[duncan]

specific power output is as far as my understanding goes bhp to displacement... it is actually to measure break horse power to cc u know.
like measuring a 4.5 litre engine to a 3.0 litre engine is either a bold claim of the small engine or is proving how underpowered the bigger engine is therefore you use bhp/litre...the calculation is somewhat like per 100 tonnes you reqire 50 bhp to move the object
but power output/ specific power is not as important just the knowledge of the weight power and torque is more important

[amitabh_kaushal]

Hi, i have few questions -

Higher torque at lower rpm is good for city driving but on highways ?
Higher torque at lower rpm does affect fuel economy ?

which car is good higher torque at lower rpm or higher torque at higher rpm.

[santosh.s]

Originally Posted by duncan

specific power output is as far as my understanding goes bhp to displacement... it is actually to measure break horse power to cc u know.

the moment I saw "per-litre", I thought it must be referring to the litre of ever inflating (pricewise) petrol, and it didn't make any sense

yes, it shouldn't be important then... higher rating will only mean more stress on the engine!

[tsk1979]

higher torque at low rpm means good drivability in city and medium highway performance
for example you are doing 30kmph in third gear with the engine doing 2000rpm. If your peak torque is developed at 1800-2200rpm this means you can drop down by 5-10kmph and then accelerate again. But if your peak torque is developed at 3500rpm, the moment you go down to 20, you may need to shift to second gear.
Same is true if you are in 5th gear at 70kmph on the highway with engine at 1800rpm or so. If your peak torque is around that range you can perform overtaking without shifting down to 4th. The most comfortable rpm for overtaking is one at which peak torque is produced.

[sbasak]

In electric motors, the torque is more or less constant at any RPM. Better the engine, it will keep highest torque available for higher range. Some very good diesel engines (Mercedes etc.) keep highest torque almost constant between 1800-4000 RPM range. Constant torque at wider RPM range means you need to change gears less frequently and good performance of the car. The acceleration and traction of the car depends on torque - power only affects max speed you can achive with the vehicle.

[santosh.s]

Originally Posted by sbasak

The acceleration and traction of the car depends on torque - power only affects max speed you can achive with the vehicle.

just to elaborate: with proper gearing, traction and speed from engine (read torque and rpm) can be compromised for each other. to give a practical example, tractors have power ratings around 50bhp (close to small cars), trucks (in india!) are generally around 150bhp whereas 100bhp is resonably powered car as per our standards. Now you can make out the difference- tractors can pull a plough through hard ground but at dead slow speeds, trucks can be laden with 10-15 tonne of pay load but will travel below 60 kmph I guess, whereas 50bhp car with around 1 tonne gross weight will touch 100kmph within 20 seconds or so... and a 100bhp car will take just about 10 seconds to reach 100kmph mark... its the net effect of engine and gearing that matters for what is delivered at wheels.

also torque and power responses (wrt rpm) are two sides of a coin, if you have one of them you already have the other! The confusion arises because peak values of each are generally specified, not the curves themselves. torque peak is bound to happen at lower rpm as compared to where the power peak occurs (because power is proportional to the product of torque and RPM ITSELF)

hope this helps

[sbasak]

Power = Force x Velocity
So, if you reduce velocity, you have more force ( = pull higher load)

Gear box basically acts like torque multiplier.

Volvo trucks have power in the range of 200-500 HP and 9-13 gears.

[Shan2nu]

Just having a high peak torque at a given rpm is of no use. Your torque curve is what matters.

A car with a meaty torque curve throughout the revv band will perform better than another car with just one everest of a peak at a given rpm and nothing before or after it.

Shan2nu

[santosh.s]

Originally Posted by amitabh_kaushal

Hi, i have few questions -

Higher torque at lower rpm is good for city driving but on highways ? \

hope you have got enough explaination, haven't you?

which car is good higher torque at lower rpm or higher torque at higher rpm.

Car with good lowend torque which I know of are maruti's baleno, wagonr. additionally they have overall flat curve across the whole range. Swift is also supposed to have good lowend torque, which has retuned (don't know how much) esteem engine.

ikon (1.6 rocam) is well known for its incredible lowend response and santro-erlx has much better lowend as compared what it had earlier.

honda city vtec should be great at both low and high rpms, and also much more happy to rev in high band than others. because this is the essence of vtec technology, unless my memory is betraying

curious to get fiesta updates....

Higher torque at lower rpm does affect fuel economy ?

engines are supposed to deliver their best at rpms from the peak torqe to peak power, and also to be efficient. As I had mentioned earlier, efficiency generally keeps getting worser as egngine speeds up, so I don't think engines with good lowend response tend to be less on mileage. it might be the otherway around.... consider the fact that all the cars I have mentioned are on better side in terms of FE (in so called "its class"), except ikon...

[sreenivass]

Originally Posted by sbasak

In electric motors, the torque is more or less constant at any RPM. Better the engine, it will keep highest torque available for higher range. Some very good diesel engines (Mercedes etc.) keep highest torque almost constant between 1800-4000 RPM range. Constant torque at wider RPM range means you need to change gears less frequently and good performance of the car. The acceleration and traction of the car depends on torque - power only affects max speed you can achive with the vehicle.

There are two kinds of electric motors aren't they: series and shunt. Shunt motor can give good RPM with lesser torque ans series motor provides a great initial torque. That is why Both kinds of motors are used in electric locomotives, series for starting and shunt to maintain momentum and pick up speed.