If you have it figured out then lets hear it. This is certainly a good read Al. Seeing as I'm not the calc grad I'd be interested to hear the break down.

 

This is a good discussion. I have always had an idea that torque was actual get up and go, and the hp was more of a top end thing. I guess it really depends on the set up, but on average i think thats how it is, im glad this thread was made, helpin me learn more, again

 

There's a saying ..... "Torque wins races, horsepower sells cars."

 

F1 cars are 3.0L. none of them are even remotely as small as 1.8L and haven't been since 1989

and in the 80s they were 3.0L if N/A and 1.5L if turbo (most were turbo), but these engines "only" spun about 13k-15k rpm (compared to the 19k of today's F1 engines).

but still, F1 cars only weigh 1320 lbs with driver and fuel. they don't NEED to be torque monsters.



my viewpoint on torque vs hp is this:

just enough torque to move the car is enough torque. more torque and the car gets exponentially more difficult to drive fast/smoothly.


also, the shape of the torque/hp curves is VERY dependent on what you are doing with the car, ie towing/street car/drag racing/road racing/autocross/etc.

 

horsepower is how fast you hit the wall

torque is how far you take it with you

 

bingo. usable power = area under curve IN USABLE REV RANGE (ie, where you spend most of your time. this is a mathematical concept called "integration" (calculus)

whether you are talking about the torque or hp curves does not matter, as they are linked and proportional anyway (in otherwords, increasing the area under the torque curve increases the area under the hp curve by the same amount).

 

Give me a tall, flat torque curve and a wide rpm range. You can have the hp for dyno racing.

 

[engineer]Torque is a function of volumetric efficiency. VE is the ratio of air that you can supply the volume of a cylinder compared to an equal volume outside the combustion chamber. Supply more air and fuel to a cylinder and you will raise the cylinder pressure. Forced induction does this nicely. If I had a scanner, I could post a free body diagram of the forces involved, with the pressure acting on the area of the piston creating a force that travels through the con rod into the cranks radius and voila, torque. Peak Torque is reached at peak VE.

Now, obviously most engine's do not reach their peak HP/TQ numbers at the same RPM. HP is defined as work done over time. You may notice that the units for work are the same as the units for torque, force times a distance. A 4-stroke engine has half as many power strokes as complete turns. At low RPM (remember tq*RPM is HP too), we have fewer chances to achieve that high cylinder pressure per unit time, lets say 1 second, and because engines do not typically reach their highest VE low in the power band, HP numbers are low.

As RPM's are raised, more and more power strokes occur per this same second, and power loads are a function of the average cylinder pressure, not just peak. Peak HP can often be found therefore after the peak TQ number is reached.

As far as gearing is concerned, you may notice that you can half the speed of any shaft, and under the same input conditions double the torque. The HP figure however, will remain unchanged. Another free-body diagram would show this nicely. As an engine revs several times through the power band over its pass down a 1/4 mile, peak acceleration is found when the TQ numbers are highest (without accounting for traction, aero drag).[/engineer]

 

Wussy! Having an excessive amount of torque in the low band is what makes a car/bike fun. You just never know what's going to happen when you stomp that pedal or twist that grip.

Having an excessive amount of torque in the low band is also necessary when you have a 4500lb Cadillac. Powerband from 500rpm to 3500rpm kicks ass! 2.14 ring gear and 0.68 overdrive inna house!

 

+1