From whatever little I know, I chose HP. I think its a bit like asking to choose between an elephant (torque=pulling power) & a horse (HP=Speed). I think torque becomes important in ghat scenario or off-roading purposes. For normal city riding/driving power is more important, isnt it?

Also, at the start of the thread someone mentioned about lesser cc=less stressed engine. Can somebody explain how (in simple terms). I always thought more cc=less stressed engine. That having less cc & producing more power will stress the engine, like MotoGP & F1 machines. Reliability will be an issue.

My technical knowledge is rather limited and would be happy to add to it, preferably minus the formulae

less cc can be used to produce more power by making it rev higher.

your 150 cc bikes can produce heaps more power if they make it rev higher but it would considerably reduce engine life.

more bhp

i would prefer more horse power...
like R15 churns out 17bhp with only 150cc engine
whereas 225cc Karizma develops nearly the same power with 225cc ...

Personally speaking.....


Torque is the criteria which makes a bike more fun to ride wid superb feeling.....

Stressing of an engine has nothing to do with cc. Confirmed!

You know Kawasaki has manufactured a Ship engine, 4 Floors tall, making thousands of horsepower @ just 90 rpm! and it is not stressed at all, despite the size.

It is all about tuning. and mostly the resulting rpm (engine speed).

In modern engines, Piston Speed should be minimum possible. It is in straight connection with Stroke Size & Rpm.

In simple words, you can remember that High revving engines would result in more friction. That's it ...


and yes, torque & power are quite related to each other, ok?

Well, the karizma is not the best example of a long-stroke torque monster and its not a lazy revver either. I have a 12000rpm revving karizma example with me and its as rev hungry as a square engine, if not over-square.
The karizma at 66.2mm stroke is by no means a ballistic stroke length when compared to a 90mm stroke of a bullet. Now thats quite a long travel, not this.

About the high revving engines, well now that does not mean engine life is gonna be any shorter than a long stroker.
A short stroke engine has lesser piston speeds and hence the wear and tear if compared on a proper scale is equivalent to a long stroke engine for x number of kms.
For ex, an Apache 150 which revs max till about 10500rpm might have a cylinder life of 60,000kms. Now an RTR which revs till 12000rpm and makes more power still will give the same engine life, courtesy lesser piston speed and a few other factors.
The R15 is a square engine, but it has ultra light internals to compensate and rev like a short stroke engine. So matters vary from case to case,.
In the end, all the engine dynamics are in the hand of the maker. They can make it last or break despite having absurd bore/strokes.

@Joel : Can u throw some light on swirl induction/ATFT whatever?

I have observed that engines which sport this type of air induction are mcuh smoother. Any reasons?

IMO, they generate turbulence in the incoming mixture such that air and fuel gets mixed properly. Turbulence also helps the fuel to atomize further. And, finally more mixture can enter the combustion chamber due to the increased mixture velocity.

Ultimately, engine efficiency improves, especially at lower rpms, where the mixture may have a tendency to come out through the inlet port before the valve closes. So, lesser vibrations.

Feel free to correct me if I am wrong.

That s a pretty good explanation bro!

And these are not high-performance engines. Its explained well above by abhijeet.
Its to basically help improve combustion efficiency at lower revs.
In a high performance engine, with a high velocity port and demanding rpms, there is no time for swirl.

But as far as I know... suzuki swift also use this tech of swirl induction and yet it is one of the cars with bad low end torque......

Look at the bore/stroke of the swift engine. Its almost a square engine and the ports are large for high-end power.
If you compare the low-end torque of the same G13B engine in the esteem, this is pretty commendable. Maruti has worked on the intake tract and boosted the low-end to a decent extent.

couldidnt have said it better!..my explination was a bit of a generilization

agreed the karzma does rev too...but comparing the karzma to some of the current bikes.lets say the r15,rtr..it aint much of a screamer..but sure is the most torquee..

R15 is only 150cc. But it can smoke zma(225 cc) and p220.
I feel cc can be substituted with technology.

Yeah, upto a certain extent!