engine size and travel distance

vixmony

thanks guys for your every input.

thescouselander

cyclonebri1 - I think you should read the bottom of your explanation re the case for horse power. I can assure you - you absolutely do feel the physics.


If you knew the torque at the wheel you could directly translate that into acceleration. The reason you have to consider power over torque is because the gearing between the engine and the wheels alters the torque available to accelerate the car forward. As in the example at the bottom you can have a shed load of torque but hardly any power so you wont be going any where fast.

"It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*.

Low torque at high RPM (and high power) can be turned into high torque at the driving wheels by gearing. High torque at low RMP - not so good because the gearing means the torque at the wheels is reduced:

Oops. Now we see the rest of the story. While it's clearly true that the water wheel can exert a *bunch* of force, its *power* (ability to do work over time) is severely limited.

The reason the car has accelerated is because the engine has done work give the car more kinetic energy. If we work out how much work the engine has done over a period then you can work out how much energy has been put into the car and ignore the affect of gearing. So if you look at the area under the graph of the power curve you can see how much work has been done and thus how much the car has accelerated.

You can demonstrate this to yourself in a car that has a relatively flat torque curve. Lets suppose such a car has a completely flat torque curve between 2000 rpm and 4000 rpm.

For a given road speed you can select a number of different gears -

In a lower gear you might be at 3500 rpm but in a higher gear you might be at 2000 rpm. In both instances the engine is producing exactly the same torque but when you floor the accelerator you will obviously accelerate harder in the lower gear - this is because the engine is producing more power in the lower gear (at higher RPM) even though the torque from the engine is the same as in the higher gear.

cyclonebri1

thescouselander wrote: »

cyclonebri1 - I think you should read the bottom of your explanation re the case for horse power. I can assure you - you absolutely do feel the physics.


If you knew the torque at the wheel you could directly translate that into acceleration. The reason you have to consider power over torque is because the gearing between the engine and the wheels alters the torque available to accelerate the car forward. As in the example at the bottom you can have a shed load of torque but hardly any power so you wont be going any where fast.



Low torque at high RPM (and high power) can be turned into high torque at the driving wheels by gearing. High torque at low RMP - not so good because the gearing means the torque at the wheels is reduced:




The reason the car has accelerated is because the engine has done work give the car more kinetic energy. If we work out how much work the engine has done over a period then you can work out how much energy has been put into the car and ignore the affect of gearing. So if you look at the area under the graph of the power curve you can see how much work has been done and thus how much the car has accelerated.

You can demonstrate this to yourself in a car that has a relatively flat torque curve. Lets suppose such a car has a completely flat torque curve between 2000 rpm and 4000 rpm.

For a given road speed you can select a number of different gears -

In a lower gear you might be at 3500 rpm but in a higher gear you might be at 2000 rpm. In both instances the engine is producing exactly the same torque but when you floor the accelerator you will obviously accelerate harder in the lower gear - this is because the engine is producing more power in the lower gear (at higher RPM) even though the torque from the engine is the same as in the higher gear.

Nope, you lose, sorry

You still need torque to get off tickover regardless of gearing, it's easy,torque comes in 1st, bhp takes over, not even catch 22, as you don'[t get the latter without the former,