Driving torque

[CitizenErazed]

Ok, I was thinking about this last night, I looked at my car stats and it said maximum torque was measured at 4,000 RPM, though it didn't say in what gear -.- and it got me thinking that for optimum performance surely I should be looking at my torque charts to see when the best time to change gear? I mean, not changeing as soon as I hit maximum torque for that gear, maybee for instance even though 4,000 is max, 5,000 may be better then the equivilent in the next gear up so it'd be worth staying in that gear a while longer before change.

Is this idea right or have I just thought up a load of twisted logic crap?

Someone I used to work with (boy racer) used to say, knowing when to change gear for speed was easy, go to the end of the redline then change. Though I'm sure thats going to damage the engine, my redline starts at 6,500 RPM, I don't go near that. So is he right or am I right and he's just damageing his car to drive slower?

If I am sorta right BTW, how do I find out how mods change my torque curves? I mean my induction kit, sucking hot air under my bonnet will probably have reduced preformance but I still wana know how it's effected the torque curves so I can see when's better to change gears now. I'm still trying to find the torque charts for my car factory standard actually


Don't know if I made any sense there or if I'm not just talking nonsense

 

[pgarner]

Torque is the main product that the engine gives. the power is in a way the by product.

easiest way is calculate power is =

torque in lbft x current rpm
---------------------------
5252

as for what gear? most manufactures will give you the power / torque at the flywheel as this looks better. so gear doesnt really matter

your mates talking crap for most cars.
you want to be changing up so after the change your coming into peak power.
for example is peak power is around 5700 rpm and you have around 500 rpm between the gears then you should be looking to change around 6200rpm.
on some cars yes you do need to go to the limiter but its wasting time as the engine will cut the power back as you hit it costing time.
also remember that power tails off sharply towards the end

in a diesel however your wanting to change up after peak torque.

 

[pgarner]

sorry about those double posts if you seen them.

youve also got to remember that power normally tails off sharply towards the end of the rev range

 

[HDi fun]

Every engine/gearbox/vehicle combination is different.

It's torque that makes the car accelerate. But that doesn't mean changing up earlier because a lower gears gives more road wheel torque than a higher one.

You're unlikely to damage the engine by using all the revs. Keep it serviced and don't work it too hard when it's cold.

 

[MasterAuron]

You're unlikely to damage the engine by using all the revs. Keep it serviced and don't work it too hard when it's cold.

This is very true. Most engines can rev a fair bit higher than the set limit, that limit is just imposed by the manufacturers to prolong the engine. Of course, if you're redlining a standard engine all the time you drive, every day, many engine components will wear more quickly because of the increased vibration at higher revs. Manufacturers tolerances aren't always the strictest

 

[Sid447]

Ok, I was thinking about this last night, I looked at my car stats and it said maximum torque was measured at 4,000 RPM, though it didn't say in what gear -.- and it got me thinking that for optimum performance surely I should be looking at my torque charts to see when the best time to change gear? I mean, not changing as soon as I hit maximum torque for that gear, maybe for instance even though 4,000 is max, 5,000 may be better then the equivilent in the next gear up so it'd be worth staying in that gear a while longer before change.
Is this idea right or have I just thought up a load of twisted logic crap?

Someone I used to work with (boy racer) used to say, knowing when to change gear for speed was easy, go to the end of the redline then change. Though I'm sure thats going to damage the engine, my redline starts at 6,500 RPM, I don't go near that. So is he right or am I right and he's just damageing his car to drive slower?

If I am sorta right BTW, how do I find out how mods change my torque curves? I mean my induction kit, sucking hot air under my bonnet will probably have reduced performance but I still wana know how it's effected the torque curves so I can see when's better to change gears now. I'm still trying to find the torque charts for my car factory standard actually
Don't know if I made any sense there or if I'm not just talking nonsense

Generally,

for maximum progress you shift up at or just past the maximum rpm and this should (as long as the gear ratios aren't too widely spaced) drop the revs back to around where maximum torque occurs.

e.g. If an engine develops peak power @ 5,800rpm and peak torque is made at 4,000rpm (meaning it has an 1,800rpm power band...4,000 to 5,800rpm)
...then usually changing gear 2 or 300rpm past peak power (~6,000 in this example) to allow for the time it takes to complete the gearchange ...and the revs should, if the ratios are well chosen drop back to around or just above peak torque.
This allows the fastest progress in most cases.

An ideal engine using this anology would have a nice big gap between peak power and peak torque (e.g. peak power @ 6,200 and peak torque at say 3,500rpm. This would mean you have a nice wide 2,700rpm power band -3,500 to 6,200rpm). But this is quite difficult to achieve in modern 4-valve small capacity stuff. Variable cam phasing tries to address this particular thing exactly.

For normal and economy-minded driving you don't need to do this at all, as you know.

In answer to how torque is measured and what gear.........it's done on a manufacturers engine dyno, so no gearing involved.

How can you tell how the mods have affected it...........have it run on a chassis dyno and ask for the rear wheel figures to be corrected to either J607 or J1349 standard (J607 is the one still widely used, J1349 will read about 4% lower) Chassis dynos only measure wheel hp so are subject to drivetrain loss.
The only way to get flywheel hp is to either have the engine removed and run on an engine dyno or compute the flywheel figure from the rwhp figure which is usually (if it's a manual car) here:-

http://www.pumaracing.co.uk/trans.htm

other good links...................


http://www.pumaracing.co.uk/POWER1.htm

http://www.pumaracing.co.uk/gentune.htm

 

[turbonutter69]

Generally,

for maximum progress you shift up at or just past the maximum rpm and this should (as long as the gear ratios aren't too widely spaced) drop the revs back to around where maximum torque occurs.

e.g. If an engine develops peak power @ 5,800rpm and peak torque is made at 4,000rpm (meaning it has an 1,800rpm power band...4,000 to 5,800rpm)
...then usually changing gear 2 or 300rpm past peak power (~6,000 in this example) to allow for the time it takes to complete the gearchange ...and the revs should, if the ratios are well chosen drop back to around or just above peak torque.
This allows the fastest progress in most cases.
An ideal engine using this anology would have a nice big gap between peak power and peak torque ideally (e.g. peak power @ 6,200 and peak torque at say 3,500rpm. This would mean you have a nice wide 2,700rpm power band -3,500 to 6,200rpm). But this is quite difficult to achieve in modern 4-valve small capacity stuff. Variable cam phasing tries to address this particular thing exactly.

For normal and economy-minded driving you don't need to do this at all, as you know.

In answer to how torque is measured and what gear.........it's done on a manufacturers engine dyno, so no gearing involved.
How can you tell how the mods have affected it...........have it run on a chassis dyno and ask for the rear wheel figures to be corrected to either J607 or J1349 standard (J607 is the one still widely used, J1349 will read about 4% lower) Chassis dynos only measure wheel hp so are subject to drivetrain loss. The only way to get flywheel hp is to either have the engine removed and run on an engine dyno or compute the flywheel figure from the rwhp figure which is usually (if it's a manual car) here:-

http://www.pumaracing.co.uk/trans.htm

other good links...................


http://www.pumaracing.co.uk/POWER1.htm

http://www.pumaracing.co.uk/gentune.htm

I always thought rolling roads did the flywheel figure first and then convert the mechanical drag to get the actual bhp at the wheels?

 

[HDi fun]

The rr dyno measures the torque at the wheels, from which bhp at wheels is easily calculated.

The losses in the transmission are measured when the clutch is dipped (keeping the car in gear) so that the system can measure the reverse torque whilst speed is lost.

It's not perfect but it is repeatable so you get some pretty accurate figures this way.

I remember the dyno run my car underwent in Jan 2007. The noise is incredible in an enclosed space with the car running at full load, the turbocharger screaming at full boost.

 

[Sid447]

An engine dyno test example:-

http://www.youtube.com/watch?v=hNzsz3llg0A

Chassis dyno or rolling-road dyno.............

http://www.youtube.com/watch?v=mJetaet1YPE

 

[Munday]

And if you can choose your own gear ratios....torque doesnt matter at all, its all about the power. :bigsmile:

 

[HDi fun]

And if you can choose your own gear ratios....torque doesnt matter at all, its all about the power. :bigsmile:

Nope. It's torque that moves the car. All you do is choose ratios to deliver as much torque as possible to the wheels.

 

[Munday]

Nope. It's torque that moves the car. All you do is choose ratios to deliver as much torque as possible to the wheels.

Its the torque to the wheels that moves the car...and that torque is determined by the gear ratios and the engine power. Why are hondas so quick when they have hardly any torque? Revs and gear ratios.

Its a fact that engine torque is largely irrelevant IF you can choose the right gear ratios

 

[MasterAuron]

Why are hondas so quick when they have hardly any torque? Revs and gear ratios.

I made this point in another thread. Come on HDi, you know better than that

 

[turbonutter69]

Torque obviously is not everything when it comes to power in a car.
Look at a diesel. They have loads of Torque but put a petrol against it with less torque and more BHP and which would win?
I think everyone knows it would be the petrol with less Torque but more BHP.

 

[Sid447]

Torque accelerates you,

Hp decides your maximum speed. You can't have one without the other.
A post in LS1tech said it brilliantly for my sense of humour....Horsepower is how fast you hit the wall, torque is how far you take the wall with you.........

Seriously though, you could for an example fit a 150hp 65lb-ft Yamaha R1 1,000cc engine in a 1000kg car and given enough gears (probably about 12 for reasonable torque multiplication and even spacing) it would win an acceleration race assuming it was using full rpm (i.e. about 15,000). against a similar weight car with a turbo-charged 2-litre of about 250lbs-ft of torque and 200hp which had the normal rpm limit of around 6,500rpm.
Though the turbo car would initially be ahead to about 30 or 40mph because of the better torque (response) off the line. Whereas the bike engine would need to be screamed to the red-line to take full advantage of it's abilities.

You need as much torque as early as possible and for as long as possible.
Turbo-diesel cars make great torque from low rpm but are limited to a max of around 5,000 revs. This makes them ideal for city/town traffic and 30-70mph acceleration which is real-world stuff.
But normally a high-revving or large capacity petrol-powered car can be made to make as much torque as any diesel powered car by about 3,000 to 4,000rpm and it still has another 2,500 rpm or so of useable power-band to play with, which will make it quicker in the long run.

Different strokes for different folks, Not everyone though wants to be first to the flag.

 

[turbonutter69]

Not everyone though wants to be first to the flag.

But if you do then buy a petrol.

 

[HDi fun]

Because they rev high and can therefore use shorter gear ratios. Thus increasing the torque at the wheels.

Torque is a force. Power isn't And you need a force to set something in motion.

At any given moment, if you ignore transmission losses the flywheel power and roadwheel power are indentical. Regardless of which gear you're in.

 

[Munday]

Because they rev high and can therefore use shorter gear ratios. Thus increasing the torque at the wheels.

Torque is a force. Power isn't And you need a force to set something in motion.

At any given moment, if you ignore transmission losses the flywheel power and roadwheel power are indentical. Regardless of which gear you're in.

Which is exactly why power > torque

Torque X RPM
_______________ = power

5252

 

[HDi fun]

Power and torque cannot be compared. They're not the same thing.

It's like trying to compare miles miles per hour with litres.

The power in the system is the same at roadwheels and flywheel. The difference will be the torque at each and revs per minute. And it's the choice of giear that dictates this ratio.

What your banging on about power being greater than torque is utter nonsense.

Power is a measure of the rate at which work is done and necessarily involves an element of time.

Torque is simply a rotational force.

 

[Munday]

Power and torque cannot be compared. They're not the same thing.

It's like trying to compare miles miles per hour with litres.

The power in the system is the same at roadwheels and flywheel. The difference will be the torque at each and revs per minute. And it's the choice of giear that dictates this ratio.

What your banging on about power being greater than torque is utter nonsense.

Power is a measure of the rate at which work is done and necessarily involves an element of time.

Torque is simply a rotational force.

Power and torque cannot be compared? Power is calculated from torque! So thats that out of the window.

What ive been saying all along was saying that at the FLYWHEEL the torque is pretty much irrelevant, as the gear ratios dictate the torque applied to the wheels. Im not saying the torque at the wheels is not important

 

[HDi fun]

It's possible to have torque at 0 rpm in the case of a series wound DC electric motor. Put it's producing no power because it's not rotating.

Like wise you can have an engine on a bench running at a constant 6000rpm but there's no torque output as such so therefore it's doing no useful work and in turn means the power output is nil.



As I said, power has an element of time built in, torque is just a force. The time element comes from RPM ie revs per MINUTE!!

So you cannot compare them directly as they are not the same thing.

have a look at this wiki, which explains it very well indeed:

http://en.wikipedia.org/wiki/Torque

 

[Munday]

It's possible to have torque at 0 rpm in the case of a series wound DC electric motor. Put it's producing no power because it's not rotating.

Like wise you can have an engine on a bench running at a constant 6000rpm but there's no torque output as such so therefore it's doing no useful work and in turn means the power output is nil.



As I said, power has an element of time built in, torque is just a force. The time element comes from RPM ie revs per MINUTE!!

So you cannot compare them directly as they are not the same thing.

And torque has an element of distance built in, im not directly comparing them. You cant deny that power HAS to be compared to torque when considering an engine...as it will always be moving at a certain rpm.

The only point i was making is IF you can choose gear ratios....Torque can be obtained from gear ratios and its power you want from the engine. You get that by having lots of revs

 

[HDi fun]

They are, as you say inextricably linked.

That's basically why we have gearboxes. If an engine could generate torque at standstill and carry on revving high enough to achieve a useable top speed then we'd never have invented gearboxes. Steam engines are a good example.

But it is possible to have loads of torque but no useful power. As per the DC motor. Sure it's converting electrical energy into heat energy if it's armature is clamped stationary and then current is applied. But it's not doing any useful work.

Incidentally, don't try this - it's bloody dangerous.