Friends, my two cents.

Stress is simply nothing but the load on the engine and the parts. In pure technical terms, force per unit area. More power- more forces- more stresses.

We I guess are talking about the strain on the engine. Strain on the engine depends on the stress acting and the stress that it can take up. Now the strain on the engine is dependent on the stress but there is again no way to identify how much the engine is strained unless we know the design factors as to how much each part is designed to deal with.

Now Mean piston speed is an important indicator of stress on the engine components but not the ONLY one. Another important aspect is the peak pressure. Engine power is closely linked with the peak pressure within the cylinder, any increase in the power has to see an increase in the peak pressures. Along with the Mean piston speeds, it is the peak pressure that stresses the engine. Everything from the head to the crank has to be evaluated for being able to take up this increased load.

If it is indeed a rebored 125, I doubt how much more it can take. Of course all the critical parts would have been strengthened already to take up the load of a 25 Bhp engine, but then how much more? is the question

I am not that much informed, but the posts in this thread has been very educative.

Anyways from the numbers posted by @antz.bin, I can relate to a keen observation..

I see that P220 engine, sounds VERY harsh after 2-3years of ownership, whereas I have never heard any R15's engine note like that. So, It look like P220 can't sustain the the extreme Ripping because of it's higher MPS, while R15 can easily sustain the high MPS due to it's Forged Pistons, and other stuffs.

Please elaborate .
Do you mean to say:
1) A generic bike engine running at 7k RPM will be more stressed in 1st gear as compared to 4th gear. (i.e. shorter the gear, higher the stress)

OR

2) A generic bike engine running at 7k RPM will be more stressed in 4th gear as compared to 1st gear. (i.e. taller the gear, higher the stress)


OK, my bad, . What you were saying and what i understood were entirely different.


On a different note though, The Honda CBR250R runs a longer stroke (6mm more) and bigger bore (4 mm more) than the Duke 200 and but still has a redline of 10500 RPM (= Duke Rev Limiter).


Even though conventional wisdom would say that short stroke engines are easier to rev higher, here is a comparatively longer stroke motor which is supposed to rev higher. Does Honda have excess faith in god ?

Maybe the cut-off was kept at 10.5k for Duke just because it wouldn't have been able to clear BS3 emission norms (which are stricter than Euro 3) had the cutoff been moved to 12k instead. We must never forget that the Duke 200 sold in the UK is rated at 27 bhp whereas the Indian version does just 25 even though both are made in Chakan!

Since bike modifiers don't care a rat's behind about the environment when they use ffe and big bores, Why would they care about a mild revlimiter? No wonder the ECU remap for Duke was the very first mod available for the bike. A mod which promptly removed the 10.5k revlimiter and moved it up to 11.7k RPM. All within 1 month of Duke 200 launch.

Nothing much to say, Just one straight answer, if you calculate the gear ratio and sprocket combination used in CBR 250 with that or CBR 150 or Duke 200 you would never quote this as an example. The chassis and gearing is as such that CBR 250 is not meant for the tracks or hard revving

The least you could do is answer the 1st question . What we are discussing here is engines and not chassis, frames, rims or tyres.

Bro, I seriously don't know why you brought the CBR 250 boreXstroke has brought into comparison for that of a Duke. If you compare the engine block then what about the big case below it? Even R15 and GS150R have similar blocks. Is XBHP short of experts? I am sure there should be a guru above you in XBHP moderators list and pls show him the above 2 comments and I am sure he would guide you appropriately...

Lets talk about the point, my views are "Duke 200 may not have much of juice left for aftermarket modds" and re boring is not possible for the Duke 200 until it appears in the middle-east market.

Note: I am just a 2nd year graduate in XBHP and I know a few who have done their PHD in XBHP.

The gurus above me in the Moderator's list may or may not be more technically inclined than you are, but still how can they know what is in your mind. I apologise for the fact that I always have trouble comprehending what you post, it is my own weakness and I am extremely sorry about it. But once again, How would the PHDs of xBHP know what *YOU* meant by the following statement?

Just forget about the analogy with CBR, reboring, increasing rev-limiters and answer the simple question in KBC style.

Do you mean to say:
a) A generic bike engine running at 7k RPM will be more stressed in 1st gear as compared to 4th gear. (i.e. shorter the gear, higher the stress)

OR

b) A generic bike engine running at 7k RPM will be more stressed in 4th gear as compared to 1st gear. (i.e. taller the gear, higher the stress)

OR

c) Something else.

"C"

It depends upon the gear combo, coz a drag spec is opposite to a track oriented bike. But still my point is that the engine is stressed differently in each gear depending upon the power extraction. I did read a few articles and and ask a few experts but honestly still not able understand the mean-piston speed concept w.r.t engine stress (Is it the same for all gears?)

Thanks for the answer. Though it is still vague and has no fixed formula to estimate the amount of stress on a CBR150R engine as compared to an R15 (same displacement, similar power, drastically different designs).

Yup it is the same for all gears... if you can somehow rev an RE to 7k RPM even in neutral or any gear from 1st to 5th, it WILL KILL THE ENGINE!! INSTANTANEOUSLY!! Thats the reason you just cannot do it using the engine's own power, rev-limiter or not.

This is the only way I have found to rev an engine to an RPM more than its physical capability to handle revs. Doing this will seize the pistons even if there is absolutely zero power being produced (as can be evidently seen in the video).

PISTONS @ 10.000RPM - YouTube

P.S.: You need not remove the head , that was done only for demonstration purposes.

Damn! Just when the discussion (read: argument) was getting interesting you post the above.

Boo!

Will have to believe the mean piston theory even now. Blasphemy!-.-

Highlighted Part: isnt that what Antz.bin said citing the example of a ZMA on why it lasts longer (cuz its rev'd much lesser) when compared to a P180 (whose bones are ripped to glory)...Antz.bin?

Again we are missing something very vital, the difference between engine output and power delivery

The answer from your question is in the question itself, Let me rephrase your question, how come R15 is able to produce maximum power at 8500RPM and CBR 150 at 10500RPM?

Ok I hope the thread is deviating, lets stick to the point.....

Two Questions:

*if the MPS of R15 at 'red line' is 19.xxm/s then what is it at 'rev-limiter'?

*how does one calculate it? If this isnt possible for someone seated on his sofa before a laptop then I guess its pointless repeating the above for a Duke.

Naah, that was definitely not my question. I well and truly know HOW and WHY those 2 phenomenons happen.

My question is, using your formula or perception or thought process or whatever, could you please give me a definitive answer to the following question: Which bike's engine is more stressed at its peak power RPM when going constantly at that RPM for say 10 minutes. R15 or CBR150R? (Assuming quality of components used on either bike to be similar)

Believe me, we are all trying to learn, and on taking this forward, this will definitely be very much on topic.

The formula is very simple:

stroke * rpm / 30 = MPS in mm/sec

• we are deviating from the topic.
• @antz : your video does not show anything, it just shows that when an engine is driven beyond revlimiter range, it blows up. now this is a fact everybody knows.
• we are not discussing what happens to an engine when it is driven beyond rev range, we are discussing whether a Duke200 engine is comparatively more stressed or nnot.
• iin the video, the guys have removed the head of a LC engine, bravo....no cooling, no lubrication. what else do you expect.

EDIT:

CBR250R produce a peak power of 25bhp at 8500 rpm, so at peak power, its MPS=15.583 mps

for a KTM Duke200 to produce same amount of power i.e. 25bhp it has to got to 10000 rpm =16.333 mps

so, to produce same amount of power by a lesser capacity engine, here- duke200, its engine is more stressed, even by MPS theory.


now don't kill me for making a generalized statement, i made it because we are mainly talking about duke200 and it being a stressed engine because it produces a power equal to a bigger engine say CBR250, now CBR is used, because in terms of technology, it is the only bike available in india, comparable to duke.

now lets talk speed.

CBR250R does a 136 kmph at 8500 rpm in 6th gear.

now, duke200 does a 136 kmph in 6th gear at somewhere between 10000 - 10500 rpm.

so again to maintain same speed duke200 is more stressed even by MPS theory.

@Antz: see with your help even i am getting better at numbers...now i am down with viral fever, and only this calculation kept me awake till this time. going off.

Now, do you agree, that Duke200 engine is comparatively somewhat more stressed...??

Edit2: bro, did i just saw your reply, and then it was removed without a trace....i think i did. never mind.

@Prince Actually I was mightily pissed after reading your post prior to the editing. But now that you have put genuine thought and effort into the post, I am most definitely not. Also since you have backed up your hypothesis with actual numbers, it is no longer a vague generalized statement (which would have otherwise attracted scrutiny )

Anyways, I do agree that Duke is more stressed at 'peak power RPM' than a CBR250R. I never argued with that bit. (Thats the reason we recommend CBR over Duke for long distance touring on 'What bike' threads )

But still, the fact remains, that each manufacturer decides on a suitable redline and revlimiter after looking at various factors (like branding, emissions, cost savings, intended usage, pricing etc.) and not just by looking at the RPM the engine will blow up.

And what this theory also tells us is that the Duke has much more upgrade potential to be unlocked by simply upping of the the rev-limiter than, say, a CBR250R or an R15 which are much more stressed at 'Rev-Limiter' ! Isn't this exactly what I posted in post #2 of this thread?