Discussion
dannylt said: [quoteI have wondered on this topic before too. How could my Range Rover 3.5litre V8 (this is before I bought my Chimaera) have only 135bhp but my mates 2.0litre engine give 215bhp? Yet I know which would be quicker in an equal weight car.
Sorry, but unless it produces it's power in an extremely narrow band, the 215bhp engine should trounce the 135 one, given correct gearing. Or look at it another way, given correct gearing, the 215bhp engine can produce more torque at the wheels AT ANY SPEED compared to the 135 one (because it can use it's higher revs to translate the lower torque at a higher speed into higher torque at a lower speed). Of course, actual gearing will compromise this slightly, as will the width of the power bands from torque peak to power peak (the optimum gear change points).
It all depends on the engine torque. Assuming you put those two engines into the same car with the same weight, tires, transmission, rear-end, etc...
The car that would accelerate the quickest would be the one whose engine generated the most torque. If both engines generate the same peak torque then I suspect the win would go to the car whose peak was at the lowest RPM.
More horsepower!=more torque.
The real question is how much turning force the engine can apply to the wheels at any given instant in time.
Put another way, which car is faster to 60? The Cerbera Speed 6 or the 4.2? They both have virtually identical bhp figures do they not? But I'll bet the 4.2l V8 engine produces a lot more torque and at lower RPMs than the 4.0l I6.
JonGwynne said:
It all depends on the engine torque. Assuming you put those two engines into the same car with the same weight, tires, transmission, rear-end, etc...
The car that would accelerate the quickest would be the one whose engine generated the most torque. If both engines generate the same peak torque then I suspect the win would go to the car whose peak was at the lowest RPM.
More horsepower!=more torque.
The real question is how much turning force the engine can apply to the wheels at any given instant in time.
Put another way, which car is faster to 60? The Cerbera Speed 6 or the 4.2? They both have virtually identical bhp figures do they not? But I'll bet the 4.2l V8 engine produces a lot more torque and at lower RPMs than the 4.0l I6.
I'm not sure this is true. What I mean is some low bhp engines produce high torque but as they can't rev highly you don't get the benefits of gearing - as said below. Remember the torque at the wheels is a function of engine torque and gearing so being able to stay in a lower gear because you have a high revving engine will produce better acceleration. Why else would F1 engines rev so highly?
No it doesn't! It depends on the gearing too! Torque is really confusing things - just think about bhp versus revs. Gearing means you can use the bhp you want at any given speed.
Sorry, but unless it produces it's power in an extremely narrow band, the 215bhp engine should trounce the 135 one, given correct gearing. Or look at it another way, given correct gearing, the 215bhp engine can produce more torque at the wheels AT ANY SPEED compared to the 135 one (because it can use it's higher revs to translate the lower torque at a higher speed into higher torque at a lower speed). Of course, actual gearing will compromise this slightly, as will the width of the power bands from torque peak to power peak (the optimum gear change points).
It all depends on the engine torque. Assuming you put those two engines into the same car with the same weight, tires, transmission, rear-end, etc...
Nope. It's the one that generates more torque at the wheels. The high revving engine with no torque but lots of power will be using a nice low gear to generate more at-the-wheel torque, and will therefore beat the low power high flywheel torque engine
The car that would accelerate the quickest would be the one whose engine generated the most torque. If both engines generate the same peak torque then I suspect the win would go to the car whose peak was at the lowest RPM.
Better to talk about torque-at-the-wheels
More horsepower!=more torque.
Exactly
The real question is how much turning force the engine can apply to the wheels at any given instant in time.
Put another way, which car is faster to 60? The Cerbera Speed 6 or the 4.2? They both have virtually identical bhp figures do they not? But I'll bet the 4.2l V8 engine produces a lot more torque and at lower RPMs than the 4.0l I6.
It doesn't actually - the I6 is has a flatter torque curve, the V8 rises more sharply at 4k ish. It's the AREA under the torque curve that you're using WITH your gearing and road speed that counts.
Whoahhhh there.
Forget BHP, revs etc. Its torque you can feel when you plant your right welly into the shag-pile.
BHP is like god - worshipped by many but not actually real (waiting for the flack from that one ;-)
Yes, gearing matters but it's the torque at a given engine speed which makes you accelerate.
A car may produce 300BHP @ 10,000 RPM but this translates to only 157.56 lbs/ft of torque, whereas a V8 lump which produces 300BHP @ 5000RPM is chucking out a gut-squashing 315.12 lbs/ft of torque.
I know which I'd rather have under the bonnet (hence I drive a Chimp 450 NOT a banshee screamer like Honda S2000)
Forget BHP, revs etc. Its torque you can feel when you plant your right welly into the shag-pile.
BHP is like god - worshipped by many but not actually real (waiting for the flack from that one ;-)
Yes, gearing matters but it's the torque at a given engine speed which makes you accelerate.
A car may produce 300BHP @ 10,000 RPM but this translates to only 157.56 lbs/ft of torque, whereas a V8 lump which produces 300BHP @ 5000RPM is chucking out a gut-squashing 315.12 lbs/ft of torque.
I know which I'd rather have under the bonnet (hence I drive a Chimp 450 NOT a banshee screamer like Honda S2000)
At 5252 rpm torque equals bhp. The conversion of one to the other also uses this figure therefore bhp at 4000 rpm is divided by 4000 then multiplied by 5252 to give torque (if I have it the right way round). The torque at the wheels also depends on gearing as others have pointed out. Generally a flat torque curve will give better performance than a steep curve.
Over simplified:
Horsepower is the power which drives the car forward. Torque enables the car to pull. To clarify, a motorbike engined car can be extremely fast as it may have 200Bhp even though the torque could be as low as 70Ft/Lbs. The car is quite light and the engine does not need much torque in order to pull the car along.
A steam engine may have 5 Bhp, but may have 10,000Ft/Lbs of torque, purely because it turns at 25 revs/min.
Mathematically:
Power outputs or torque figures are often given individually for motors without reference to each other, here’s how to cross reference the figures.
Below is a mathematical formula to give a rough idea how much power an engine makes, if you don't have access to a dyno you can get a near perfect power figure by running a 1/4 mile and note the following.
Terminal speed squared, divided by elapsed time in seconds, times car weight (including driver) in pounds, divided by 1000, divided by 9.1 = power.
E.G. 2800LB car runs 14 second ET with a 100 mph terminal speed
100 X 100 = 10000 / 14 = 714.2 x 2.8 / 2000 / 9.1 = 220hp.
-------------------------------------------------------
Torque = (5252 x Horsepower) / RPM
Horsepower = (Torque x RPM) / 5252
The 5252 constant come from the following calculation below.
Torque = Work done per second / Radians per second rotation.
Therefore, 550 / 0.10472 = 5252
Where 1 revolution / second = 2 Pi Radians / 60 = 0.10472
Where Work done Horse Power = 33000 lb/foot Min or 550 lb/foot second.
Easy isn't it!
Jas.
Horsepower is the power which drives the car forward. Torque enables the car to pull. To clarify, a motorbike engined car can be extremely fast as it may have 200Bhp even though the torque could be as low as 70Ft/Lbs. The car is quite light and the engine does not need much torque in order to pull the car along.
A steam engine may have 5 Bhp, but may have 10,000Ft/Lbs of torque, purely because it turns at 25 revs/min.
Mathematically:
Power outputs or torque figures are often given individually for motors without reference to each other, here’s how to cross reference the figures.
Below is a mathematical formula to give a rough idea how much power an engine makes, if you don't have access to a dyno you can get a near perfect power figure by running a 1/4 mile and note the following.
Terminal speed squared, divided by elapsed time in seconds, times car weight (including driver) in pounds, divided by 1000, divided by 9.1 = power.
E.G. 2800LB car runs 14 second ET with a 100 mph terminal speed
100 X 100 = 10000 / 14 = 714.2 x 2.8 / 2000 / 9.1 = 220hp.
-------------------------------------------------------
Torque = (5252 x Horsepower) / RPM
Horsepower = (Torque x RPM) / 5252
The 5252 constant come from the following calculation below.
Torque = Work done per second / Radians per second rotation.
Therefore, 550 / 0.10472 = 5252
Where 1 revolution / second = 2 Pi Radians / 60 = 0.10472
Where Work done Horse Power = 33000 lb/foot Min or 550 lb/foot second.
Easy isn't it!
Jas.
GarryM said:
JonGwynne said:
It all depends on the engine torque. Assuming you put those two engines into the same car with the same weight, tires, transmission, rear-end, etc...
The car that would accelerate the quickest would be the one whose engine generated the most torque. If both engines generate the same peak torque then I suspect the win would go to the car whose peak was at the lowest RPM.
More horsepower!=more torque.
The real question is how much turning force the engine can apply to the wheels at any given instant in time.
Put another way, which car is faster to 60? The Cerbera Speed 6 or the 4.2? They both have virtually identical bhp figures do they not? But I'll bet the 4.2l V8 engine produces a lot more torque and at lower RPMs than the 4.0l I6.
I'm not sure this is true. What I mean is some low bhp engines produce high torque but as they can't rev highly you don't get the benefits of gearing - as said below. Remember the torque at the wheels is a function of engine torque and gearing so being able to stay in a lower gear because you have a high revving engine will produce better acceleration. Why else would F1 engines rev so highly?
The "benefit of gearing" is to allow forward motion using the least amount of torque possible.
Anyone who's ever ridden a multi-gear bicycle knows that the lower the gear, the easier it is to pedal. There's two ways to look at this: if you shift to a lower gear you can either produce the same acceleration from less torque or you can apply the same torque as you were before and get faster acceleration.
Ergo, in two cars car with the same transmission, rear end and weight, the one with the torquier engine will deliver faster acceleration.
Your argument about the ability to stay in lower gears longer with higher revving engines is valid in theory and would certainly apply to F1 cars that rev to something insane like 20,000 rpm. But in road cars, the difference between a redline at 6000rpm and one at 7000 isn't going to make a great deal of difference.
I have a Honda S2000 that makes 240bhp (not much less than the first 4.0 liter Chims and Griffs produced) but I bet either one of those cars would spank the Honda badly in a 0-60 test and far worse in a 0-100.
JonGwynne, first let me say that to a point I agree with all you say - I own a Griff 500 which slams the "torque is best" dogma home every time I drive it! 
The bit I don’t agree with in your previous post is when you say:
"The car that would accelerate the quickest would be the one whose engine generated the most torque. If both engines generate the same peak torque then I suspect the win would go to the car whose peak was at the lowest RPM"
It is in this situation that gearing would enable the car with peak torque produced at a higher rpm to accelerate faster - like the bicycle analogy.
It is an interesting subject though (am I sad? - don't answer that!) and one which I don’t pretend to fully understand. I agree that when taken to extremes, like traction engines/water wheels with huge amounts of torque and low bhp on the one hand and bike/F1 engines with low torque and high bhp on the other, the theory seems simple. I can also see that if the power figures are not too dissimilar but one produces it at say 20% higher revs than the other, I would go with the lower revving engine, i.e. the one with more torque. Where it gets difficult to understand (for me at least!) is when the power of a peaky engine is higher but not dramatically so.
The bit I don’t agree with in your previous post is when you say: "The car that would accelerate the quickest would be the one whose engine generated the most torque. If both engines generate the same peak torque then I suspect the win would go to the car whose peak was at the lowest RPM"
It is in this situation that gearing would enable the car with peak torque produced at a higher rpm to accelerate faster - like the bicycle analogy.
It is an interesting subject though (am I sad? - don't answer that!) and one which I don’t pretend to fully understand. I agree that when taken to extremes, like traction engines/water wheels with huge amounts of torque and low bhp on the one hand and bike/F1 engines with low torque and high bhp on the other, the theory seems simple. I can also see that if the power figures are not too dissimilar but one produces it at say 20% higher revs than the other, I would go with the lower revving engine, i.e. the one with more torque. Where it gets difficult to understand (for me at least!) is when the power of a peaky engine is higher but not dramatically so.
It's amazing how easy this becomes after a simple demonstration, try www.howstuffworks.com it's an invaluable font of information.
Paceracing said
Mathematically:
Below is a mathematical formula to give a rough idea how much power an engine makes, if you don't have access to a dyno you can get a near perfect power figure by running a 1/4 mile and note the following.
Terminal speed squared, divided by elapsed time in seconds, times car weight (including driver) in pounds, divided by 1000, divided by 9.1 = power.
Jas.
I assumed this was power at the wheels which (in my view) is the only real measure of performance other than timing the car!
Never seen this calculation before and whilst I think "near perfect" is stretching the truth a bit its actually proved a good rough guide for the cars I did the calcs on.
one trend I did get was lighter cars calculate at lower than actual power but heavier cars start to go the other way.
My cossie gained 40Bhp using this calc when I upgraded the suspension and improved the quarter performance without a change in power!
plipton said: Whoahhhh there.
Forget BHP, revs etc. Its torque you can feel when you plant your right welly into the shag-pile.
BHP is like god - worshipped by many but not actually real (waiting for the flack from that one ;-)
Yes, gearing matters but it's the torque at a given engine speed which makes you accelerate.
A car may produce 300BHP @ 10,000 RPM but this translates to only 157.56 lbs/ft of torque, whereas a V8 lump which produces 300BHP @ 5000RPM is chucking out a gut-squashing 315.12 lbs/ft of torque.
I know which I'd rather have under the bonnet (hence I drive a Chimp 450 NOT a banshee screamer like Honda S2000)
No no no no no - this demonstrates how you've got it perfectly wrong. If the revvy car in your example had gearing exactly twice as low, then the actual torque at the wheels, i.e. the acceleration will be IDENTICAL, assuming the torque profiles are the same, i.e. the revvy one is half the torque at double the revs.
Torque is IRRELEVANT. Torque at a particular revs may be interesting, but actual acceleration felt also depends on the gearing. Now, the PROFILE of the torque may be interesting too, but never a raw torque number.
>> Edited by dannylt on Thursday 31st October 18:11
incorrigible said: Just a clarification, but the Rover V8 in a Range rover produces either 185 or 195 bhp depending on which model you've got
Not if you've got an early one like mine.
Early 1970s Range Rovers had the 3.5litre with twin Strombergs, i.e no fuel injection and produced 135bhp. See owners handbook or James Taylor's books Matt
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"No no no no no - this demonstrates how you've got it perfectly wrong. If the revvy car in your example had gearing exactly twice as low, then the actual torque at the wheels, i.e. the acceleration will be IDENTICAL, assuming the torque profiles are the same, i.e. the revvy one is half the torque at double the revs."
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Stay calm, it's only a debate here....
Yes, I agree. But what you seem to be overlooking is that if you are pulling away from a standstill, the engines cannot instantly be running at their perfect rpm (assuming a normal number of gears and not infintely variable or something silly). So the 'revvy' engine will be forced to run at a lower rpm and will thus struggle to reach its ideal rpm because it hasn't got a lot of TORQUE at low revs. Whereas the torquey engine will be accelerating an identical car much more quickly already. That is unless I'm overlooking the fact that you are some amazingly clever driver who can slip the clutch in any gear to keep that optimum rpm. But then I guess you'd be wasting a lot of your power as 'hot air'! he he
If you increased the weight of an F1 car to something near a Chimaera, do you think that the F1 'revvy' engine would still out accelerate the Chimaera. I think it wouldn't even have enough TORQUE to reach it's ideal rpm and probably wouldn't even be able to start off.
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"Torque is IRRELEVANT. Torque at a particular revs may be interesting, but actual acceleration felt also depends on the gearing. Now, the PROFILE of the torque may be interesting too, but never a raw torque number."
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Well I think 'irrelevant' is a bit harsh! We are all of course assuming normal/usual ratios etc for gearing here when we discuss matter.
Matt
>> Edited by taylormj4 on Friday 1st November 00:06
>> Edited by taylormj4 on Friday 1st November 00:07
"No no no no no - this demonstrates how you've got it perfectly wrong. If the revvy car in your example had gearing exactly twice as low, then the actual torque at the wheels, i.e. the acceleration will be IDENTICAL, assuming the torque profiles are the same, i.e. the revvy one is half the torque at double the revs."
------------
Stay calm, it's only a debate here....
Yes, I agree. But what you seem to be overlooking is that if you are pulling away from a standstill, the engines cannot instantly be running at their perfect rpm (assuming a normal number of gears and not infintely variable or something silly). So the 'revvy' engine will be forced to run at a lower rpm and will thus struggle to reach its ideal rpm because it hasn't got a lot of TORQUE at low revs. Whereas the torquey engine will be accelerating an identical car much more quickly already. That is unless I'm overlooking the fact that you are some amazingly clever driver who can slip the clutch in any gear to keep that optimum rpm. But then I guess you'd be wasting a lot of your power as 'hot air'! he he
If you increased the weight of an F1 car to something near a Chimaera, do you think that the F1 'revvy' engine would still out accelerate the Chimaera. I think it wouldn't even have enough TORQUE to reach it's ideal rpm and probably wouldn't even be able to start off.
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"Torque is IRRELEVANT. Torque at a particular revs may be interesting, but actual acceleration felt also depends on the gearing. Now, the PROFILE of the torque may be interesting too, but never a raw torque number."
--------------
Well I think 'irrelevant' is a bit harsh! We are all of course assuming normal/usual ratios etc for gearing here when we discuss matter.
Matt
>> Edited by taylormj4 on Friday 1st November 00:06
>> Edited by taylormj4 on Friday 1st November 00:07
This debate keeps coming up... should just post that link to that comparison between a water wheel and a combustion engine, and shut up, but I couldn't find it.
Anyway, I agree with you entirely. Except that if you dump the clutch on a Chimaera at peak torque it will just spin the wheels anyway. I'm sure something like the S2000 still has peak torque around 5 or 6k, so that seems an appropriate point to drop the clutch too.
Certainly once you're moving, and assuming you have effective gearing for the powerband (torque peak to power peak), then it IS power that counts. And 210 bhp will make a big difference over 135.
Maybe irrelevant is a bit harsh, but certainly engines which are very "peaky" will have appropriate gearing, e.g. motorbikes with low gearing and very close ratios.
>> Edited by dannylt on Friday 1st November 10:16
Anyway, I agree with you entirely. Except that if you dump the clutch on a Chimaera at peak torque it will just spin the wheels anyway
. I'm sure something like the S2000 still has peak torque around 5 or 6k, so that seems an appropriate point to drop the clutch too. Certainly once you're moving, and assuming you have effective gearing for the powerband (torque peak to power peak), then it IS power that counts. And 210 bhp will make a big difference over 135.
Maybe irrelevant is a bit harsh, but certainly engines which are very "peaky" will have appropriate gearing, e.g. motorbikes with low gearing and very close ratios.
>> Edited by dannylt on Friday 1st November 10:16
As this (great) debate admirably demonstrates, there are many more factors to rapid acceleration than simply power and torque: gearing and the ability to transmit the power to the road (traction) have a huge part to play.
So its either everyone outside to practice side-stepping the clutch at 6000rpm, or inside to design the perfect 4WD with CVT.
>> Edited by jeremyc on Friday 1st November 10:02
So its either everyone outside to practice side-stepping the clutch at 6000rpm, or inside to design the perfect 4WD with CVT.
>> Edited by jeremyc on Friday 1st November 10:02
dannylt said: This debate keeps coming up... should just post that link to that comparison between a water wheel and a combustion engine, and shut up, but I couldn't find it.
Anyway, I agree with you entirely. Except that if you dump the clutch on a Chimaera at peak torque it will just spin the wheels anyway
Certainly once you're moving, and assuming you have effective gearing for the powerband (torque peak to power peak), then it IS power that counts. And 210 bhp will make a big difference over 135.
Maybe irrelevant is a bit harsh, but certainly engines which are very "peaky" will have appropriate gearing, e.g. motorbikes with low gearing and very close ratios.
>> Edited by dannylt on Friday 1st November 10:16
Actually, if I remember my sales literature correctly, the S2000's torque peak is at 8900 RPM. ;->
Come on Guy's we all know that its the shape of the Torque/power curve thats important, keep the torque curve flap and the power will keep climbing with the revs.
Big engines usually produce loads down low but tail out earlier....But smaller usually can't produce as much torque so have to rev much higher to make the power.
It's preference were you want it high up the rev range or low down.
If only we could develope an engine with 100lft torque from 1000rpm to 18000rpm, I'd put my name down for one!
PS I have the 6.3litre 7000Rpm V8 and a 2.0 litre turbo nutter and I like to rev em!
Big engines usually produce loads down low but tail out earlier....But smaller usually can't produce as much torque so have to rev much higher to make the power.
It's preference were you want it high up the rev range or low down.
If only we could develope an engine with 100lft torque from 1000rpm to 18000rpm, I'd put my name down for one!
PS I have the 6.3litre 7000Rpm V8 and a 2.0 litre turbo nutter and I like to rev em!
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