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hey guys can pls tell me wht exactly is tourqe and rpm? how do they increase mileage or power? how are these two inter realted?

Well I am not a big expert but I'll try ..I am sure better answers will come from others

RPM = revolutions per minute - relates to speed at which the engine (crankshaft) is spinning

Higher the revs (rpm) more the power (since the engine is running faster)

Torque - its the force which acts on the wheels to make them move
so more torque is needed to move a stopped vehicle than a moving one.

there is a formula which relates torque, power and RPM - at an rpm of 5252 , torque and power are the same (numerically)

btw you can always google for such stuff and also check out www.howstuffworks.com

Put in simple terms, Torque is the twisting force..
and rpm is the speed at ich a shaft rotates (rotations per minute)

A multiplicationof both will constitute Power..

A locomotive engine can rotate only at 600 rpm, and produce huge torque to lug such a heavy load. (a few Mega watts)

and cassete players' motor can rotate at 11000 rpm and can be stopped at a touch of a finger. (about 1 Watt)

A juice blender rotates at 18000 rpm and also capable of mincing your fingers if you try to touch. (600 watts)

let the thoughts flow..

does that mean the lesser the rpm and more torque, does engine wear out faster, and how does tourqe and rpm effect mileage

Lesser RPM is more life for engine and not the other way round. In practical sense, more low RPM torque translates to driveability in city with lesser gear shifts. High torque at high RPM means you should redline your car every now and then :-)

I won't relate RPM to engine life unless we talk about RPM variation on the same block without any improvement in technology or quality. But practically different manufacturers tune or design their engine differently to last more when their car is supposed to run at those RPMs.

You can't say that a Honda City Vtec would have a shorter engine life than a 1.5.

Torque and RPM

Guys I just coudnt find another link that explains things as well as this one...

welll if low rpm is greater engine life, then how is better mileage extracted by low torque and rpm?

No! They are independent. third example was intended to clarify that..

But for a given motor, you can equate so by manupulating the gear ratios. Thats what exactly a gear box does.

no, wht i exactly wanted to know was how better mileage is achieved by increasing or decresing rpm or torque. Is there any relaion to it|?

The answer is not simple..
The Power of the engine is fixed for a given rpm. and so is the torque.

And you have teh gas peddle to vary the speed, there by the torque.

If you look at the power anf torque curve, you may atempt to find a perticular rpm where multiple of the both figures are max. This should be the point the engine will be most efficient.

Gear boxes are designed to keep the engine revving around these speeds while delivering power to wheels.

if thats the case is there any possibility in further decreasing the rpm of my wagonr for better mileage

what do you mean decreasing rpm?? as in a governer ?
Idling rpm could be reduced but do you want to reduce rpm while driving ????
Your right foot itself is the means of decreasing your rpm....the more you press the throttl , more your rpm and more fuel you burn
so more mileage - drive in the optimum rpm band/gear and speed.

whats the difference between torque and bhp ??Me always confused with it....How are they connected???

Roughly speaking, Bhp = Torque x Speed