Discussion Approved

Actually I also had this question for a long time. As for your query, Adding the KTM 200cc (24.67bhp OR 18.4kW) engine to the existing comparo between CBR250R(25bhp OR 18.7kW) and Ninja 250R (32.18bhp OR 24kW) , if we look at their power/liter we get the following numbers.

Kawasaki : 128.73bhp/liter
KTM : 123.35bhp/liter
Honda : 100bhp/liter

From this, we can see that the Honda 250cc engine is in fact a very mildly tuned powerplant and realistically a street-legal 250cc single should be capable of a lot more power (as amply demonstrated by the KTM) since all 3 have been tuned to work on the petrol available in the same country adhering to the exact same emission and sound norms.

A continuation of this however would be how different no. of cylinders on bikes with different cc can all be classified and raced in a single FIM class?

eg.

1. As per this FIM document Point 2.4.3 says the following engine configurations comprise the Superbike class.
750-1000 3/4 cyl
850-1200 2 cyl

2. As per the same FIM document Point 2.5.3 says that the following engine configurations comprise the Supersport class.
400-600cc 4cyl
500-675cc 3cyl
600-750cc 2cyl

How bikes of different displacement can be in the same class? Wouldn't the bikes with higher displacement have a considerable torque advantage over the lower displacement ones?

Hope someone can clarify it more.

Its a very long & lengthy discussion; hopefully this thread doesn't turn into brand war

Anything above 750cc is technically considered superbike status & anything less than 750cc is not

Well...take this hypothetical bore stroke ratios...
1. 81 X 42
2. 61 X 55
which one do you think will have more torque?

Using displacement, cylinder count or stroke alone to decide vehicle category is IMHO a really stupid thing. I think the best way to compare 2 bikes which are otherwise identical is power/mileage ratio. In UK for example vehicles are taxed depending upon their emission. That is a smart thing to do.

Otherwise you'll have companies shouting about "fastest quarter", and short stroke bikes that revv really high would rule the world (they are just starting to infact) when the efficiency of the bike *could* be improved using higher displacements but milder tuning (like Royal Enfield UCE 350 Engine).

In a Four stroke engine there is only one power stroke for every other three strokes.In a single cylinder of 4 stroke cycle, only one power stroke is there. In a Twin cylinder engine every alternate stroke is a power stroke due to the addition of another cylinder which will fire at 180 degrees difference from each other.This is equivalent to a two stroke cycle and hence the increased traction and power...The Ninja 150R two stroker makes 30 Bhp with 120 Kgs weight.
An injected Two stroke engine is far more powerful and less polluting than a 4 stroke engine. of similar displacement and system

We have to respect the intelligence of the members sometimes.

Well, thats what the specification says, but only for 4cyl. If Ducati happens to wrap a full fairing around the 803cc Monster engine, it won't get classified as a SBK.


Well, so long as the Compression ratios are constant, #1 will have more torque because it has more displacement.
More examples: Ducati Panigale 1199 has 13.5 Kg-m Torque, BMW S1000R has 11.x Kg-m Torque. Both bikes make 195 bhp. Both bikes come under SBK classification.

@PSR sir, Could we first discuss only 4S please? We can move on to 2S later.

well, to put it very simple,

power = torque X rpm
so higher power means either higher torque or higher rpm

generally, the torque is dependent on BMEP (Brake Mean effective Pressure). in simple terms, average pressure acting on piston. and this a restriction of material used for the block and head.
another thing that the torque is dependent is the cam profile, tuning of engine. for high rpm engines, the cam and tuning is set for high rpm performance and hence torque spread is compromised.
for low rpm engines, the cam is set for optimisation at low rpms and hence the engine has a much higher torque.

now coming to no of cylinders

for multicylinder engine, due to balancing of piston movement, the rpms that can be achieved is higher (around 18000 for race spec engines) hence for same / slightly lower torque, the power that can be generated is much higher.

for lower number of cylinder, the rpm is retricted to about 10000 and hence the manufacturers tune it for torque rather than outright power figures.

hope this clears the doubt.

edit
So frankly speaking, its all about your preference. If you need a screamer, more cyl is better. But if you want a relaxed machine, singles are better

Also, for the same displacement and rpm limit, a single cylinder is anyday more powerfull and more efficient provided that the manufacturer takes the pain.

You cannot leave out power to weight ratio or drivetrain when you make torque or power comparisons.

Torque and Max Power are two different things. This is an immensely huge discussion with a lot of variables in question.

Cheers.

I was trying to compare how the number of power stroke makes a difference ,and inadvertently mentioned a two stroker...my bad ...continuing on the 4 strokes..let us compare only 4 strokers
Honda Single cylinder 250cc ...CBR 250R......25 Bhp
Ninja Twin Cylinder 250cc ......N250 R.........33 Bhp
Honda 4 Cylinder 250 cc ......Cbr 250 RR.....45 Bhp

All are DOHC 4 valves per cylinder and Fuel Injected..

As far my understanding goes, multi cylinders kind of have less stress than singles.

The reciprocating mass in the engine is divided into multiple cylinders. And handled easily in comparison. And it can be balanced by offsetting the firing order. In a sense the cylinders balance themselves. No need of extra counter rotating mass.

A four cylinder will be smoother and have better feel at high speeds than a vtwin. I think it is similar to adding more processor cores in a computer. I may be wrong. :P

One of the most informative threads on xbhp.. a goldmine for us n00b's but sadly am not getting most of the tech terms

Easily understandable....

And about the two stroke engine is also a very good topic....

Have one more question in my mind, how a parallel or V-twin cylinder differs technically...

Please enlighten me why I should include another irrelevant variable (weight of vehicle) when I want to compare just the engines when there are already so many to take care of? Also enlighten us how the drivetrain/vehicle weight affects an engine's capacity to produce up/torque. Eg. If the 250cc engine from a NINJA is bolted onto a TATA NANO (vehicle weight increased), how will the engine's torque / hp be affected ?

And that's the exact reason why we have this dedicated thread.

@Rockerz use the currently sold 150cc bikes as an example and elaborate how bore x stroke or peak power / peak torque RPM affect the actual peak torque (not peak power)

To give you a varied dataset, choose
1. Pulsar 150 (long stroke??)
2. Unicorn (Square)
3. CBR150R (short stroke)

The perfect example is CBR 250 itself

1993 CBR250RR - 4 Cyl , 45.0BHP @ 15000RPM, 21.5NM @ 12000RPM
2011 CBR250R - 1 Cyl, 26.2BHP @ 8500RPM, 22.9NM @ 7000RPM

Combustion Chamber

1993 CBR250RR - 48.5mm x 33.8mm X 4Cyl
2011 CBR250R - 76.0mm x 55.0mm X 1Cyl


Due to more cylinders the engine is capable of working at higher RPMs at ease without any stress. Heat generated by 4 X 62.2CC engines will be much lesser than 1X249CC. Hence the 1993 CBR250's sprocket combination is achieved to hit the world's highest motorcycle redline at 19,000RPM generating 45BHP power output. Thus with a Single cylinder engine the 2011 CBR250R lost the RR tag (Race Replica), also there are other aspects for CBR250R to lose the RR tag like chassis etc.

Draw backs, are the cost and efficiency. A multicylinder engine like the 1993 CBR250RR has 16Valve head and the crankshaft is supported by 4 con-rods, hence the cost involved in preparing such a complex multicylinder unit is much higher when compared to a single cylinder, same as the maintenance (viz, Servicing cost, Servicemen skillset etc). Also revving the bike at higher rpms all time to be at the power band will not help the gas mileage either.





Also the above example can be applicable for Yamaha's RD350 and RE350 as well, Over 350CC the comparison goes upto to Ducati's twins vs other Inline 4Cyls. Inshort with lesser cylinders you gain more torque at minimal engine operation (low RPM) while more cylinders makes your engine stress free making more power and hit the power-band at maximum engine operation. (High RPM).

Good one there Harish

But the point to note here is the value of peak torque in Nm. Now include the Ninja 250R and GT250R to this, all 4 vastly different engines with vastly different power outputs, but almost same torque.

Brings me back to my original query. How Panigale and S1000R can competitively race against each other in the same FIM class when the Panigale has 22Nm extra torque!! What will guarantee that it doesn't win all the time and the races remain competitive?