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I really want to see what the others feel about this topic before I make any comment. For now, I will stick to 'There are advantages and disadvantages of both' .

I think bigger cc engine won't be stressed at prolonged ripping comparing to smaller cc engine with same power deliverance.

Re: Same power, different cubic capacity - what's the catch?

Stress is relative. Just because an engine develops higher power doesn't necessarily mean it's more stressed than the other. The way the engine is built and the quality of components being used ,play a major role in how the engine handles the different forces and loads. If the engine is made from quality materials, and good manufacturing process is followed, I don't see why an engine developing more power can be called "stressed"'.
At the end of the day reliability is what is required and that's where this discussion is eventually going to lead to..

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The bore and stroke of both the engines makes the difference, wont it ?

Nice query.
I also feel that it's somewhat related to the stress ON the engine for pulling loads and running.
R15/Apache 180/Karizma - all have 17 horses to claim, but I feel that the extra displacement helps the Honda engine run smoother with relatively less stress.

Advantages - Relaxed engine, prolonged life, much more torque, (a little) higher fuel efficiency in its class.
Disadvantages - Way too many. Less power being one of them.

Well, with a bigger engine you get more torque, as in the kick you get when you open the throttle. Extracting similar power from a small engine compared to a bigger engine , [take for example the the Karizma and the R15] will need you to dial in higher revs for the smaller engine to get significant chunk of power. Whereas, for the Karizma, power is available in a wide band of revs. This also means you need a significant over rev most of the times. R15 revs a full 2500 rpm more then a Karizma.
The exact difference will lie in speed. If the R15 were to make even more power than Karizma,[say 20 bhp but with same torque] she would have roll on[in gear acceleration] more or less the same as the 17 bhp R15 but a significant advantage on the top speed front over Karizma.
In short, you would lose out on torque if you are extracting power from an engine similar to an engine of higher capacity. All the difference lies in torque. While, with a bigger engine, you would lose on fuel efficiency a bit.

[All these are my conclusions drawn over from extensive rigorous thinking and posing questions. These might be wrong. Folks, you are welcome to enlighten me further if I am wrong somewhere]

Just the bhp produced at crank will not be indication of performance, The on road performance depends on lots n lots of other factors too like torque, gear ratio, transmission losses, rolling resistance, weight of bike, faired/naked, tuning of the setup (meaning if setup is peaky) etc. Its a big topic to discuss
As the saying goes "There is no replacement for displacement" it holds really good on the drivability part of the machine, A bigger engine which produces lesser bhp would still produce more torque naturally due to displacement and this shows in the way it drives. A peaky setup will have its lower end drivability affected but will easily out-perform a bike of similar cc's or even a higher cc bike at higher revs.
To draw an analogy, try the R15, below 3k you'll really feel that the power is as good as a 100-125cc bikes, but cross 7k rpm and the story changes completely. On the other hand ride a bullet, the way it picks up speed is effortless, throttle need not be wringed at all. It acclerates with just 1/2 the throttle with greater pull than other bikes at full throttle and you'd feel that this bike would cross even 160kmph mark easily, but truth is it cant!! Try and hold that throttle till full revs and tadaaa.. nothing happens.. progress is very linear and it just feels very lazy. Its a torque machine and is designed to cruise not for speed.
Same is the case with Zma and R15, Though on paper both of the produce about same power. Zma needs little effort to accelerate from stand still and also the way it picks up speed will be very effortless compared to R15. On the other hand the R15 requires skills, keep the R15 in power band and it can out accelerate the Zma very easily. The power band on the peaky setups (lesser cc bikes with more power than its counterparts) will be very narrower.
Same is the case with duke and cbr 250, though both of them produce about same power on paper - more torque, fairing and good gear ratios work the way for cbr to out perform duke.
Same is the case with Innova and ertiga (both diesels) in car world, Innova has excellent drivability at any revs owing to its larger displacement engine.

So the catch is in drivability, a bike with more displacement will be excellent to drive around in all conditions n picks up speed with lesser effort as it'll produce more torque at same revs compared to a bike of lesser displacement.

The catch is that the BHP equation is always incomplete without the TORQUE & R.P.M. There are factors like kind of engine i.e number of cylinders & their configuration, bore & stroke, material used, number of valves, spark plugs, SOHC or DOHC, CARB or fuel injection, EXHAUST type, Air ram induction etc. As you can see rest all the factors are depended either on intake manifold or on exhaust manifold. So the importance is how we get that power & torque, which separates cruisers, sports bikes, street bikes from one another. This is a very deep concept & my above lines don't even qualify for its outline.

Re: Same power, different cubic capacity - what's the catch?

Wow! this seems like a pretty vast subject. All this while I was going by the fact that the r15 is for track, RTR is for street and zma is for touring.

When torque comes into the picture, I'm guess the stroke length plays a larger role than bore dia no?

So baseline is that, a larger capacity has better drivability, in other words puts in lesser effort, right?

I see that a lot of variables are added - build quality, intake parameters, exhaust parameters and all... I really don't understand all of that. But, I'm guessing that by making extensive changes to multiple parameters, the drivability can actually be resolved for a peaky setup. Correct?

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Exactly the question runs in my mind, but never got correct word to define it ... waiting for Antz post bye the way .. and I seriously want a good conclusion of this topic rather then just a infinity drag Race


All I can Say its Relation of Torque & Power... Power may be of how fast the engine works in terms of rpm & Torque is something a force which causes movement or displacement....

So the peak power of 17bhp for Karizma is in different RPM then RTR, bigger power mean faster & stable engine work at uphill, against cross winds & at time of acceleration (here faster doesnt mean better pick up though).


The difference may be clear by this stats ...

ZMR generate peak power of 17.6bhp at 7000 rpm whereas the peak torque is 18.35 Nm at 6000 rpm.
RTR generates maximum power of 17.3 Bhp at 8500 rpm, with a peak torque of 15.5 Nm at 6500 rpm.

@Shahbaz Well the answer to your query lies in a simple exercise. We have been discussing quite a lot of stuff which ideally could have been easily avoided using this simple exercise.

To understand the catch, we must understand what will happen if we happen to swap the engines on bikes with identical power outputs.

So, as a test case, we assume that we, keeping ALL other things (like weight, aerodynamics, tyres, rims, gearbox etc.) constant, somehow succeeded in swapping the engine from an R15 with that of a Karizma R and vice versa. (Pick CBR250R <> Duke 200 or Unicorn <> P135 if you wish, doesn't make too much of a difference)

Based on the facts/observations we already know (from spec sheets, reviews etc.), how should the engine swap affect:
1. Theoretical top speed (Speed at redline in top gear) ?
2. Initial Acceleration ?

What simple non-engine-related modification can bring the above mentioned performance parameters closest to stock even after the engine swap?

P.S.: To keep the calculations simple for now, lets initally ignore parameters like torque curves, crosswinds/headwinds/tailwinds, intake/exhaust manifolds, bore/stroke and the no. of valves for the purpose of this exercise.

IMO, nothing. ZMA is 20 kgs heavier than R15. Even if i remove the mud guard, engine cowl, saree guard, chain cover and change sprocket config, nowhere am I getting that stock ZMA performance.
The R15 would, on the other hand accelerate like crazy and there may be an increase in the top speed due to a better aerodynamic fairing (this increase is w.r.t ZMA top speed, not R15's).

Contrary to what you said, in the scenario I just described, the theoretical top speed of the ZMA-R will increase and that of the R15 will decrease. Allow me to explain how.

A stock Karizma is geared and sprocketed to reach its *theoretical* top speed at its 8500RPM redline in 5th gear
If instead it gets a R15 engine alongwith the exact same gearing, it will now reach its *theoretical* top speed at its new engine's 10000RPM redline in 5th gear. This means, in a zero aerodynamic drag scenario, a R15 engined Karizma will reach a 17.64% higher speed at redline in top gear compared to a stock Karizma. But as you correctly said, since the R15 engine makes less torque than Karizma, though it can theoretically reach a faster top speed, its acceleration will suffer.

Conversely, the R15 can now only rev till 8500 RPM instead of 10000 RPM redline of the stock engine and so will reach a 15% lower top-speed than a stock R15. Even though, given other factors, it could have reached a higher speed using the same amount of power, the engine hit its redline and the bike couldn't go any faster. But once again as you correctly said, since the ZMA engine makes more torque than R15, with its new engine, the R15 accelerated like crazy and hit the redline in 6th gear very fast but just couldn't match the stock R15's top-end.

Now tell me how do we *theoretically* get as close to stock performance as possible using a non engine related mod??

Hint: Just 2 pieces of metal have to be replaced in either case. Mod Samarth is the best person here to answer this one but I'm not sure if he is reading this one.
Trivia: The only bike made in India which hits its revlimiter (not just redline) in top gear in stock form is the KTM Duke 200.

LMAO.
Throw in the Humble 500CC engine from the Classic 500 into this argument please. Pretty please!