Power vs Torque Questionnaire -RESULTS

[machin]

Now a few of you will have seen that in my signature for the past year or so I have had a link to a short Survey Monkey questionnaire about Power and Torque. I've now removed the link, and thought it only fair that I post the results for all to see. First I will remind people of the questions and give the answers in red below:

Q1: The rear wheels of a current F1 car spin at approximately 780rpm when travelling at 100kph. The rear tyres will not lose traction if the torque applied to the wheels is less than 2000 lbft.You have the option of three different engines, which can generate the following amounts of torque at the indicated engine speed, and each is geared to match the engine RPM shown with the wheel RPM at 100kph. Which engine(s) will lose traction if full throttle is applied?

Engine A: 120 lbft at 9000rpm (Torque at driven wheels = (9000/780) x 120 = 1384 lbft, 1384<2000 therefore this engine will not lose traction)
Engine B: 230 lbft at 7000rpm (Torque at driven wheels = (7000/780) x 230 = 2064 lbft, 2064>2000 therefore this engine WILL lose traction)
Engine C: 680 lbft at 2250rpm (Torque at driven wheels = (2250/780) x 680 = 1961 lbft, 1961<2000 therefore this engine will not lose traction)

The second question was simply a repeat of the first but with all figures converted from torque to power:-(BHP = (Lbft x RPM)/5252).


Q2: The rear wheels of a current F1 car spin at 780rpm when travelling at 100kph. The rear tyres will not lose traction if the power applied to the wheels is less than 297bhp (2000 lbft x 780rpm / 5252).You have the option of three different engines, which can generate the following amounts of Power, and each is geared to match the power shown with the wheel RPM at 100kph. Which engine(s) will lose traction if full throttle is applied?

Engine A: 205 bhp ((120 lbft x 9000rpm) / 5252) (205<297 therefore this engine does not lose traction)
Engine B: 306 bhp ((230 lbft x 7000rpm) / 5252) (306>297 therefore this engine DOES lose traction)
Engine C: 291 bhp ((680 lbft at 2250rpm) / 5252) (291<297 therefore this engine does not lose traction)

As you can see, the correct answer in both cases (as you would expect considering they are the same question!), is Engine B.

Now on to the results:

44% of people got Question 1 (with the question written in terms of Torque) correct. Which is very encouraging.

51% got question 2 correct (with the question written in terms of power).

I have now updated my signature with a new link to a new Power vs Torque quiz, this time the basis of the question is the actual performance of two similar Mercedes saloons as tested by Autocar Magazine (note: these are not theoretical results, but actual road test results)... more importantly the new link gives instant feedback, so you'll know straight away whether you answered the question right or wrong. Thanks for participating.

Machin

[Just_a_fan]

So the best engine for acceleration is engine C? The one that gets closest to spinning the wheels but doesn't actually spin them.

[machin]

...personally I'd always go with the one having the best power (not just peak power, but throughout the rev range) and then simply use less throttle when you are traction limited.... Thus giving you more power when traction does allow....

With nothing more to go on (in this instance) engine B would be my choice.

[Just_a_fan]

Best power throughout the rev range is the same as best torque throughout out the rev range, of course, because the highest power at any given engine speed will also be the highest torque. Which goes back to the discussion of a few months ago.

The real issue is whether one is racing or driving to the shops. The shape of the engine's power/torque curves is then an issue.

[Jolle]

I've driven a few of the same type of cars with different engines, for instance the BMW E92 325i and 335i, both automatics.The 335i has a huge amount of torque from 2.000 rpm, while the 325i needs more revs. I found the 335i the best for lazy driving, but fast. From any gear always lots of speed, while the 325i was much more fun to drive (although slower), but for normal commuting not as comfortable.

But in most cases it's what you like and what kind of car/character suits you. I've always been a fan of big twin cylinder motorbikes (like the BMW R-series or Ducati's) and diesel cars with big turbo's (I drove a MB W204 320CDI for a few years, tuned to 600Nm torque and 275 HP, the TC was my best friend) and other people like the high revving Honda's

[machin]

Best power throughout the rev range is the same as best torque throughout out the rev range

Not if the two engines have different rev ranges... For example a Diesel engine, with lots of torque might only rev to 4000rpm whereas a petrol might rev to 7000 or maybe even 20,000 rpm. At 20,000rpm you need very little flywheel torque to generate a lot more power than a turbo diesel with loads of flywheel torque, but only 4000rpm...

I've driven a few of the same type of cars with different engines, for instance the BMW E92 325i and 335i, both automatics.The 335i has a huge amount of torque from 2.000 rpm, while the 325i needs more revs. I found the 335i the best for lazy driving, but fast. From any gear always lots of speed, while the 325i was much more fun to drive (although slower), but for normal commuting not as comfortable.

What you are describing there is one engine which has good low-medium rev range power (the 335i), I.e. At 50% revs it might make 60% of its peak power. compared to the second engine which has lower mid-range power. The flywheel torque that the first engine has may we'll be higher, but it is actually irrelevant to the experience you had.

Yes, if the two engines have exactly the same rev range you can compare the two engines easily using torque curves, but this is so often not the case that it's not really worth considering; comparing power curves (magnitude and shape) works in every instance.

[Just_a_fan]

Best power throughout the rev range is the same as best torque throughout out the rev range

Not if the two engines have different rev ranges... For example a Diesel engine, with lots of torque might only rev to 4000rpm whereas a petrol might rev to 7000 or maybe even 20,000 rpm. At 20,000rpm you need very little flywheel torque to generate a lot more power than a turbo diesel with loads of flywheel torque, but only 4000rpm...

Indeed so. I meant that if you had two engines with the same rev range, the one that has most torque at a given rev will automatically have the most power too. But such engines comparisons are rare for obvious reasons...

As with all things, you pick your engine to suit your usage. An engine that spends a lot of time commuting or towing, for example, will want to have peak power at a lower rev range than one that is to be driven fast / raced. Unless you like to sit on the highway at a steady 50mph with the engine screaming at 7000rpm as you drive to work, of course!

[machin]

Agreed.

[PlatinumZealot]

I will take the strongest engine.
My right foot will dictate how much torques reaches the wheels!

[Just_a_fan]

The gearbox has a big say in it too...

[Manoah2u]

The gearbox has a big say in it too...

+2.

I will take the strongest engine.
My right foot will dictate how much torques reaches the wheels!

actually, no, that's not at all how torque works. You'll be one of those people slamming the pedal to the metal when the road is slippery and icy and can't understand why you can't get up the hill or forward and choose to slam the pedal another feet further down the chassis thinking it'll get you moving.........

The left foot will dictate how much torque reaches the wheels when you're clutching away. That's why on a icy road uphill you choose to engage 2nd drive to pull away instead of 1st drive. Torque & Grip, and these 2 go hand in hand.

Torque is to get moving, power is to keep moving.

In all reality, most european cars genuinly lack torque and have too much horsepower. For normal commuter cars reaching speeds above 140 kph is completely useless, except for your occasional 'short stint' at the Autobahn. And that goes paired with a lot of braking, waiting, and speed limits too, so, really, why would one?

torque and acceleration are much more usefull and neccesarily. Sure, driving by yourself in a small commuter car to work doesn't take much. But then you get some passengers and you'll be screaming for salvation from the horror captain slow speeds.

Torque is what you want, power is additional. A gearbox indeed plays a good role in transferring torque & power to the wheels too.
I still swear by american engines, even though I have a Honda for commuting. I deliberately chose one with a higher torque figure and no, it's not a ricecracker.

[Silent Storm]

The gearbox has a big say in it too...

+2.

I will take the strongest engine.
My right foot will dictate how much torques reaches the wheels!

actually, no, that's not at all how torque works. You'll be one of those people slamming the pedal to the metal when the road is slippery and icy and can't understand why you can't get up the hill or forward and choose to slam the pedal another feet further down the chassis thinking it'll get you moving.........

The left foot will dictate how much torque reaches the wheels when you're clutching away. That's why on a icy road uphill you choose to engage 2nd drive to pull away instead of 1st drive. Torque & Grip, and these 2 go hand in hand.

Torque is to get moving, power is to keep moving.

In all reality, most european cars genuinly lack torque and have too much horsepower. For normal commuter cars reaching speeds above 140 kph is completely useless, except for your occasional 'short stint' at the Autobahn. And that goes paired with a lot of braking, waiting, and speed limits too, so, really, why would one?

torque and acceleration are much more usefull and neccesarily. Sure, driving by yourself in a small commuter car to work doesn't take much. But then you get some passengers and you'll be screaming for salvation from the horror captain slow speeds.

Torque is what you want, power is additional. A gearbox indeed plays a good role in transferring torque & power to the wheels too.
I still swear by american engines, even though I have a Honda for commuting. I deliberately chose one with a higher torque figure and no, it's not a ricecracker.

This!! You need Torque to get moving and in everyday driving you need better driveability.

Having a powerful engine will make no sense if it has weak bottom end or has less torque. It also depends on driving style, if you redline your engine in every gear or generally keep your engine at high RPM even when you are driving in city then torque won't matter to you. If you prefer to up shift early then you need torque.

So if PlatinumZealot likes to rev his engine to the redline then his choice to choose the strongest engine will suit him not someone who up shifts early.

[Manoah2u]

The gearbox has a big say in it too...

+2.

I will take the strongest engine.
My right foot will dictate how much torques reaches the wheels!

actually, no, that's not at all how torque works. You'll be one of those people slamming the pedal to the metal when the road is slippery and icy and can't understand why you can't get up the hill or forward and choose to slam the pedal another feet further down the chassis thinking it'll get you moving.........

The left foot will dictate how much torque reaches the wheels when you're clutching away. That's why on a icy road uphill you choose to engage 2nd drive to pull away instead of 1st drive. Torque & Grip, and these 2 go hand in hand.

Torque is to get moving, power is to keep moving.

In all reality, most european cars genuinly lack torque and have too much horsepower. For normal commuter cars reaching speeds above 140 kph is completely useless, except for your occasional 'short stint' at the Autobahn. And that goes paired with a lot of braking, waiting, and speed limits too, so, really, why would one?

torque and acceleration are much more usefull and neccesarily. Sure, driving by yourself in a small commuter car to work doesn't take much. But then you get some passengers and you'll be screaming for salvation from the horror captain slow speeds.

Torque is what you want, power is additional. A gearbox indeed plays a good role in transferring torque & power to the wheels too.
I still swear by american engines, even though I have a Honda for commuting. I deliberately chose one with a higher torque figure and no, it's not a ricecracker.

This!! You need Torque to get moving and in everyday driving you need better driveability.

Having a powerful engine will make no sense if it has weak bottom end or has less torque. It also depends on driving style, if you redline your engine in every gear or generally keep your engine at high RPM even when you are driving in city then torque won't matter to you. If you prefer to up shift early then you need torque.

So if PlatinumZealot likes to rev his engine to the redline then his choice to choose the strongest engine will suit him not someone who up shifts early.

If platinumzealot likes to rev his engine to the redline then he needs to do so because the car he's either driving a vehicle with an inadequate engine, or simply because he can't drive.

during commuting traffic you should not [ever] need to redline. It is fuel consuming, it wears on the engine and it's a neccesary compromise for having a engine that seriously lacks torque. you could say 'it lacks steam'.

it's not about driving stile, or liking to rev, it's about dealing with what is given. A car that needs to be revved high generally is a car that is lacking torque and needs to compensate by 'pulling' the engine to its limits to maintain motion.
Actually, this, in many cases, is also a sign that the engine is in a bad condition.

Redlining an engine on daily commute should never ever be neccesary, it only has potential use during 'racing', or to deal with other causes. In any case, high RPM is always bad for an engine if it is done for long periods of time.
It increases cilinder wear through higher friction and it thus uses up more oil. The generated heat causes various negative side-effects.

Running in low RPM, through torque, has several benefits. First of all, the engine gets less 'used' because it does not need to 'pull' itself to the desired speed through higher rate of combustion, but it uses the compression in lower rpm to 'smooth' itself forward.

A good example here is driving in heavy traffic jams. You can opt to keep it in 1st gear and rev up high then leave the pedal off and on, or you just set it in second gear and let it roll on the gearbox in 'idle' rpm. this causes much less engine wear = better.

You can also compare it with cycling. Cycling in a low gear whilst on a long straight, results in the need to spin your legs around quite a lot, so much, that it actually is tiresome and bad for the joints. Instead, putting it in 3rd gear, makes you use the power of pressure that your muscles provide to the pedals to forward the motion. It costs less effort and has lower wear on the body and joints.

somebody revving high through traffic is like somebody that goes jogging but instead of taking normal easy steps, passes the same distance moving their legs so fast as if they were jumproping towards their destination. It's abnormal, it's not neccesarily and generally a lack of understanding and skill of the activity.

I think we can all agree that somebody that's revving their engine tu the limiter to come out of the parking lot or through traffic doesn't control the clutch correctly nor understands how to drive.

the effect of torque vs power is most clear indeed in diesel engines, when you are accelarating, you notice in the lower revs a 'boost' and 'thrust' of power, while this 'thrust/boost' lowers the higher the revs go, essentialy feeling sluggish - untill you gear up and regain the boost/thrust.

Torque equals better driveability and better fuel consumption.

[Just_a_fan]

In all reality, most european cars genuinly lack torque and have too much horsepower.

My European engine has 470lbft at about 1900rpm. I think that is "adequate"

[Silent Storm]

actually, no, that's not at all how torque works. You'll be one of those people slamming the pedal to the metal when the road is slippery and icy and can't understand why you can't get up the hill or forward and choose to slam the pedal another feet further down the chassis thinking it'll get you moving.........

The left foot will dictate how much torque reaches the wheels when you're clutching away. That's why on a icy road uphill you choose to engage 2nd drive to pull away instead of 1st drive. Torque & Grip, and these 2 go hand in hand.

Torque is to get moving, power is to keep moving.

In all reality, most european cars genuinly lack torque and have too much horsepower. For normal commuter cars reaching speeds above 140 kph is completely useless, except for your occasional 'short stint' at the Autobahn. And that goes paired with a lot of braking, waiting, and speed limits too, so, really, why would one?

torque and acceleration are much more usefull and neccesarily. Sure, driving by yourself in a small commuter car to work doesn't take much. But then you get some passengers and you'll be screaming for salvation from the horror captain slow speeds.

Torque is what you want, power is additional. A gearbox indeed plays a good role in transferring torque & power to the wheels too.
I still swear by american engines, even though I have a Honda for commuting. I deliberately chose one with a higher torque figure and no, it's not a ricecracker.

This!! You need Torque to get moving and in everyday driving you need better driveability.

Having a powerful engine will make no sense if it has weak bottom end or has less torque. It also depends on driving style, if you redline your engine in every gear or generally keep your engine at high RPM even when you are driving in city then torque won't matter to you. If you prefer to up shift early then you need torque.

So if PlatinumZealot likes to rev his engine to the redline then his choice to choose the strongest engine will suit him not someone who up shifts early.

If platinumzealot likes to rev his engine to the redline then he needs to do so because the car he's either driving a vehicle with an inadequate engine, or simply because he can't drive.

during commuting traffic you should not [ever] need to redline. It is fuel consuming, it wears on the engine and it's a neccesary compromise for having a engine that seriously lacks torque. you could say 'it lacks steam'.

it's not about driving stile, or liking to rev, it's about dealing with what is given. A car that needs to be revved high generally is a car that is lacking torque and needs to compensate by 'pulling' the engine to its limits to maintain motion.
Actually, this, in many cases, is also a sign that the engine is in a bad condition.

Redlining an engine on daily commute should never ever be neccesary, it only has potential use during 'racing', or to deal with other causes. In any case, high RPM is always bad for an engine if it is done for long periods of time.
It increases cilinder wear through higher friction and it thus uses up more oil. The generated heat causes various negative side-effects.

Running in low RPM, through torque, has several benefits. First of all, the engine gets less 'used' because it does not need to 'pull' itself to the desired speed through higher rate of combustion, but it uses the compression in lower rpm to 'smooth' itself forward.

A good example here is driving in heavy traffic jams. You can opt to keep it in 1st gear and rev up high then leave the pedal off and on, or you just set it in second gear and let it roll on the gearbox in 'idle' rpm. this causes much less engine wear = better.

You can also compare it with cycling. Cycling in a low gear whilst on a long straight, results in the need to spin your legs around quite a lot, so much, that it actually is tiresome and bad for the joints. Instead, putting it in 3rd gear, makes you use the power of pressure that your muscles provide to the pedals to forward the motion. It costs less effort and has lower wear on the body and joints.

somebody revving high through traffic is like somebody that goes jogging but instead of taking normal easy steps, passes the same distance moving their legs so fast as if they were jumproping towards their destination. It's abnormal, it's not neccesarily and generally a lack of understanding and skill of the activity.

I think we can all agree that somebody that's revving their engine tu the limiter to come out of the parking lot or through traffic doesn't control the clutch correctly nor understands how to drive.

the effect of torque vs power is most clear indeed in diesel engines, when you are accelarating, you notice in the lower revs a 'boost' and 'thrust' of power, while this 'thrust/boost' lowers the higher the revs go, essentialy feeling sluggish - untill you gear up and regain the boost/thrust.

Torque equals better driveability and better fuel consumption.

100% agree with this but when I said reving the engine to redline I knew it's effects on engine life and fuel consumption but some engines are peaky and make useful power at top end of their powerband and need to be revved. Yes in day to day life higher torque is better as you can drive in higher gear and no need to floor the pedal.

Revving the engine does not necessarily mean that it lacks torque it could mean that the driver wants to accelerate faster. This does not apply to Diesel engines which have a narrow powerband in which up shifting to a higher gear as you said puts the engine in it's powerband where it regains boost.

When it comes to NA engines the higher you rev the faster you go as they make power at top end of the RPM and up shifting to higher gear will result in lower acceleration.

What I think is it depends on the engines characteristics. At times revving will give better acceleration in NA engine but not in turbo Diesel engine and up shifting will give better acceleration in Diesel as it regains boost at lower RPM.