few elementary questions

[Most Wanted]

Hi there,

i'm new to the world of cars, and have been reading fast and furious different types of articles, how to's, etc in order to learn how this all works.

horsepower vs torque
i know torque is a force that turns an object and is force times lenghth, while hp is power output of the engine, but my question is, aren't these the same thing, they both measure engine power? i guess what i'm trying to ask is what is the difference when a brochure says 340 hp and 290 torque.

and then along those lines, what does it mean to achieve top hp or top torque at low rpm vs high rpm, which is more preferable? i know tractors use low rpms to get top hps in order to conserve the engines for thousands and thousands of miles, why can't a car use the same low rpms?

cheers

 

[HDi fun]

Torque is a measure of force. BHP is a measure of how quickly work is conducted and therefore necessarily includes a time element. So power = torque x revs per unit of time. Forget specific units, it's the principle we're interested in.

Simplest analogy is that a reciprocating steam engine produces maximum torque at ZERO rpm. But therein lies a paradox. How does it get the train moving if its producing no power?

 

[obi_waynne]

Both are measures of the same thing - engine power. One takes into account engine speed as HDI says.

Torque is a better indicator of how much shove a car has. The more torque you have and the wider this is spread over the RPM band the better.

A turbo diesel car does use low RPM power.