Power vs. Torque

workaccount

Hi,
If you have a 2.0 diesel with loads of torque and a 2.0L petrol with more power.

Let's say both cars are the same weight. What good is the extra torque then in the diesel?

Is the only time you need the extra torque if your pulling weight or does that torque come in handy if your pulling out of corners aswell?

Gumbo

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

Victor_M

This topic has been covered plenty of times on boards.ie, do a search and you will find all you need to know about BHP vs Torque.

E92

+1.

Anyone who thinks that diesel is "way faster" than a petrol of similar bhp clearly can't/won't drive a petrol properly.

Diesel is great...until about 3500 rpm and then it loses the will to live, and also if you have a phobia of changing gears(and if you do then it's time you got an Automatic or stopped driving). Petrol may not do a lot below 3000 rpm, but give them a few revs, bring them up to 4, 5 or better still 6,000 rpm and it's a whole other world.

unkel

E92 wrote: »

Anyone who thinks that diesel is "way faster" than a petrol of similar bhp clearly can't/won't drive a petrol properly.

That's pretty much it. Look up the 0-100km/h of the petrol vs the diesel and the petrol is always quicker. The vast majority of people rarely if ever drive like it is a 0-100km/h contest though. The plentiful torque at low revs makes them think (wrongly) that the diesel is the more powerful car

There are however situations in real life where the diesel will be quicker, i.e. in a situation like overtaking where you can stay in gear in the diesel and you lose time in the petrol because you have to down-shift

Biro

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.

Notch000

perhaps revelant ?
http://www.justgofaster.com/Articles/CarStuff/DeiselvsPetrol/tabid/177/Default.aspx

Soarer

Notch000 wrote: »

perhaps revelant ?
http://www.justgofaster.com/Articles/CarStuff/DeiselvsPetrol/tabid/177/Default.aspx

That's that then.
Petrol's for hooligans, and diesel's for sensible people in brógs.

conneem-TT

Here's a good read about horsepower and torque.

http://www.vettenet.org/torquehp.html

Gumbo

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.

LOL yeah you prob would mate!
im not saying the civic is slow or my comparision is the bible, just my 2c.

Anan1

Torque is king in cars without gearboxes.

Sandwich

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?

VH

Anan1 wrote: »

Torque is king in cars without gearboxes.

ROFL!

E92

Anan1 wrote: »

Torque is king in cars without gearboxes.

+1. Which is why petrol is better(and faster).

Steve

Sandwich wrote: »

Anyone remember when power/weight ration was king?

What's this remember stuff - it still is.:D


Good post.

TheDriver

Diesel seems better bet if your going around corners and up and down hills etc, country driving as saves changing gears as much, city driving would probably prefer petrols I would think.

conneem-TT

stevec wrote: »

What's this remember stuff - it still is.:D


Good post.

It's seem like g CO2/km is more important now :mad:

craichoe

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

Be not afraid

https://www.boards.ie/discussion/comment/55933824#Comment_55933824

If the rule is the car must be kept below 4000 rpm, the diesel will win every time. What RPM do people normally drive their cars 99% of the time? < 4000 rpm. So at 2000 rpm a petrol may only put out 30 hp but a diesel puts out 50 hp. So 99% of the time the diesel is more powerful and 1% of the time the petrol is more power when it's strung up like a yamaha motorcycle to 6500 rpm. so only peak hp is higher is a petrol car. If you drive at peak hp all the time to beat your diesel brethren, your engine may not last a month and you'll be tired of changing gears (and diapers) at every incline and you'll be depressed by your noisy weak car that only performs when the engine makes a scene.

bazz26

Wow, 15 years later.