what is PSI? and tourers need more torque than power and rippers need more power than torque??? right or wrong???? and plzzz tell me what psi stands for!!!

^^ PSI is the imperial unit of measuring air pressure. It stands for pound per square inch.

so this has nothin to do with power or torque???

PSI = Pounds per Square Inch

In metric system it is KG per Square CM. Units to measure pressure.

To my understanding you are correct about your torque statement.

thank u for giving me the explanation about psi!! but where is ths pressure used??? what applies pressure on what??? and what happens due to this pressure????

Pressure is a force on a limited area. Air pressure inside the tyre will keep it inflated. Pressure on the piston will force it downwards and rotate the crank. Pressure in the brake lines will stop your bike. So there you have it, the uses of pressure.

In case of an engine, it gives us a measure of the compression ratio of the engine. Also a good engine will show higher cylinder head pressure compared to one with worn out oil rings etc.

ok so this pressure is the pressure applied by the piston to compress the air fuel mixture????

Yes. This happens during the compression phase. The combustion phase is the opposite and is not generally measurable without special equipments.

Pressure, as abhijeet says, is a force applied on a certain area. Thats still somewhat bookish eh! All right....lets take an example of air pressure. Air pressure is the result of cramming air into a certain space. Cram air inside somewhere i.e. more air than is usually 'normally' present around us (thats air at 'atmospheric pressure) and it tries to escape, meaning it exerts a 'force' on the walls of the container in an attempt to escape from it. The more air you cram in, the higher is this 'force' or 'pressure' that it exerts in trying to escape into the atmosphere. To increase your bike's 'tyre pressure' for example, you fill it with more air. More air into the same amount of space (or volume as three-dimensional space is called) pushes harder from the inside of the tyre and at the inside of the rim i.e. it tries to escape with more 'force i.e it exerts more force per unit area on the inside of the tyre. And in resisting this 'attempt' of air to escape, the tyre becomes stiff. Allow this air to escape through a puncture (i.e. reduce the amount of air inside the tyre) and the pressure 'drops' inside the it and the tyre goes limp. As a proof of this need for 'more' air to increase pressure, try inflating your bike tyre and an SUV's tyre with a foot pump. While the bike tyre will inflate to say 25 psi with some 50-60 strokes of the pump, you'll need to pump away for some 4-500 odd strokes to get the same 'pressure' reading for the SUV tyre.

The same 'physical' understanding can be extended to any 'pressure'. The piston travels from the Bottom Dead Center (BDC) to the Top Dead Center (TDC) during the compression stroke. In doing this it effectively reduces the volume available to the air inside the cylinder. Reduce volume or increase the quantity of air in the same volume...the effect is the same....which is to increase 'pressure'. So we say that the air has been compressed. When fuel gets burnt in this compressed air, the rise in temperature further increases the pressure and so forces the piston downwards, making it rotate the crank and you get the power stroke.

^ Thanks for helping me out there!

knn filters do what???? increase the supply of air to the carb right???? but then the fuel will get reduced and the air will increase right????

throttle means acclerator right????

how does the cubic capacity affect the power out put of the engine????? i hjave seen the r 125 only 125 cc but can lierally take over the p180 for sure!!! and same with the r15!! can beat the karizma even if its 150 cc

cubic capacity

how does cubic capacity make a difference in biking experience??

Yes, to compensate for the increased oxygen flow, we often change the "Main Jet" of the carburettor, to a bigger one.
Main jet is a small cylindrical metal component with a circular hole in the middle for sucking up fuel into carb. I have seen it myself.

Replacing the main jet with a bigger one is also called "rejetting". Browse Xbhp for more details.

Yes. Precisely, Accelerator is on your right hand. Throttle is inside the machine, but these 2 things are linked and are used synonymously often.

Technology is a small influencing factor here, but the major reason for this, is "Tuning":-->

R125/ R15 have been tuned, to make more power at high rpm's. But, it won't be too much at lower rpm's.
Most of our Indian-made machines (P180, Karizma, etc.) have more torque/power at lower rpm's than these bikes.

Google "Torque vs Power" and read many such articles on net about it. Basically, Torque & Power are same things, but with a factor to separate them: RPM/ Engine Speed.
Power = Torque x RPM is the formula.

So, a bike revving upto 16,000 rpm will give lots of power. But, a bike with rev ceiling at around 5000 rpm will be less powerful, but torque would be quickly accessible.

Another example, Karizma gives 17 bhp power @ 7000 rpm. P220 gives 21 bhp @ 8500 rpm.

And so, karizma engine has lots of torque at lower rpm's making it ideal tourer. And P220's ideal for drag races, where it beats the ZMA hands down...

Generally, More Power results in Quick Acceleration & more Top Speed in straight line & high throttle..

So, More Torque-based Tuning helps in pulling weight easily, and giving desired response at low rpms. Ideal for Commuters. Also, Torquey machines are good at mileage too, than high revvers.

An Indian Train engine, say has lots of torque, but it can hardly accelerate, or go beyond 130-140 kmph either, despite a big engine.

"Generally" speaking, More CC would mean more torque, power and lesser mileage (Again "generally", as mileage is a factor of various elements)

I strongly suggest that you SEARCH & read Xbhp's articles and posts for already printed knowledge.
Believe me, almost everything you asked is already posted somewhere or the other place. You'll have to search though.