lets talk about torque

[Suprasteve]

its a hard one to explain, would you agree with the following comment i read somewhere ?

 

"Torque will give you better lower speed accel, drivability, and throttle response while high hp will give you better higher speed or high speed accel. f1 cars have barely any torque but some 800hp because they are so light they don’t need the torque to move their small weight."

 

I know theres many other factors to take into consideration but does anyone else have a lamens term of explaining it ?

 

I can do a Google search and read many links but seeing as this is a forum i thought we could do this the old fashion way and actually discuss the topic....

[spidermonkey]

torque is basically a twisting 'moment'

[b_have]

Torque X rpm = horsepower. So, an F1 engine reving to > 19000 rpm produces a lot less torque than a Supra

[SimonB]

Torque is the thing that accelerates your car, it's the force that pushes it forwards effectively. The thing that's important is the torque at the WHEELS though. This is why people banging on about how much torque their diesel has and therefore how nippy it is are not really right. If the engine revs much lower then you have to use a higher gear ratio to get the same top speed - therefore less torque reaches the wheels. An F1 car revs very high, so you can use lower gear ratios and more of the relatively low torque reaches the wheels - nothing to do with weight.

 

E.g. say you have 2 engines, 1 revs to 10000rpm and produces 200ft/lbs torque. The other revs to 5000rpm and produces 350ft/lbs. On the face of it it looks like the 2nd one is the one to have. But you want them to go the same speed, so if no.1 has a 1:1 gear ratio say. No.2 will have to have a 2:1 ratio to go the same speed. So no.1 has 200ft/lbs of torque to the wheels whereas no.2 only has 175ft/lbs.

[Cable]

Torque is the thing that accelerates your car, it's the force that pushes it forwards effectively. The thing that's important is the torque at the WHEELS though. This is why people banging on about how much torque their diesel has and therefore how nippy it is are not really right. If the engine revs much lower then you have to use a higher gear ratio to get the same top speed - therefore less torque reaches the wheels. An F1 car revs very high, so you can use lower gear ratios and more of the relatively low torque reaches the wheels - nothing to do with weight.

 

E.g. say you have 2 engines, 1 revs to 10000rpm and produces 200ft/lbs torque. The other revs to 5000rpm and produces 350ft/lbs. On the face of it it looks like the 2nd one is the one to have. But you want them to go the same speed, so if no.1 has a 1:1 gear ratio say. No.2 will have to have a 2:1 ratio to go the same speed. So no.1 has 200ft/lbs of torque to the wheels whereas no.2 only has 175ft/lbs.

 

 

 

Makes sense to me

[Gazboy]

The old F1 cars with V10's made 350lbs.ft of torque.

 

Torque= work

Power= rate of work.

[Snooze]

Torque is the thing that accelerates your car, it's the force that pushes it forwards effectively.

 

I was with you up to that bit, then it all got a bit hazy.

[Suprasteve]

Torque is the thing that accelerates your car, it's the force that pushes it forwards effectively. The thing that's important is the torque at the WHEELS though. This is why people banging on about how much torque their diesel has and therefore how nippy it is are not really right. If the engine revs much lower then you have to use a higher gear ratio to get the same top speed - therefore less torque reaches the wheels. An F1 car revs very high, so you can use lower gear ratios and more of the relatively low torque reaches the wheels - nothing to do with weight.

 

E.g. say you have 2 engines, 1 revs to 10000rpm and produces 200ft/lbs torque. The other revs to 5000rpm and produces 350ft/lbs. On the face of it it looks like the 2nd one is the one to have. But you want them to go the same speed, so if no.1 has a 1:1 gear ratio say. No.2 will have to have a 2:1 ratio to go the same speed. So no.1 has 200ft/lbs of torque to the wheels whereas no.2 only has 175ft/lbs.

 

ok i think i follow what you're saying.

 

what engine would you have in the supra (i.e. assuming its the same car, same weight, same gear box and revs to the same max rpm)....

 

A) 400bhp & 400ft/ lbs torque

 

B) 300bhp & 500ft/ lbs torque

 

C) 500bhp & 300ft/ lbs torque

 

or would there be pros and cons for each of them ?

[Gazboy]

ok i think i follow what you're saying.

 

what engine would you have in the supra (i.e. assuming its the same car, same weight, same gear box and revs to the same max rpm)....

 

A) 400bhp & 400ft/ lbs torque

BPU 2JZ

 

B) 300bhp & 500ft/ lbs torque

That V10 TDi Toureg off roader engine.

 

C) 500bhp & 300ft/ lbs torque

M5's V10

 

or would there be pros and cons for each of them ?

 

..

[SimonB]

ok i think i follow what you're saying.

 

what engine would you have in the supra (i.e. assuming its the same car, same weight, same gear box and revs to the same max rpm)....

 

A) 400bhp & 400ft/ lbs torque

 

B) 300bhp & 500ft/ lbs torque

 

C) 500bhp & 300ft/ lbs torque

 

or would there be pros and cons for each of them ?

 

You probably wouldn't get those figures in cars with the same gearing. Power is derived from torque. As b'have posted up, power is torque x speed (in this case rpm). If you had 400ft/lbs of torque across the board at all rpms then power would rise with revs. The values you see stated are the maximums, wherever that is (normally you see something like Xft/lbs at Yrpm). For you to get those figures B would have to have low down torque that drops off at higher revs, and C would have to have not much torque low down and that 300ft/lbs at higher revs. Which is best depends on when the torque peak is, and what the torque curve looks like.

[dangerous brain]

Ideally you want hods of torque from as low an engine speed as possible all the way to the engine limit, with a nice high limit of above 7k rpm. Not many cars manage this. From what I remember from an old series of top gear though they managed to put the sporty 5 series beemer diesel around their track quicker than they could get the same year M5 around it.

[Daston]

This is why V8's make a good engine. They have lowish rev's but have a high tourque through out their rev range.

 

2 examples

 

1) My 2JZ-GTE puts out roughly (not yet been on dyno) 360bhp and 350ish ft/ibs of tourque

2) My old mans Rover V8 puts out 300bhp and 290-300ish ft/ibs of tourque.

 

After driving both cars his is a lot easier to drive quickly as the tourque is accessible in pretty much any gear nearly through out the whole rev range so over taking is just a case of planting it and pulling out. Where as the supra only has the max tourque higher up the rev range so you need to be sure your in the correct gear and revs before nailing it.

 

Well thats my take on things not very technical.

[Suprasteve]

From what I remember from an old series of top gear though they managed to put the sporty 5 series beemer diesel around their track quicker than they could get the same year M5 around it.

 

Yeah i saw that too, not sure it was an M5 but certainly a much bigger petrol engine than the diesel.

 

- why aren'y diesel engines high reving ? is it to do with the way diesel ignites compared to petrol ? (i.e. 95 RON compared to 98 RON)

 

This is why V8's make a good engine. They have lowish rev's but have a high tourque through out their rev range.

 

so a lighter car, say honda Type R, can get away with reving so high but would need to keep the revs up to make the most of the performance ?

[dangerous brain]

- why aren'y diesel engines high reving ? is it to do with the way diesel ignites compared to petrol ? (i.e. 95 RON compared to 98 RON)

 

 

 

so a lighter car, say honda Type R, can get away with reving so high but would need to keep the revs up to make the most of the performance ?

 

I believe that older diesels don't rev high because they are very cheaply designed and manufactured engines. Attention isn't really given hugely to balancing commercial vehicle engines so taking said engines to high rpm wasn't an issue. Expect however serious development in this area real soon though.

 

Yep a teg type R will zip around like a pissed off wasp. Stick 4 people in it and fill the paltry luggage space with beer and see just how quick it is then. Torque is all if you intend on having more than just yourself in the car

[TrickTT]

I believe that older diesels don't rev high because they are very cheaply designed and manufactured engines. Attention isn't really given hugely to balancing commercial vehicle engines so taking said engines to high rpm wasn't an issue. Expect however serious development in this area real soon though.

Not totally true. Diesels need big heavy pistons and rods to withstand the huge combustion pressure ( diesels typically run over 20:1 compression ratio), so recipriocating mass is a factor in max rpm. In truck or large cc engines, each cylinder is displacing at least 1.5 litre (eg a 12 litre, 6 cylinder engine has a piston displacement of 2 litres, compared to 500cc or less for an average car - including a supra) so as a rule the stroke is much longer - diesels tend to run under square (stroke> bore) engines anyway. That is ideal for huge torque but it does mean that mean piston speed can get very high as revs increase. Keeping mean piston speed down is good for engine longevity as it places less stress on rods and big and little end bearings.

[dangerous brain]

I bow to superior knowledge on this matter. I assumed it was down to low tolerance engineering and thats why newer more developed engines were increasing power levels easily like the VW unit that first pushed past 150 bhp.

[Suprasteve]

Yep a teg type R will zip around like a pissed off wasp. Stick 4 people in it and fill the paltry luggage space with beer and see just how quick it is then. Torque is all if you intend on having more than just yourself in the car

 

so for argument sake my car will have more chance of beating a motorbike accelerating from a standing start if we raced up a very steep hill ?

 

using this same principle is this why a motorbike can accelerate at silly 0-60 speeds in comparison to a car but the higher the speed where wind resistance comes into play the difference is less due to the lack of torque.