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- Thread starter W2S
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graz_lag
Major Contributor
... Unless you want to pull a caravan ...
For which again you need power. True, you need a lot of it at low RPMs, and to have that you need torque. But again, it is the power doing the work, not torque.
For streets and traffic I value torque more than power. Typical normal driving rpm is 1000-2500rpm.
335D >150hp at 1600rpm
3.0si (no turbo and this must be at tires) I have this engine (98oct) in my X3 -07 and it only starts pulling well above 4500rpm when secondary intake ports open. >150hp at 4000rpm
335D >150hp at 1600rpm
3.0si (no turbo and this must be at tires) I have this engine (98oct) in my X3 -07 and it only starts pulling well above 4500rpm when secondary intake ports open. >150hp at 4000rpm
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If the torque curve were really flat to say 5000 rpm, then you would really have something. And it is still the power that is doing work for you.For streets and traffic I value torque more than power. Typical normal driving rpm is 1000-2500rpm.
335D >150hp at 1600rpm
3.0si (no turbo and this must be at tires) I have this engine (98oct) in my X3 -07 and it only starts pulling well above 4500rpm when secondary intake ports open. >150hp at 4000rpm
Wrong.
An old colleague used to ask interviewees for an engineering post whether power or torque were more important as his first question. Anybody saying torque was politely dismissed without any other questions.
Brutal but quite right.
Sorry, but you are still valuing power - it is just you don't realise itFor streets and traffic I value torque more than power. Typical normal driving rpm is 1000-2500rpm.
335D >150hp at 1600rpm
3.0si (no turbo and this must be at tires) I have this engine (98oct) in my X3 -07 and it only starts pulling well above 4500rpm when secondary intake ports open. >150hp at 4000rpm
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I like a broad reasonably flat torque curve for street cars. Not hard to find in most modern cars. Power scales pretty well with rpm. I think of some odd cars in this regard I found not fully satisfying.
One is the early version of the Honda S2000. 10,000 rpm red line and max power that was very good for engine size. The V-tech variable valve timing however, changed and torque along with power jumped about 20% right at 6000 rpm. So it felt a little anemic below that. Which could encourage you to drive it more aggressively (and it was too fast to do that safely often). The later version was 8500 rpm redline and still had a bump around 5 or 6k rpm, but was more powerful below that range than the early S2000. So you didn't feel the need to thrash it just to keep up with econocar traffic starting off from traffic lights. Also the early version S2000 was too tail happy.
The other is the goofy 1981 Turbo Trans Am. Turbocharged 4.9 liter V8. And it was redlined at 4500 rpm. So it had gobs of torque and power if you floored it, but just when its getting good, boom you run out of rpm(and boost) and either shift or the driving power isn't increasing at all. Almost the opposite of the early S2000.
One is the early version of the Honda S2000. 10,000 rpm red line and max power that was very good for engine size. The V-tech variable valve timing however, changed and torque along with power jumped about 20% right at 6000 rpm. So it felt a little anemic below that. Which could encourage you to drive it more aggressively (and it was too fast to do that safely often). The later version was 8500 rpm redline and still had a bump around 5 or 6k rpm, but was more powerful below that range than the early S2000. So you didn't feel the need to thrash it just to keep up with econocar traffic starting off from traffic lights. Also the early version S2000 was too tail happy.
The other is the goofy 1981 Turbo Trans Am. Turbocharged 4.9 liter V8. And it was redlined at 4500 rpm. So it had gobs of torque and power if you floored it, but just when its getting good, boom you run out of rpm(and boost) and either shift or the driving power isn't increasing at all. Almost the opposite of the early S2000.
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No offense, but this statement doesn't make sense. You may prefer certain torque curve which then dictates power curve, but it is always the power that accelerates your car.
Maybe the gearing was too short for such narrow RPM working range. Or maybe it was made like that purposely to have better acceleration.
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Gearing was actually rather high. It was to meet pollution requirements at the time. It passed those with the EPA test cycle. The turbo didn't do anything. You drive it harder and the turbo supplied a considerable amount of boost. But at 4500 rpm the boost dropped.
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It is better for the engine to develop power at lower RPMs as friction losses are rasing with square of RPMs. The rest you fix with gearing.
graz_lag
Major Contributor
People have opinions yes, but physics is simple Power= torque x rpm
https://www.engineeringtoolbox.com/angular-velocity-acceleration-power-torque-d_1397.html
Speaking about tractors, there is concept of torque rise, which gives character to the engine
https://www.perkins.com/en_GB/products/engine-performance/torque-backup.html
Free-breathing engines are pretty much different animals from turbos, specifically the modern consumer models that start boosting at very low rpm. BMW 335D has two turbos like many modern petrol engines too, one for low rpm and other for high rews.
By the way how many of you have ridden 2-stroke racing bikes? Talking about acceleration and peakiness!
https://www.engineeringtoolbox.com/angular-velocity-acceleration-power-torque-d_1397.html
Speaking about tractors, there is concept of torque rise, which gives character to the engine
https://www.perkins.com/en_GB/products/engine-performance/torque-backup.html
Free-breathing engines are pretty much different animals from turbos, specifically the modern consumer models that start boosting at very low rpm. BMW 335D has two turbos like many modern petrol engines too, one for low rpm and other for high rews.
By the way how many of you have ridden 2-stroke racing bikes? Talking about acceleration and peakiness!
What is linear force and distance in rotation scenario is torque and angle.
So in rotational scenario work is done by torque on angle, the same as it is done by force on a distance. (W=F*s)
Work always equals the ammount of energy necessary to move object from one point to another (measured by distance or by angle).
So where power comes to play? When you introduce TIME.
If you want to move object in shorter time you will need more power. Less powerfull car will also do the job, but in more time.
Once you accept that concept it becomes clear that power=work/time. In other words power is a rate at which the work is done.
So, once you know what kind of work needs to be done at which ammount of time you get the power necessary to do it.
I believe it is now clear it is the power which accelerates the car, not torque/force.
P.S. It should also be noted that power is needed if you drive at constant speed as well. In that scenario work is also used (as time passes by!) to move the vehicle from one point to another while also fighting air resistance and friction forces.
IMHO opinion, specifying peak power figure and peak torque is BS - what you really need to see is power vs RPM graph and from there you can get the idea what the engine can do. @Frank Dernie , would you agree?
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The power/rpm graph is interesting. It tells how many gears you need and where is the optimum shift point. A broad torque curve is easiest to drive but won’t give the best performance.
As a simple example. Imagine 2 engines one giving 100ft-lb of torque at 2000 rpm, the other giving 50 lb-ft of torque at 4000 rpm.
Both have the same power, since the higher torque model needs gearing twice as high to do the same speed the thrust at the tyre is the same, since the power is the same. That is all that counts.
Torque is used to calculate power, without speed it tells nothing, an engine producing infinite torque at zero rpm is producing no power and going nowhere.
As a simple example. Imagine 2 engines one giving 100ft-lb of torque at 2000 rpm, the other giving 50 lb-ft of torque at 4000 rpm.
Both have the same power, since the higher torque model needs gearing twice as high to do the same speed the thrust at the tyre is the same, since the power is the same. That is all that counts.
Torque is used to calculate power, without speed it tells nothing, an engine producing infinite torque at zero rpm is producing no power and going nowhere.
That is indeed so, unless your engine is electic motor - as they have torque at 0 RPM they will actually start going even from 0 RPM. That's why we used them as starters for poor old internal combustion engines which really can't go anywhere at 0 RPM.
I have a plug-in hybrid which is very sprightly from low speed but it also isn’t going anywhere at 0 rpm, and once the car is moving it is still the power curve which counts.That is indeed so, unless your engine is electic motor - as they have torque at 0 RPM they will actually start going even from 0 RPM. That's why we used them as starters for poor old internal combustion engines which really can't go anywhere at 0 RPM.
How do you get it going then? With gasoline engine?
Anyway, electric motor will move from standstill the same way the electric starter in your car gets going from standstill to start your gasoline engine. It only has to hae enough force (torqu) to move a little. As DC motors have pretty much flat torque curve all the way to max RPMs the power will raise in a linear fashion as the motor gains RPMs.
