Hi

Read in this month Evo a long article about "What is torque" and one part of it was what is the best for optimium acceleration. They went down the route of Newtons laws and finally stated that for optimium acceleration you need to be at the highest Torque value (not highest power unless that happens to be the same revs).

This goes totally against the arguements which were discussed here quite a few months ago & agrees with my assumption at the time.

What they finally said was in the ideal world you would have CVT which would hold the revs at peak torque for all driving i.e. acceletation/maintaining speed.

If you have views please post & also before anyone goes off on one please read the article before.

I was pleasently surprised to be found correct.

Does this go back to changing up at peak torque for accelerating quickly - I don't read Evo any more so haven't read the article

Chris

Well thats the theory - as they said the optimium is to have a CVT which holds revs at peak torque (which is exactly what trains do...).

But surely changing gear at peak torque (below 2k in some diesels) is very uncomfortable for passengers and very bad for mechanical components?

Chris

I've always been under the impression that torque influenced acceleration, and power influenced ultimate top speed (as well as drag, traction levels etc. etc.)

According to NASA, though, horsepower is an integral function of torque, so theoretically one should be inextricably linked to t'other... I've also heard that the rev range has something to do with it, so a 16v petrol-engined car with, say, 100bhp will accelerate in gear less quickly than a 100bhp diesel-engined car, but because its engine will rev higher, it will have a higher top speed (theoretically.)

Having said all that, though, I can't think of many cars these days that can't break the speed limit, so top speed is kind of irrelevant - therefore IMO the 'fun factor' has to lie in acceleration's court...?

they are intrinsically linked.. but its largely irrelevant as the aero and weight of the vehicle will have so much "3rd party" effect that each individual vehicle will be different.. never mind the gearing....

But surely changing gear at peak torque (below 2k in some diesels) is very uncomfortable for passengers and very bad for mechanical components?

Chris

Yes thats the dilemma though in a manual as youd want to get the average revs to be at peak torque while a CVT would obviously remove any gear changes so it would be peak torque all the time.

peak power is where to change gear, torque is output of the engine but at higher revs the more often that torque is being applied which is where bhp was invented to compare different engines its all well and good making 1,000,000 lbft but if you can only rev to 2 rpm your only making 347bhp but if you can rev to 8,000 rpm you only need to be making 250lbft so its not simply torque but torque and where you make it.

Interesting debate.

Well I'm definitely a fan of torque!

I drive freight trains for a living,

3100bhp at 850rpm, but 138,000lb/ft of torque

Plus a nice "traction control computer"

that helps to sort out icy hill starts with 2500t

hooked on the back.

I'm not aware of anyone using petrol engines for this!

they use diesels simply for fuel economy reasons

and its "only" making 21,000lbft at that peak power

I'm not aware of anyone using petrol engines for this!

But a freight train isn't built for speed. Compare those stats to an F1 car which develops 700-900bhp and relatively little torque, all from a normally aspirated engine, and is capable of doing 200mph from a standing start in 8.5 seconds!

I'm still not convinced by the torque always wins argument, but if there's Evo maths to back it up, it must be true

Chris

torque doesn't always win, its where you make the torque and the gearing that dictates the speed of a vehicle

Agreed, Ben. I like the analogy of the bicycle but can't find the link at the mo, so this one will have to do dmiessler.com | study | horsepower

This is quite an interesting comment from that site...

"It is better to make torque at high rpm than at low rpm, because you can take advantage of gearing." -- The VetteNet Home Page

Chris

Well thats the theory - as they said the optimium is to have a CVT which holds revs at peak torque (which is exactly what trains do...).

My mum has a Jazz with CVT, and it makes for a comfortable and reasonably quick progress considering it's a 1.4. However, I gather CVTs can't handle much torque (being an elastic band running around two opposing cones after all), and I seem to remember that Audi(?) made a CVT transmission for a while, but it wasn't much of a success as the engines had to be de-tuned compared to their manual / 'conventional' automatic cousins... So if you COULD make a CVT capable of handling lots of torque, it would give the best performance, but because of the torque-handling limitations, DSGs etc. make for faster cars...

:iagree:

Here is good explanation.....

Description of a very simple model to predict vehicle performance from power to weight ratio alone

Using my car as an example. Before I upgraded the turbo, I had 305 ft lbs of torque, but at a peak rpm of 2600. Therefore, if I was alongside a more powerful but less torquey car - lets say for example a civic type R, on a roll I would easily out accelerate him if i was in my peak torque band, and he was in his. If however he was in his peak power band, and I in mine, he would easily out accelerate me, as apart from anything else, i would have to change gear.

Or - on a short twisty track, he wouldn't be able to pass me due to the beniefit of huge torque out of the corners. On a longer track with less tight corners, he would be able to easily pass me.

I think what we see in the real world is that if Im cruising off a round a bout and there is a vRS who gives it some stick at the same time as I give it some stick he will get the initial jump - however as the speeds increase I will then claw back the initial lost ground and overtake cleanly.

What does all this say with respect to the UK road networks.... well IMHO I cannot see the point in running petrol engines which produce less than 220bhp as the economy of the smaller power petrols & performance is dwarfed by a similar priced TDI.

What does all this say with respect to the UK road networks.... well IMHO I cannot see the point in running petrol engines which produce less than 220bhp as the economy of the smaller power petrols & performance is dwarfed by a similar priced TDI.

And likewise there is no point buying a car that is geared to travel at over 70mph because that is the UK speed limit. Therefore we should all drive around in 600cc Smart cars

Chris

And likewise there is no point buying a car that is geared to travel at over 70mph because that is the UK speed limit. Therefore we should all drive around in 600cc Smart cars

Chris

Bring on the Kei Car revolution!!!

:D :D

On the weekend I went to the Seat Dealership to have a look and they had a Cupra Leon 240bhp the speedo IIRC goes up to 170mph with 0mph at the 6pm position and 170mph at 3pm 70mph is roughly 9.30pm.

Now this to me is idiotic 30mph isnt that clear and Im not sure 20mph increment is marked. for the UK what is the point in a speedo like this?

Look at the old RS6 from 7pm =0mph to 2am = 80-90mph and then at 5pm = 185mph this makes total sense, when you watch you tube for the speedos on RS6's you'll see that it races up to 80-90 and then due to the change in increments it is vastly slower.

Doesnt the vRS have a sensible speedo for UK usage i.e. very clear up to 70mph and then it steps up in 20mph increments rather than 10mph? if so bloody good idea.

I'm having trouble understanding your clock positions as the 12 hour clock doesn't distinguish between am and pm :confused:

Chris

I'm having trouble understanding your clock positions as the 12 hour clock doesn't distinguish between am and pm :confused:

Chris

lol ah yes ignore the am & pm.

Chris I read your GT TDI140 review and it was very good - have you driven a GT TDI150 and if so do you have a similar review?

Not a standard one so didn't feel it was a fair comparison

Chris

Found on another site:

You are probably familiar with the terms 'horsepower' and 'torque', and it is highly likely that you have at least estimated these values for your engine. Both are regularly used in the car industry and are considered the 'norm' in terms of rating the performance of a car's engine, and people are happy to compare using these figures.

The question is though, what exactly are these units, and how do they relate to how well an engine can actually perform?

Horsepower (Bhp)

This is the value being quoted more often than not, and is generally used as the main comparison between engines. Horsepower can be calculated to decimal place accuracy, but the size of the horsepower is somewhat of an estimate.

The value of the horsepower was invented by James Watt (the same James Watt who gave us the watt value seen on light bulbs etc), and it is said the measurement was created while Watt was working with horses in a coalmine. Watt observed that, on average, one horse could provide enough force to lift 550 pounds 1-foot in 1 second. Another way of quoting the same value, and as used more commonly, is 150Lbs 220ft in 1 minute. This value is really more of an estimation, however considering the same standard unit is used when comparing power, it doesn't matter. Horsepower can also be converted into other units. For example, 1 horsepower is the equivalent to 746 watts.

So, as previously mentioned, horsepower is the most commonly used rating of an engine's performance, but how do you find out that rating? In order to calculate an engines horsepower, you need to know two values - the cars torque level (lbs-ft), and the engine speed (rpm).

Calculating Horsepower

This is where it gets a bit heavy on the maths, but you don't really need to understand how it's calculated, just accept that it works!

As stated earlier, the unit of 1 horsepower is to move 150Lbs, 220ft in 1 minute.

This can also be stated as 1 horsepower is the ability to do 33,000Lbs-ft of work in 1 minute. (Work = Force Applied x Distance Moved).

Watts definition came from a horse applying torque to a lever, so for an engine we need to imagine a 1ft lever attached to the crankshaft.

If the lever were to rotate 360

i got about 1/4 though that and got bored ****less.