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Bhp / ton



  E91 M Sport
Why is it that BHP/ton is quoted in the motor industry and not NM/ton? Does torque not have a direct relation to the weight of a car like the power does? As diesels become more powerful, I'd have thought this figure might be more telling....?

*awaits a geeky answer*
 
Both matter. Put simply, I think the majority of the public don't understand either of them. Pub bragging rights have always been about bhp and, more recently with the growing number of derv pervs, torque. "Yeah man it's got more torqz than da Boxter innit" :D

Adding torque per ton quotes would confuse them even more.
 
  Meg on pistonheads £6995
both are quoted in AutoCar tests

the lb/ft per ton is the one for me

truckloads of both even better ;-)
 
well can sum1 help me out, my clio is 100% standard and running 75bhp, since i have stripped out the back seats, spare wheel, soon to be all the back interior ie all plastics and carpets, have no ice at all, what bhp/ton and i running, please help people.
 
  Scirocco GT 210
well can sum1 help me out, my clio is 100% standard and running 75bhp, since i have stripped out the back seats, spare wheel, soon to be all the back interior ie all plastics and carpets, have no ice at all, what bhp/ton and i running, please help people.


You'll have to estimate how heavy your car is first.

Then:

BHP divided by car weight (in KG) = 'X'

Then multipy this 'x' figure by 1000.

This is your bhp/ton.
 
  Meg on pistonheads £6995
83bhp/tonne

woo hoo, I can beat a performance figure for a change!

980kg and 106bhp minimum = 108/tonne

980kg and 172lb/ft = 175/ton (a 197 @ 1240kg with 155lb/ft is ONLY 125!)
 
so does that mean my car is doing 83.3hp or seems like it is?
is always a bit confusing to me lol

It's just a relative figure. It means a lot more than just talking BHP figures. For example the 197 allegedly has 194bhp, but it's slower than a 182 because it's heavier. Well that and the fact that it's designed to be slower.
 
  Clio v6
222.85714285714285714285714285714 bhp per metric tonne.

I wonder if has any relation to my auto wipers being intermittently intermittent.
 
Why is it that BHP/ton is quoted in the motor industry and not NM/ton? Does torque not have a direct relation to the weight of a car like the power does? As diesels become more powerful, I'd have thought this figure might be more telling....?

*awaits a geeky answer*


The issue with torque is that it is a pure measurement of power or force, for example, if you were to hold a car from moving whilst he was applying full throttle (silly and impossible, but for arguments sake), and the wheels didnt move (nor did the engine technically), it would still be applying a force and putting power on you of say 150lb.ft, but it would be making zero bhp as no work was being done

If it were then released and set off at 5000rpm it would be making 142bhp........if it held 150lb.ft at 9000rpm, then it would be making 257bhp. This is because bhp is a measure of 'work done'.

If you were to use torque/ton as a measure of performance you would have no clue asto how much work it would be able to do (acceleration). Hence BHP is used as you can gauge the ability of the engine to work with a fixed weight.
 
Have a read of this. If you thought BenR was bad these geeks will really confuse you.

http://www.blatchat.com/t.asp?id=105088&pn=1&ps=15&c=

Its about bhp per litre but slates the mototring industry for there use of various units of measure for cars

You can see where its going, but using valve area/bhp is a measure of engine efficiency not vehicle performance.......stick the same ratio into 1 500kg car and a 1000kg car and the performance will be suitably different.
 
a static force that does not cause displacement is not work done, or so i was tought at school! lol
 
You need torque to tow a tank, but you also need bhp to tow it quickly. That's my take on it.

Torque is a twisting force. So 150lbs/ft is the same as adding a 150lb weight to a bar 1ft long on the crankshaft, for example.
 
  Nissan 350Z
Problem with using torque is that torque at the wheels depends heavily on gearing. Just because a DERV has 200 lb ft of torque doesnt mean much - it has to have taller gearing because it has less revs to play with than a petrol.
 
  megane coupe F7R
2 cars with same bhp but one has more torque.

Both do a sprint to 100mph and get there in the same time.

Then both do a sprint to 100mph, each pulling a heavy trailer.

The one with more torque will get to 100 first.

Thats my take on it, torque is pulling power. Thats why th yanks love thier big engines.
 
  172 ph1
2 cars with same bhp but one has more torque.

Both do a sprint to 100mph and get there in the same time.

Then both do a sprint to 100mph, each pulling a heavy trailer.

The one with more torque will get to 100 first.

Thats my take on it, torque is pulling power. Thats why th yanks love thier big engines.

If two identically weighted cars with the same power, same gearing, aerodynamics etc. (but one with more torque) get to 100 in the same time, it doesn't matter how much weight you put in the trailer, they will always get there in the same time.

To have accelerated to 100 in the same time as each other they must have had identical torque at the wheels over the rev range used.

That's what your gearbox is for, to convert the engine power into differing amounts of wheel torque at a given rpm.

In the real world you are right though, the car with more torque will be quicker somewhere, though not necessarily in the rpm range used for maximum acceleration.
 
  megane coupe F7R
2 cars with same bhp but one has more torque.

Both do a sprint to 100mph and get there in the same time.

Then both do a sprint to 100mph, each pulling a heavy trailer.

The one with more torque will get to 100 first.

Thats my take on it, torque is pulling power. Thats why th yanks love thier big engines.

If two identically weighted cars with the same power, same gearing, aerodynamics etc. (but one with more torque) get to 100 in the same time, it doesn't matter how much weight you put in the trailer, they will always get there in the same time.

To have accelerated to 100 in the same time as each other they must have had identical torque at the wheels over the rev range used.

That's what your gearbox is for, to convert the engine power into differing amounts of wheel torque at a given rpm.

In the real world you are right though, the car with more torque will be quicker somewhere, though not necessarily in the rpm range used for maximum acceleration.


Yeah i know mate :) I was tryin to make it simple to understand so people who dont know, get an idea of what torque is.

Cheers :)
 
2 cars with same bhp but one has more torque.

Both do a sprint to 100mph and get there in the same time.

Then both do a sprint to 100mph, each pulling a heavy trailer.

The one with more torque will get to 100 first.

Thats my take on it, torque is pulling power. Thats why th yanks love thier big engines.

Yup, it's a twisting force. In cars that means at the crank. The higher the torque, the more the crank can twist, but with more power it can twist it faster.

As I keep saying, you only need lots of torque if the engine is powering something heavy and has lots of work to do. The classic proof is a superbike that has MENTAL bhp/ton but sod all torque.
 
Last edited:
  RenaultSport clio 172 mk2
Why is it that BHP/ton is quoted in the motor industry and not NM/ton? Does torque not have a direct relation to the weight of a car like the power does? As diesels become more powerful, I'd have thought this figure might be more telling....?

*awaits a geeky answer*

power to weight is a useful measure because it tells you what acceleration times the cars is capable of. Of course to get those best times you have to rev the engine out to the revs it produces its maximum power at in each gear.

torque to weight isn't a very useful measure by itself but in conjunction with power to weight it tells you quite a lot. If a vehicle with a low power to weight but a high torque to weight - like an American V8 or a European turbo diesel or a truck - can be quite a good tow vehicle, even if you don't get there very fast. A vehicle with a high power to weight but a low torque to weight - like a racing car - can get where its going quite quickly by wringing its neck, but will be a real pain to drive when you don't because it'll be gutless unless you change down and use all the revs. The most pleasant vehicles to drive normally have at least a good torque to weight ratio.

Of course its also important where in the rev range that torque is developed, and how wide the band of torque is. A V8 or turbo diesel or low-boost pedtrol turbo might be producing its maximum torque at 1500 rpm, whereas an F1 engine might be producing its at 16,000 rpm. The ideal for easy driving is what you get in a low boost turbo where you get a really wide flat torque band. The ideal for fun is when you get that kick at a certain speed like the Clio Sport does when it comes on-cam at 4500 rpm.

That's why a simple figure of torque to weight doesn't tell you anything by itself. Whereas at least power to weight predicts performance.
 
  RenaultSport clio 172 mk2
Have a read of this. If you thought BenR was bad these geeks will really confuse you.

http://www.blatchat.com/t.asp?id=105088&pn=1&ps=15&c=

Its about bhp per litre but slates the mototring industry for there use of various units of measure for cars

Mark's posting is relevant because it talks about guys trying to get lots of power out of a 1.9 litre Rover K-series engine, and that engine is similar in a lot of ways to the Clio Sport. Its about the same vintage in terms of when it was designed. Its a longish-stroke four-valve twin-cam four designed to a maximum of 1.8 litres that's been stretched to 2 litres by stroking it. They are similar engines. Guys like edde and Fred with a lot more practical and mechanical experience than I have with the Renault engine would be the ones who could tell us whether it has limitations like small valves or poor port shape or wall thickness or a weak bottom end or something else that would prevent it producing similar power to the Rover K at similar revs.

Its relevant to the original posters question because it talks about the difficulty in getting lots of horsepower out of a relatively small-bore long-stroke engine, because it is valve size that dictates power. As someone points out on that other forum the 1.3v litre Suzuki Hayabusa bike engine and the 1.9 litre Rover (and as it happens the Renault) have the same bore so they have the same valve size so they're capable of being developed to about the same maximum power. The Suzuki just does it at a lot higher revs. The Rover and the Renault will never win the sort of pissing competitions we see on web sites for who can develop the most power, or the most power per litre, or how high they can rev, because they're long stroke engine. That's why Ford with its shorter-stroke big-bore engines has been the traditional base for racing engines for motorsport companies like Cosworth. But long stroke engines like the Rover and Renault produce better torque at lower revs so they are better road car engines, and they have a better surface to volume ratio in the combustion chamber so they can run higher compression ratios for better torque and better specific fuel consumption, and lower emissions.

Short stroke engines like Ford builds are better race engines. Lots of power, who cares that they don't produce a lot of torque, or if they do its way up the rev range.

Longer stroke engines like the Rover and Renault are better road engines. Lower maximum revs. Not as much peak power. More peak torque at lower revs with a wider flatter torque band. Better fuel consumption.
 


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