Power vs. Torque

kceire wrote: »

i have a 116 bhp D4D avensis (2.0 TD)
my GF has a 110bhp civic (1.6)

and mine is a faster car.

so i guess the old saying is true : BHP sells cars, torque wins races

I'll put money on it that if you give me your girlfriends civic, I'll beat you in your Avensis. Straight race, standing start to an agreed cut off speed.

Grossly simplified (engineers, please avoid correcting the techniocal smudging), but :

Torque is force by a distance - in a hand waving way : the idea is how strongly a shaft would resist a force trying to stop it.
Quoted torque for cars is at the engine output.
What moves a car is torque at the wheels drive shaft, ie after the gearbox.
Gearbox ratios are designed to suit the speed/torque curve of the engine.
More torque has no benefit if it does not translate to more torque at the wheels.
More power does mean a car( all else being equal) can go faster (eventually!) - more torque doesnt.

Traditionally, high torque was prized by those pulling loads, as you mention.
Which was a shorthand for prizing high (engine)torque at low revs. i.e. you did not have to rev hard, feel that your were really pushing the engine to get good torque at the wheels - and move your heavy load.

In recent years, with the rise of the turbo diesel and its characteristic of high torque at low revs compared to similarly (or lesser) powered petrol cars, a 'high torque, pulls faster', 'its torque that matters' etc idea has spread.

Due to :
Torque in turbo diesels tends to be high much lower (eg3000rpm) in the rev range than petrols (eg . 5500rpm).
At trypical driving speeds and gearing, the diesel engine is closer to its peak torque range than a petrol. When accelerating, to get the same torque to the wheels, the petorl driver would have to change down a gear or two (and raise the revs to get the same wheel speed). Giving the high torque engine driver the impression that his car has more go. But really that is because he didnt have to change down (saving him the effort) and the engine pitch is not rising as much as he accelerates(giving him the impression that the engine is accelerates the car more easily).
(Non turbo) petrol cars generally rev faster and more smoothly at lower speed than turbo diesels (which are the phenomenon that has given rise to the average motorists understanding of bhp not being the whole story and maybe torque figures are worth a look). If you compare 0-100 times for general equivalents in most cars, (say Passat Tdi140, and Passat 2.0petrol 150) they are (roughly) similar. But as well as the reason above(engine rpm), people will say they find the high torque a more responsive car. And in fact it is - in the speed range that they use to form their opinion: overtaking, from 70kph to 120kph. The petrol engine having got from 0-30 faster than the higher torque engine is not really noticed - it happens in a less 'practical', 'useable' range. So again the impression that the higher torque version is 'faster' is conveyed.

Sum:
For real world driving - higher torque gives a little bit of genuine driveability conveniece, and to a greater extent an impression of being faster(colloquial for 'greater acceleration').
It depends how you drive it and in what situation you are looking for its best performance.
Increase the revs of the lower torque but similarly powered engine and you will get similiar performance to the higher torque engine.
Rev your petrol car and it will accelerate as quickly (if not more quickly) as the higher torque version.
Anyone remember when power/weight ratio was king?

Biro wrote: »

I'll put money on it that if you give me your girlfriends civic, I'll beat you in your Avensis. Straight race, standing start to an agreed cut off speed.

Course you could, rev the bollocks off any petrol and you'll get decent power. Although, put four americans in each car and now see who would win a race :P