike to have good pulling ability at low engine revs or if you have to carry heavy loads (maybe a heavy pillion), then "Under Square / Long Stroke" engines should be ideal for your needs.






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This is to remind that the Views or Opinions in the blog are entirely mine unless explicitly stated. The Views and Opinions published in this blog should in no way be related to any other person or organization associated -- directly or indirectly -- with me.







20 Comments:

Akash said...

Wonderful explanation once again. thanks

Sajal said...

Really very understandable and simple explanation :)

Payeng said...

Thanks guys

abhiram said...

thanks for the simple, logical explanation....i wasn't sure about this...it cleared my doubt..

Mithun John Jacob said...

Excellent lucid explanation !

Sajal said...

For the R15 being Long Stroke..... may be this was the reason both of us found the R15 sluggish at lower RPMs and the bike failed us to give the chills like our Pulsar does!! But really I'm surprised as to why the R15 has a long stroke engine, while the '09-'10 R1 has the shortest stroke engine in it's class!!!

Payeng said...

Thanks again guys.

@Sajal, I guess the long stroke on the R15 was done to provide better torque at low revs, but I guess (my assumption) that the 4 valve set up on the R15 and the bid to make the bike high revving made it a bit sluggish at low revs.

Gautam said...

Good food for bikers mind! Thanks.
But let me explain, as short stroke piston has relatively more (vertical) movement than long stroke for same revolving of crankshaft, do it wear is (atleat for theory) more?

Payeng said...

@Gautam,

Wear and Tear would depend more on the quality of manufacturing and the quality of materials used. For eg. modern Super Sport engines are extremely high revving.

Moreover a lot will depend on how the engine is (ab)used and how well it's maintained.

Siddharth Soni said...

Thanks Payeng. Keep explaining. Helps :). Have been riding bikes but just failed to make sense of such jargon splashed all across in magazines, etc. unless someone explained.

Good job.

You need to rectify this error in comment-numbering.

Car Games said...

Thank you for the informative article.

lalit nagarth said...

i am particularly surprised by r15 being a long stroked bike ,
may be this is the reason it isnt able to beat 220 in straight line run .

Anonymous said...

thaaaaaaaaaanxx

Anonymous said...

thaaaaaaaaaanxx

lalit nagarth said...

i am particularly surprised by r15 being a long stroked bike ,
may be this is the reason it isnt able to beat 220 in straight line run .

Gautam said...

Good food for bikers mind! Thanks.
But let me explain, as short stroke piston has relatively more (vertical) movement than long stroke for same revolving of crankshaft, do it wear is (atleat for theory) more?

Mithun John Jacob said...

Excellent lucid explanation !

saurabh said...

thnkx 4 updatin me........keep writing ur posts.....u made me a regular reader

Rakesh Ravindran said...

that cleared my doubts,does that mean long strokers are high revving engines,that is they have to be revved high to get the optimum power?

Sharon SL said...

So my Herohonda CD Deluxe is Square engine??
I think over square engine's hav low CC ..,because it's stroke volume will be less.Also has less Compression ration.

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