Hello All

I will be making a long statement to follow this post to describe how I percieve torque and it's effect on accleration, but for now I would like to make a basic statement as follows: -

The more torque available will allow a car to accelerate fatser as toque defines how much power is tranmitted to the ground to propel a car forwards.

basically stating torque is the most important thing to refer to when it comes to ability to accelerate!!

Ok any responses to this vague (for now) question will be greatfully recieved

Q

Torque will tell you how much power you have available at the exact point in time when you press the pedal. Power is a more useful figure as it effectively tells you how much torque you have over the whole rev range.

However, a car with a high torque figure may be more fun to drive than a car with a high horsepower figure, as the power comes in a big 'lump'.

So, in answer to your question, the car that will accelerate fastest is the one which has the most power, so long as you use the whole rev range. If you are looking to accelerate only briefly (without changing gear), then torque is more important.

Please, correct me if I'm wrong; I know this is a contentious issue, and I've just got in from a pub crawl, so prob ain't the most sober.

Hope that helps,

Rob

Totally disagree with the concept that the bhp figure tells you how much torque you have over the rev range unfortunately though

A high-revving petrol with say 200bhp vs a slow-revving derv with 200bhp will have a totally different torque (and for that matter, power) curve.

Torque at the wheels determine acceleration ability. Power is needed to push the car against the wind and other forces that apply to the car when moving it about generally.

(turbo)diesels tend to have a fairly large torque spike low down the rev range whereas most petrols don't do anything below 3000 rpm really.

The gearing is really important though, as petrols have a more usable rev range they tend to be able to stay in the same gear for longer.

It's fun to rid the torque wave though admittedly, but if you take a (randomly picked) car like Des' Octy and the turbo kicks in hard higher up the rev range, you'll enjoy a VERY nice push into the seats

I'd just enjoy the car regardless though

but des's car is standard?

I know It IS a 1.4 IIRC :D

The more torque available will allow a car to accelerate fatser as toque defines how much power is tranmitted[/b'] to the ground to propel a car forwards.

Good christ man, if you want to be known as a 'Q', then correct your spelling

Q.

doesn't it also depend on what speed you want to accelerate from - harping on about the old upper heyford videos, wouldn't a one click'd fabia vrs have more torque than a jabba'd 1.8T octavia? the fabia got whooped in each of those videos - don't think it's as simple as looking at a car's torque figure :confused:

Totally disagree with the concept that the bhp figure tells you how much torque you have over the rev range unfortunately though

Aye, reading that now, **** knows where I pulled that from!

(in response to andypandypoos)

It isnt

If both cars are in the most appropriate gear, the torque at the wheels is the starting point. If say the torque of the TD was higher at that point, it would (assuming same weight, which isn't the case either) drive away from the petrol car. However, as the diesel car would have to change up a gear more quickly it would stop accelerating during the gear change, and in the higher gear less torque would be at the wheels (as the gearbox is a torque converter effectively). During this time the petrol car would take off.

That's also why at a 0-60 more than likely the petrol car would 'win'.

From a standing start therefore a diesel would struggle a LOT. There are some that are quicker than others, but still

Rolling start it should be closer but only within a certain (small) speed range. Top speed wise, most petrols are geared such that they'd drive off again

(and yes I drive a diesel )

Good christ man, if you want to be known as a 'Q', then correct your spelling

Q.

It was 3 or 4 in the morning and I just came in from a 12 hour work day, normally I proof read before submitting, but was to tired too....

Also I shorten my name to Q from Quetzalcoatl a Mayan Demi god, some theories would suggest a person from the city of 'ATLANTIS' he is supposed to have been a person who was going around 'Civilising' humans. Supposed to have 'Magical' powers and all, not to unsimiliar to that of Jesus and other mythalogical characters that exsisted throught time. Which could get me on my boring oppinion that They were all the same person.... and this individual was either a Alien or just like in Stargate an 'Ancient' the first evolution of this form

As it say in my signature 'Insanity is not an illness, it's a way of life'

Q

ok the second install ment of my question

My understanding is a diesel will initally accelerate faster then a petrol equivilant but as the torque will peak out at a general rule of thumb around 2,000rpm - 2,200rpm that will force a driver to change up earlier due to the torque dropping off at that point, though you can continue to accelerate upto 3,500 per say before it come quite pointless to stay in that gear due to the drop in torque.

But a petrol like a Vectra 1.8 like my mates has something like 125lbs/ft @ 5,400rpm, he will benefit from the pull from his torque band upto 5,400 and possibly still pull upto 6,000rpm, allowing him to stay in that gear far longer then a diesel would. However due to lower available torque at lower engine speed will propell him slower then the diesel would at that lower rev range.

What I am trying to say there is diesel accelerate faster then a petrol, because a diesel has approx 80% more torque available then a petrol with similiar BHP's, but due to the fact the petrol can go to 5,400rpm before it runs out of torque 'Pulling Power' and therefore can ultimately out accelerate a diesel as he will require changing up sooner due to the torque dropping of erlier then the petrol equivilant.

On that basis to make a diesel car better at accelerating and improving overall 0-60 time the trick would be to do what Toyota has done with the Yaris 1.4D-4D 89bhp car. As the torque Peaks at 2,000rpm and stays at I think at 140lbs/ft until 3,000rpm, which how I understand it will allow this car to accelerate far better due to the torque going to 3,000rpm and that is a reason it will go 0-60 in 10.5secs where my 1.4TDi furby with only 14bhp less but 4lbs/ft more torque will go 0-60 in 14secs due to the torque peaking out at 2,200rpm.

Ok there are other considerations to take into account, Like gear ratio's (Another important thing to look at) Mass of car, wind co-efficent and the list goes on.... but my statement of the more torque available the more 'Power' available at drive wheels!! is correct.

Therefore improving the amount of torque available and at a higher rev band will make sense. Or will it just be better to make a diesel revs upto 6,000rpm and that torque has little to no effect in the cars acceleration and is only there to provide the ability to lugg big weights around and has No effect to the acceleration capability like my mate seems to believe !!

I look forwards to hearing what you guys think about this

Quetzalcoatl

PS Sorry for any spelling errors, I just have no energy at the moment :(

Remapped diesels pull through to the redline (or beyond if you're brave enough).

Petrols benefit greatly from raising the rev limiter (plenty of extra power that way).

Both petrols and diesels benefit from increased torque & power, more torque across rev range means easier to drive and 'smooth', more peaked power is more 'fun' I suppose

Your statement about more torque then more at wheels is correct in principle

The 2.0 PD revs up to 6000 rpm (when mapped)and that is a NICE useable extra 1000 rpm

Back to basics..........Power is "work done per unit time", e.g. 1 W (proper units:thumbup: ) is a 1N force, pushed over 1m, in 1 second. Torque is essentially a rotational force, measured in Nm, e.g. 1N (about 100g) applied to a 1m long bar. Angular velocity is "how fast are the wheels going round?", measured in radians per second. So power is total energy delivered, and torque is turning force. Combine all this, and you get:-

Power = angular velocity X Torque

e.g. if 2 cars with the same size wheels are travelling at the same speed, then the angular velocity is the same. If one has more torque, then it has more power, at that speed.

Power is directly related to torque. The difference between diesel and petrol, obviously, is that all of the torque comes lower down with diesels, and higher up the rev range with petrols (typically). An engine with relatively low torque can have massive power outputs, if it spins fast enough (motorbike engines etc).

Power and torque from an engine are converted to usable outputs by the gear box, as mentioned above, and diesels are typically slower, as you need to change gear more. An ideal situation is a drivetrain that allows the engine to run at a constant speed, at its peak POWER output (not torque), and adjust the transmission to suit the vehicle speed, thus always delivering maximum energy to the wheels, regardless of speed. This is where Audi's Varitronic, or whatever its called comes in to play, and has the potential to close the gap between petrol and diesel performance. I haven't driven one, but am told its pretty damn impresive.

Phil

Here's one for ya kiddies:-

The Emperor wants to control outer space, Yoda wants to explore inner space. That's the fundamental difference between the good & bad sides of the force.

Go figure.

Back to basics..........Power is "work done per unit time", e.g. 1 W (proper units:thumbup: ) is a 1N force, pushed over 1m, in 1 second. Torque is essentially a rotational force, measured in Nm, e.g. 1N (about 100g) applied to a 1m long bar. Angular velocity is "how fast are the wheels going round?", measured in radians per second. So power is total energy delivered, and torque is turning force. Combine all this, and you get:-

Power = angular velocity X Torque

e.g. if 2 cars with the same size wheels are travelling at the same speed, then the angular velocity is the same. If one has more torque, then it has more power, at that speed.

Power is directly related to torque. The difference between diesel and petrol, obviously, is that all of the torque comes lower down with diesels, and higher up the rev range with petrols (typically). An engine with relatively low torque can have massive power outputs, if it spins fast enough (motorbike engines etc).

Power and torque from an engine are converted to usable outputs by the gear box, as mentioned above, and diesels are typically slower, as you need to change gear more. An ideal situation is a drivetrain that allows the engine to run at a constant speed, at its peak POWER output (not torque), and adjust the transmission to suit the vehicle speed, thus always delivering maximum energy to the wheels, regardless of speed. This is where Audi's Varitronic, or whatever its called comes in to play, and has the potential to close the gap between petrol and diesel performance. I haven't driven one, but am told its pretty damn impresive.

Phil

Ok I understand what you are saying here, however correct me if I am wrong here, but when they calculate the torque outputs they are refering to the torque at the flywheel/ Final Drive or what ever it is called

And then the Gearbox acts as a torque converter depending on size of Final Drive Wheel and Selected gear. Then the torque amount is then tranmitted to the drive wheels and depending on the size of the wheels will then dictate what gets transmitted to the ground.... please correct me if I am wrong, the whole reason of this post is to see if i understand things correctly

Q (Dan)

Theres no such thing as Good and Bad forces, It's Strong, Weak, Gravity or Electromagentic, if your getting technical!

Bit off topic though!

Phil

Theres no such thing as Good and Bad forces, It's Strong, Weak, Gravity or Electromagentic, if your getting technical!

Bit off topic though!

Phil

Tell that to Darth Vader! He'll have ya arm off!

Ok I understand what you are saying here, however correct me if I am wrong here, but when they calculate the torque outputs they are refering to the torque at the flywheel/ Final Drive or what ever it is called

And then the Gearbox acts as a torque converter depending on size of Final Drive Wheel and Selected gear. Then the torque amount is then tranmitted to the drive wheels and depending on the size of the wheels will then dictate what gets transmitted to the ground.... please correct me if I am wrong, the whole reason of this post is to see if i understand things correctly

Q (Dan)

You are pretty much there. Power can be conterted between torque and speed, by the gearbox. The more you change the things though, the more you loose to friction, heat, noise in the box though. Thats partly why 4x4's are less efficient.

Also most European cars are quoted at the fly wheel.

Phil

...but my statement of the more torque available the more 'Power' available at drive wheels!! is correct...

still don't think it's that simple though, if you make exactly double the torque at exactly half the revs, everything else being equal, don't you make exactly the same power

i'm on about peak numbers, and i've read somewhere that it's not about peak numbers, it's about the area under the graph

Yep, Half the speed, but double the torque is the same power. But stats are one thing, and "feel" is another. Some like the brutal kick of certain engines, whilst other prefer the understated and refined urgency of others. Personal preference is what its all down to.

People argue statistics (0-60, 30-70 etc) but its all down to how you drive. Remember that "peak" is only at one particular point on the engine's output. In general driving, you spend very little time at peak power or peak torque (think about it as you briefly pass a particular rev number). A nice flat but wide torque band will give a steadily increasing power curve, and a more driveable engine than a peaky torque and a narrow "kick in the ***" delivery that means you need to change gear every 1000 rpm.

I like the drive of diesels over your standard 1.8 -2.2 petrol, as I like the torque, but there is no replacement for a bigV petrol. A good combination of torque and rev range ( thus power!). I'd trade most modern turbo petrols in for my little VR6, any day. Plus, the sound of a VR6 at 5000 rpm is just fantastic!

Phil

(Deep down Petrol monkey!)

(also a bit ****ed, so please take with pinch of salt - will edit when sober!)

It is about leverage essentially.

Power is a notional figure that is basically the torque multiplied by the rpm (specifically BHP = Torque lb/ft x RPM / 5252). So given two cars, one petrol and one diesel, the petrol producing 140lb/ft at 6000rpm and the diesel producing 280lb/ft at 3000rpm, if both cars are doing say 50mph at 6000 and 3000rpm respectively and both drivers floor it, the cars will (all weights and wind resistance being equal) accelerate at the same rate in theory.

The differences come in the way each engine delivers its push. Area under the torque curve is often used to get a better idea of how an engine will feel. Say the above petrol engine peak torque is a flattish line at 140lb/ft from 3000 to 6000 rpm and the diesel a big peak of say 280lb/ft at 2500rpm dropping to maybe 210lb/ft at 4000rpm. Say the petrol has peak power at 6000 rpm, it will be producing 160bhp. Say the diesel has peak power at 4000rpm it will also produce 160bhp.

The difference in the way they pull will be thus (assuming all else is contant and the gearing keeps the speeds matched):

Given petrol at 6000rpm and diesel at 4000rpm, both will pull the same.

Given petrol at 3000rpm and diesel at 2000rpm, the diesel will pull stronger as its big midrange hump of torque gives it an advantage. As the two engines head toward peak power, the diesel accelleration will fall off and the petrol remain constant, so by 6000 and 4000 rpm, both are back to equal. This is because the shape of the torque curve of the diesel will have more area under the curve between the two engine speeds.

Now take the example of the same two engines, but the petrol revs to 7000rpm before its torque drops off completely. The diesel torque is fading fast by 4000rpm. Here, the pertol engine will move into advantage as it will sustain more acceleration higher up the rev range.

So given identical peak power and typical mapped PD turbodiesel and N/A petrol torque characteristics, the diesel will generally be a little faster than the petrol bhp / bhp.

Now for the but: In the real world, the diesel has to run tall gearing to achieve decent top speed. On the other hand the engine speed range is limited so each gear covers less change of speed. The Fabia vRS for example runs 16mph / 1000rpm in 3rd, giving us a roll on from 48mph at 3000rpm. So if you run up to 4000rpm, peak power, then change up, you will be going up a gear at 64mph. You will then drop back to around 3000rpm and run up 4th to 87mph.

The typical petrol car will be in third at 4000rpm at 50mph. The roll on to 6000rpm will take the car from 50 to 90mph without a pause for gearchange. If the petrol driver was in a real hurry, he could use 2nd from 50 to 60mph then change up. If the petrol driver was on a fast sweeping curve, he can keep power on consistently so not upsetting the car, the diesel driver will have had to go into the corner a gear too high to avoid upsetting the car with a mid corner change.

Given all this, and taking two cars that have the same power and weight, but one turbo diesel and one petrol, they will cover ground at broadly similar pace. The differences will be how each suits various situations. Both have their merits, not least diesel fuel economy and the "big car" feel of the midrange, but extending a crisp N/A petrol engine out to the redline feels good too.

Chris

I think another comparison on "feel" might be like this:

A "small" TD "feels" like an American "small-block" engine (5.7litre V-8). I used to drive one years back. Only 350 bhp but tons of torque. Lots of fun spinning the rear 18 inch wheels. The same 5.7 litre petrol engine could only rev to about 5.5K. As a mag at the time said : " all you get beyond 6K is noise...".

Perhaps that's why I like my derv so much....