soojy007

Got a generic doubt on revving bikes(say R15, Ninja 250) as opposed against normal bikes(say pulsar 150, FZ16).

I read in threads that the real fun for R15/Ninja begins after xxxx RPM, where it begins to scream(music to ears) and starts to shoot ahead.

I want to know:

(i) what causes these revving bikes to behave so after that certain RPM?

(ii) why does the bike behave normally till that xxxx RPM?.

(iii) why is that normal bikes don't have that RPM range (read as- where the bike switches from normal mode to sports/speed-acceleration/superbike mode)?.

Noor

Query approved

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Samarth 619

Some bikes are tuned in such a way that they deliver more torque in higher rpm's. So, you feel a "push" beyond a certain rpm, as the entire system (engine, fuel system, crank, etc.) starts giving some serious output at higher rpm's, leading to a higher power output.
Like R15 starts pushing seriously after 6000 rpm.

You're probably referring to the YZF R15.

The above tuning that makes it deliver more power in high rpms has a disadvantage- the lower rpm torque gets compromised.

So, at 2000 rpm, Pulsar 150 makes more torque than R15...
But at 7500 rpm, R15 makes more torque than Pulsar 150... All due to this "tuning".

That's why Pulsar's engine is a streetbike, while R15's is of a sportsbike, very generally speaking.

There's no such thing in any bike, called "sports/ speed mode"... Where ever in the rpm range you make torque, you get a strong "push" from the engine.

Enfields give you the push from 2000 rpm itself. All due to their low end based tuning.

See the image below:



Here, CBR is low end tuned and Ninja 250R is high end tuned.
So, CBR makes more torque in lower rpm's but beyond the 9000 rpm, Ninja makes more torque, while both bikes are 249cc.
It's all about tuning and focus (road/ racing).

sunny_

Feels good to see that few bikers are really eager to know "behind the mechanism" concepts..

Nice illustration by the graph.
@Soojy: you see, its all the engine's behaviour. We, humans, can tune it to get the power accordingly in a rpm range. Good luck. Carry on these things. Learn more and more over internet, forums; discuss those things here as well

Samarth 619

In other words, I meant that no such "mode" is activated when you reach a certain rpm.

The modes on these cars and R1 you mentioned are activated by a switch, not by reaching a particular rpm, as Soojy007 was saying...

I mean, torque output maybe low, medium or high. But high torque output at "X" amount of rpm is NOT the result of a riding mode.


And yes, we can use this topic to discuss these concepts... That 2012 R1 topic was not the right place...

soojy007

wow very well described samarth , loved the graph !

the sports-mode i was referring to (what i had in mind) is equal to the "push factor " you had mentioned beyond an rpm (some things cant be jotted down as easy as we speak face to face hence the confusion ;-) )

once again, thanks a lot !

Karthik Mathur (Orange)

Cool topic! RPM has always been something that has intrigued me. Speedo working or not tachometer gotta work for me

btw am i correct to say that when we make the perfect launch of our bike for the fastest possible pick up from it, we should start at that RPM where torque is max and not the power?
ex. in my 220 revving upto 6000 RPM and starting rather than 8500 RPM and starting which achieve better results right?

Honda_CBF

@karthik, yes you're right because torque is the real thing which makes the bike move..
Now, can anyone tell me if its possible to shift the max torque/bhp output of a common indian bike (to any other rpm)??

sunny_

Yeah, that I understand, I just wanted to clarify the topic about modes.

Also, this is the power vs rpm curve and as far as I've looked into the specs of few vehicles(bikes and cars), power may be max @ X rpm, and torque is max at Y rpm. (Somewhere, X < Y and converse in some cases).
E.g. please look for any tech. spec. for any vehicle(say ZMA); power and torque are max at different rpms, suppose torque is max at 7.5k rpm and power is max at 6.5k rpm(or maybe vice versa I'm confused with the exact data)...I hope you know what I'm trying to ask next:
Q.1. Why is it so? Can you relate the two graphs? Why is the power variation different from torque variation?

Q.2. Why is it that after a certain rpm, power starts decreasing whereas rpms are still increasing(that means piston movement right?)? Again, why is that torque started decreasing after 7.5k rpm but power started decreasing at 6.5k rpm only?

Conclusion: I think, we cannot just directly predict about the torque variation from the power vs rpm characteristics; then how to relate these two?

plasmabhai

Ok, so this is what i understand about the whole torque vs power issue. And also this might be a longish post!

Torque is the direct turning force coming out of the engine. The force that any engine can generate to "turn" the crankshaft is called the torque. Its the 'grunt' of the engine. Engine mein kitna 'DUM' hai? Look at the torque figure.

Where does this force come from? It comes from Petrol! And since the energy trapped in the chemical bonds of petrol is finite, that's the max we can extract from it by breaking those chemical bonds of petrol.

So as RPM rises, more and more petrol is being burned and so engine should generate more torque right? Exactly, in an ideal world, but we live in a world where there is inertia and friction. After a particular point, the energy of the petrol gets lost in overcoming the friction everywhere and the momentum of the rotating crankshaft, flywheel etc. and so the torque drops.

Why do different engines have peak torque at different RPMs? That's because of the design of the engine itself! For example, Honda CBR250R has a single cylinder, this means its piston are larger, its flywheel, fatter, heavier than Kawasaki Ninja 250, which has 2 cylinders, therefore smaller pistons, smaller flywheels and engine components of smaller mass. But this also means that in a low RPM, there will be a much HUGER EXPLOSION inside the Honda engine, generating the energy for the bike to leap forward at low RPM itself. That's why its more of a cruiser bike. Ninja on the other hand, with its faster moving lighter engine parts will leap forward only at a higher RPM when MORE NUMBER OF SMALLER EXPLOSIONS are delivering enough energy for the engine to "PULL" the bike. So is Honda better than Ninja? The red line of Honda is nearer 9500 and the Ninja can go right up to 12000, this is because at such high RPMs, the explosion inside Honda's engine will destroy the engine itself, while the Ninja can sustain the explosions since the engine parts are lighter and the explosion more controlled in 2 as opposed to 1 cylinder.

If the peak torque rises and then falls, why does Engine Horse Power keep rising? That's because Torque and HP are related by the formula:

Torque * RPM
Horsepower = ------------
5252


This means, even if torque falls, if the RPMs are rising, power from the engine will keep rising. Infact when the RPM is 5252, the torque and Horse power curves intersect at a point. So why do the Horse Power in Smarth's graph decreases towards the end? That's because the value of torque is now so low, that even with higher RPM value, the power of the engine will only fall. That means that at such high engine speeds, the energy trapped in the petrol is all being used just to overcome the inertia of the moving parts of the engine itself!

All this means, that in a lower RPM, more torque is available for the Honda than Ninja, but the Ninja eventually produces more power since it can go right up to 12000 rpms and so it will be faster than CBR250. So irrespective of acceleration, if the road is long enough, Kawasaki will beat the Honda NO MATTER WHAT!

I ride a Honda Dazzler and the peak torque comes in at 6500rpms, this means that the bike really flies only when I cross 6500rpms. The Yamaha R15 on the other hand generates peak torque at 7500rpms, this means that when i am racing a Yamaha R15, i will have to change gears when i reach somewhere around 6700 rpms while the yamaha will keep pulling till 7800rpms and then change gear! So if the Dazzler and R15 had identical torque, we would accelerate at exactly same rates till I reach 5th gear and 6500rpms, beyond that the Yamaha will just keep pulling the ride into the horizon.

But infact dazzler has a lower torque than yamaha, so yamaha pulls away way before 5th gear, infact in 3rd gear, as i have noticed when i have raced R15s. And why does R15 have more torque plus peak torque at higher RPM? That's because its engine itself is made of lighter parts, higher quality parts, that's also the reason why my dazzler redlines at 9500 whereas R15 redlines at 11000.

All this said then can you not change the raw torque and the RPM where peak torque comes in?

To answer Honda_CBF's question, yes you can. 1) By structurally changing the engine parts. That's what Joel does, he changes the pistons and the flywheel, and eventually that's what results in better performance, because changing these components shifts the peak RPM.
2) If that is the case then why does Joel bother with big bores? Because big bore means the raw torque figure increases. This happens cause more petrol can be burned so more available energy, more grunt, more dum! So Joeling your machine leads to higher torque figure at higher RPM. So if you can burn more petrol you would get more torque! And that's what happens in Turbo charged and Supercharged engines. Because the air can be compressed, more petrol can be mixed with it leading to more available energy to move the vehicle. And that is also what happens in NOS systems. The high amount of available Oxygen combines stoichiometrically with Petrol leading to insane amounts of torque. Infact NOS is only limited by structural integrity of the engine, too much and the engine will actually explode!

This also explains the various "modes" in bikes like R1 and supercars like Audis and Ferraris, the button helps you choose between various settings of ECU, so u decide the amount of air-fuel mixture going to the engine and the eventual grunt! Thats why Joels ECU reprogramming is so hot..!!

This is also why playing with upjetting carburettor and high flow KnN air filters betters performance, cause it changes the absolute torque figure of the bike, not the peak RPM. Ofcourse most people who dont understand much just buy some KnN and do some random upjetting, but thats actually busting up you bike, not modding it!

Also I want to put in a disclaimer, all of this that I have written are things which I have understood after reading up a lot. Also I don't understand a lot of physics that go behind engine dynamics, I infact am just a plain old biologist doing his phd! Also, I have never seen joel, nor seen any of the bikes he has joeled and thus I may be wrong where-ever i have taken his name, though IMHO i am not wrong there. But thats what am supposed to say here cause this is a disclaimer!

Goto this link for understanding in more detail:

http://www.vettenet.org/torquehp.html