I am a little confused. Isnt Bore > Stroke called as oversquare engine?? Stroke ratio - Wikipedia, the free encyclopedia

Let me see if i can help you out with this query.

The general perception of people is that Power is 'Dum' or 'Shakti' or 'Force'.
In engineering talk this is incorrect. The 'Dum' is called 'Force' or more broadly defined as 'Stress'. But lets not go so deep, we'll be sticking with Force for now.

Now this Force is a vector unit, which has a 'linear' direction (*the direction of Force passes through the centre of gravity in atleast one c/s plane*). It moves in a straight line.Now when this Force is applied to an object at a tangent, then the force is multiplied by the lever distance and this 'new twisting force' is called Torque.

Torque is the force that (turns the wheels and in turn,..) propels the vehicle forward. Which with the help of speed reduction i.e torque multiplication, shifts the weight of the vehicle overcoming other resistive forces like, rolling resistance, wind resistance, friction in drivetrain, etc.

Power is a quantitative unit which is used to describe how much 'force' or 'torque' a machine/or device/creature/whatever can exert during the time span of a second. or in special cases during a period of time. In other words its a indicator of how much work it has done.

eg: If i am a quarry worker. I have the physical strength (force) to shift , lets say 20kgs of ores. and by the end of the day i have shifted 2 tons of ore. The 2 tons of ore is my 'power' i.e i have that much energy, which i convert into force to shift 'n' tons or ore in a specific time period of a shift/day or over time. (not the salary 'overtime')

So Torque is Force, and Power is a accountant's log book of how much Force is used (and energy spent) in a specific duration, (conventionally its per second for automotive engines)

Torque - Kg.m or N.m or ft.lb or J/rad
Power - Kg.m/s or N.m/s or J/s or W or hp
(Kg and lb are kg.f and lb.f)

EDIT:
It seems that I have made a booboo , though i still have my suspicion regarding whats on the net, But untill i can find the correct definition of what is a under-square / over-square with regards to bore/stroke or stroke/bore on paper, I am to stand corrected by Wikipedia and i have made a error of misplaced names.

EDIT2:

Confirmed it with my books, I am sorry, harishkumarko, Adarsh_Bk you guys were right with the names. I called a Bore > Stroke undersquare, wrongly, it is oversquare and the other is undersquare. The dimension that changes is on the horizontal axis not the vertical.. I put undue blame on exam stress, what else. xD er yea I apologise for my error in earnest, and more importantly thank you for pointing it out.

I'm sure he will be even more confused now. I request the interested ones to kindly go through this thread, page by page and post by post http://www.xbhp.com/talkies/pit-stop...at-torque.html

Next, if you want to read more, guys come on you have Google which covers almost 7% of the entire Internet...you can go and search things there. And trust me you need not be a technical guy to understand these basic things. These are very real and once you visualise the things and "relate" the theory with the real scenario you'll start predicting whats going on there inside your engine and you'll start getting the grasp. I'm still a learner though and whenever I get time I try to learn more and more, although my field is CSE

One more interesting link covering basic things here, given by my favorite senior of xBhp PSR Sir, its HowStuffWorks "How Force, Power, Torque and Energy Work"

Now that somebody else is doing the explaining, I must get my doubt cleared. What I understand is, all an engine does is make is Torque. Power is just a product of 'where' in the rev range it makes how much torque. Thats the reason we find regardless of where in the rev range the engine makes torque or even the bore/stroke ratio, engines of similar cc make similar torque.

eg. ZMA -> long stroke engine, makes almost same torque as P220 (both 22xcc) -> short-stroke, Power difference is a good 23%

Unicorn/Dazzler/Hunk/Extreme/P150(all 150cc) makes almost same torque as CBR150R -> radical short-stroke

Discover 125 and 125ST have power difference of 2PS(almost 18%) but same torque.

Duke 200, Pulsar 200 DTSi and Pulsar 200NS make *almost* similar torque at different RPMs though power outputs are drastically different.

Even the Pulsar 180(UG3) and the RTR180 make almost similar torques though their bore and stroke may be different. (God knows why BAL reduced the torque in UG4)

Taking this concept up a notch, even the radically different 134 Ps Kawasaki ZX6R (66.7 Nm) and comparatively much conservative 72.1 Ps Ninja 650R (64 Nm) make almost the same amount of torque. The power difference here is staggering 85%!

And believe me I am not making this up but:
the 210 Ps Kawasaki ZX10R and the 138 Ps Kawasaki Z1000 (both 1000cc 52% power difference) make 112Nm and 110 Nm of torque respectively.

All this makes me say, no wonder the elders said that 'There is no replacement to displcament'.

Anant sir, you are spot on regarding the relation between torque and power.

And an interesting way to look at the torque output. makes my defunct mathematics's part of my brain to work, It has a fascinating depth to it,

I am making a wild guess here this time, on one side the torque can be similiar because, ideally the fuel used is the same, i.e the calorific value of the fuel is the same. and the thermal efficiency of most engines are similiar, so the torque should be similiar too. and technology is more or less similiar.

But on the other hand, the crank size being different could affect the force to torque conversion. the calorific value of the fuel is one thing, and calorific value of the charge is another thing to look at. can we generalise thermal efficiency? there are engines having 24~33~50% thermal efficiency, marine engines like this behemoth Wartsila Sulzer RTA96-C - Engine

and to think about how flow of gases and compression affect the combustion efficiency, and how that would affect the torque?

Too many variables to look at, i for one will need time,.. are you holding back on something?

one more question if Engines of similar cc make similar torque, are they doing that having similar torque distribution? or do they vary quite a bit?

Another good example would be Royal Enfield's machismo 500 and classic 500,machismo makes 23.6bhp and 40.85nm torque while the classic makes 27.2 bhp and 41.3nm torque(good difference in power but almost identical torque figures).

Since everybody has provided the technical viewpoint i will not get into it. I will explain it in layman point of view.
Usually three things are there in an engine. They are displacement, torque, power.
Displacement- The amount of piston travel in an engine.
Torque- The pulling power of an engine.
Power - The ability of an engine to maintain its top speed for long.
Displacement and torque are directly related. For same displacement you can increase the power but increasing the torque is not possible, if done only slight increase in torque.
Regarding a RE classic and p 220 first let us look at the specification-
Re classic-
Power- 27.2 bhp @ 5250 rpm.
Torque- 41.3 Nm @ 4000 rpm.
P 220-
Power- 21 PS @ 8500 rpm
Torque- 19.12 Nm @ 7000 rpm.
Now look at the difference in rpm. You will see that pulsar makes power at 8500 rpm which the 500 will never be able to attain so by default 220 will rev more so it will reach greater speed. So it will in theory reach higher speeds but since it lacks torque it is short geared to pull in gear. The pulsar has to rev in order to reach pull decently.
In case of 500 it makes it power at only 5250 rpm at which the 220 will not have reached its maximum torque but by that time 500 has already reached its colossal 41.3 Nm of torque, so by default it will not reach much top speed as it doesn't rev much. But due to its colossal torque it is tall geared so it reaches a top speed same as 220.
But the difference is that although both reach same top speed the 500 will be much relaxed than than the 220.
Let you ride both the bike in hilly region or in traffic area you will see that you will be busy in shifting gears on pulsar while on 500 you will be chugging in 4th or 5th without any gear change.
Scenario 2- You can race with the 500 on 220 but run both the bike at 120 kph constant for every day and see how many km 220 lasts and the 500. The 500 will last almost double the distance than 220 at that speed.
Its like comparing a car to train. Although a car can run at 140 kph and accelerate much swiftly than a train but try running the car at 140 kph for 20 hours a day as a train does and see that the train will last for years and the car probably a month.
So a engine with bigger displacement will be much relaxed than a smaller displacement so it will last much longer than smaller engine so the saying is true- " There is no replacement for displacement".
And regarding the torque think of an experiment-
Try to pull a car like indica with both the 220 and 500. Now you can feel the difference between 19.12 Nm and 41.3 Nm torque very easily. It is a simple fact that the 500 will pull where the 220 will never imagine because of its torque. And remember Torque can be multiplied by gearing but power cannot be.

Given explanation is justifying very well about the concept and the difference in very simple words, anyone can understand it very easily...
The most informative topic for me...will read it many times, to understand the every point...

Can someone rename this thread :P

Torque - What moves your bike
BHP - What keeps it moving


As a thumb rule, the larger the piston, the more the torque.

if Engineering is what matters ...

the RE c5 has 27.2 bhp which is maxed in 5250 rpm which is at a mid rev range
27.2 hp must do a minimum of 140 + ...
if so where is the power lost or transfered ..

and as all say due to more torque the bike acclerates faster hence at least its 0-60 must be faster right?! ,, due to its power / torque and a 500cc engine ...

i accept the engeeering and base of the model is totally different ,But the query is where is the power lost ??

well the 350 cc RE and 500 cc RE have similer top speeds just with a difference of 10 - 15 kmph ?
350cc - 19.8 hp
500 cc - 27.2 hp
where is the use of the 7.4 hp ? what is the reason behind the heavy loss of its power in top speed ? is the 7 hp just for 10 kmph increase that too with vibes

sorry i have a lot of question but this is what i mainly wanted to clarify ... well i am a fan of RE mascular looks and obviously love top end speeds ..

Good question I were also gonna ask this....

You should now introduce two new variables in you understanding.
Weight of the bike, and Gear ratios.

We already covered bike weight here at #1.
And as for gear ratios, not all of them would be needed, just the top (rarely top-1) gear would be enough. That IMO is the easiest to change on a bike (by sprocketing).

By #3 I mean aerodynamic drag. Which has a huge influence on what top speed can be achieved. Ask Xionite what plonking an R15 fairing on a P180(UG3?) does to its top speed.

@Satyen Please also explain the thumb rule you mentioned.
Use examples if you want .

like following 6xx cc bikes
1cyl: 67 Ps KTM Duke 690
2cyl: 72.1 Ps Kawasaki Ninja 650R
3cyl: 113 Ps Triumph Daytona 675
4cyl: 134 Ps Kawasaki ZX6R

Which one *should* have the highest torque as per your thumb rule?

Pardon me sir. But my post was a reply to the someone commenting on the 350 vs the 500 (vs the P220)
You missed the point by a fair bit there, and more so with the thumb rule.

duke 690 - Single cylinder 102mm - 67nm torque
ninja 650r - twin cylinder so 2 x 83mm - 60nm i.e wanna assume 30nm per cylinder?

Want more?

is it just me, or everybody else also feels that suddenly xbhp has become very lively in certain threads, since last couple of weeks.
i am njoying it.