torque vs. bhp.
Discussion
Torque can also be defined as the excess power available at any given speed divided by the mass of the vehicle. 
By excess power I mean the power available at that particular rpm minus the bhp needed to maintain that speed.
Therefore a light car with low torque could out perform a heavy car with bags of torque.
In short...
Torque can easily be defined but it's hard to explain! This could turn out to be the longest ever thread.
By excess power I mean the power available at that particular rpm minus the bhp needed to maintain that speed.
Therefore a light car with low torque could out perform a heavy car with bags of torque.
In short...
Torque can easily be defined but it's hard to explain! This could turn out to be the longest ever thread.
Alex said:
shpub said: All you need to know is
Torque wins prizes, BHP sells cars....
Carol Shelby IIRC
That'll be why all those F1 cars have such low revving torquey motors.
I'm no expert, but I think it is torque at the wheels (which is very dependant on gearing). F1 cars have very low gearing (due to 18000
rpm) which multiplies the engine torque. Honda vtec relies on the same thing. Someone with more knowledge of both techie and english
will be along soon to correct me! Sparks
If you want a race car, you want lots of power, high revs and a comparitively narrow power band.
If you want a road car (all be it a fast one), you want lots of torque and a wide power band.
Anyone who has tried to pull onto a busy roundabout with a race engine should know what I'm talking about!
Ian A.
If you want a road car (all be it a fast one), you want lots of torque and a wide power band.
Anyone who has tried to pull onto a busy roundabout with a race engine should know what I'm talking about!
Ian A.
Alex said:
shpub said: All you need to know is
Torque wins prizes, BHP sells cars....
Carol Shelby IIRC
That'll be why all those F1 cars have such low revving torquey motors.
Alex said: I think you're right. "Torque is good, but torque at high revs is better."
Torque at high revs is just more power...
I reckon the difference is over argued about, and just complicates matters.
Perhaps a simple example - a Griff 500 produces 250bhp from 5 litres, say at 5000rpm for simplicity. A 1500cc Radical has the same power, but at around 10,000rpm. Now, assuming both had flat torque curves to begin with, then if you put gearing that was exactly twice as low on the radical, then you would have identical acceleration, but the Radical would always be doing twice the revs.
Now, the 500 actually produces a lot of power low down, say 125bhp at 2500rpm, i.e. a nice fat torque curve. The radical doesn't really make any torque until high up, i.e. probably less than 70bhp at 5000rpm. Therefore you want to keep the revs up as high as possible to get any acceleration.
Given the choice on this basis, the 5.0 would clearly be the way to go! However, the Radical engine weighs around 80kg and is tiny, therefore it's worth the hassle of revving to keep it between 7000 and 9000 where it makes any decent power.
Hope that helps!
Imagine you are on a pushbike.
Torque is the muscle power in your leg that gets you up the hill and makes your thighs ache, bhp is when you are pedalling quickly on the straight bit and makes you go fast.
E.g. A steam engine has HUGE torque but low Bhp simply because it revolves at very low rpm. BHP is directly proportional to RPM.
That's pretty much all it is really!
Jas.
Torque is the muscle power in your leg that gets you up the hill and makes your thighs ache, bhp is when you are pedalling quickly on the straight bit and makes you go fast.
E.g. A steam engine has HUGE torque but low Bhp simply because it revolves at very low rpm. BHP is directly proportional to RPM.
That's pretty much all it is really!
Jas.
Torque at a given rpm measures the ability of the engine to exert force on the pistons from the resulting compbustion process. Due to MANY factors like valve lift/duration, intake/head dimensions cylinder design etc... an engine will operate optimally at a particular rpm (peak torque).
Above this torque falls away because insufficient air is getting into the cylinders as the inlet valves open for a shorter period with rising revs, the period during which te combustion can exert pressure on the pisotn shrinks and other parts of the engine may start to become a restriction preventing air flow scaling up with increased rpm.
I suppose also there's only so much air you can shove into a cylinder with each valve cycle, even with forced induction.
Above this torque falls away because insufficient air is getting into the cylinders as the inlet valves open for a shorter period with rising revs, the period during which te combustion can exert pressure on the pisotn shrinks and other parts of the engine may start to become a restriction preventing air flow scaling up with increased rpm.
I suppose also there's only so much air you can shove into a cylinder with each valve cycle, even with forced induction.
You'll find it at
www.bgideas.demon.co.uk/tmanual/tm01.htm
and
www.bgideas.demon.co.uk/tmanual/tm01.htm
As well as other ways of explaining the same thing.
J
www.bgideas.demon.co.uk/tmanual/tm01.htm
and
www.bgideas.demon.co.uk/tmanual/tm01.htm
As well as other ways of explaining the same thing.
J
mad dawg said: A bit late but here's my understanding:
torque (in lbs ft or Nm etc..) is a measure of an engines ability to do work
power (in hp or KW or whatever) is the rate at which it does the work.
simple as that!
so (assuming metric, probably wrongly!):
power is Nm/second
or not?!?
and what is PS? (besides a regional variation on BS!)
Power is the rate of doing work i.e. Power = Torque X RPM X Constant. Torque curves can be flat or peaky. To get more torque manufacturers make the torque more peaky but they have to give you a five or six speed box so that yoou can drive near your engines peak torque RPM. Ideally we need and infinitely variable gearbox so that regardless oof road speed we can always have peak torque available. Gas turbines failed because they have a substantial spool up time and it took an age to get though the gears. If you can keep your engine at or near peak torque RPM you will produce the most efficient system.
mikeylad said:
mad dawg said: A bit late but here's my understanding:
torque (in lbs ft or Nm etc..) is a measure of an engines ability to do work
power (in hp or KW or whatever) is the rate at which it does the work.
simple as that!
so (assuming metric, probably wrongly!):
power is Nm/second
or not?!?
and what is PS? (besides a regional variation on BS!)
Basically, yes.
the unit of power (in metric) is KW = KJ/S
Nm relates directly to KJ, but I'd have to get me old engineering textbooks out to remember how.
PS is German - short for Pferd Starke (literal spelling - my german is a bit shaky) which translates literally to horsepower. However 1PS does NOT equal 1HP (although its close), the german definition is slightly different. This is why I like metric!!!
cheers
Dave
Opps - my second link went wrong.
Look at www.pumaracing.co.uk/ for *everything* you would ever want to know...
To quote...
"One measure to be aware of though is the "continental horsepower" or PS. This stands for "PferdeStarke" - the German translation of "horse power". In France you sometimes see the same measure being called a "CV" for Cheval Vapeur. This measure was chosen in Europe as being the closest thing to a horsepower that could be expressed in nice round metric units - 75 kilogramme metres per second to be exact. It is commonly used by car manufacturers nowadays and tends to get used synonymously with bhp although it is actually a slightly smaller unit of power. One PS is about 98.6% of one bhp. The conversion table below covers the units most commonly used to express power and torque. Copyright David Baker and Puma Race Engines"
Look at www.pumaracing.co.uk/ for *everything* you would ever want to know...
To quote...
"One measure to be aware of though is the "continental horsepower" or PS. This stands for "PferdeStarke" - the German translation of "horse power". In France you sometimes see the same measure being called a "CV" for Cheval Vapeur. This measure was chosen in Europe as being the closest thing to a horsepower that could be expressed in nice round metric units - 75 kilogramme metres per second to be exact. It is commonly used by car manufacturers nowadays and tends to get used synonymously with bhp although it is actually a slightly smaller unit of power. One PS is about 98.6% of one bhp. The conversion table below covers the units most commonly used to express power and torque. Copyright David Baker and Puma Race Engines"
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