davep_96

A few questions regarding torque/HP:
1. I was wondering why peak torque and horsepower dont always happen at the same rpm.

2. why does peak torque happen at low rpms on some engines and higher rpms on others?

3.if the peak torque happens at say 1500rpm, why does the torque then start to decrease even though the horsepower increases? in other words, why does torque decrease with increasing engine speed after a certain point?

if torque= power X distance, i take it the "power" isnt refering to horsepower? so if this power is something besides horsepower, then what is the horsepower refering to? is HP the total OUTPUT power, while the "power" used for calculating torque is the INPUT power? I read the "how it works" site and im still having trouble putting this all together.

KENS_SS_4

Your question will take more then one whole book to fully explain. So here are some thoughts.

torque = ft * lbs

1 horsepower = 550ft * lbs / sec

Horse power is actual work. Torque is applied force.

It is basicly something like this: in dyno's there is a load that is being worked at a measured rate which yeilds a horsepower number. The applied force required to accelerate from one speed to the next is the calculated torque.

Gas engines are simple machines. They don't have linear operating outputs. Consider bore and stroke being equal. This is called square. Longer strokes and smaller bore or shorter strokes and larger bores are called over and under square. These are varied to make engines with the desired output.

davep_96

ok i guess i still dont get how HP and Torque are related besides the fact that you can find HP by torqueXrpm/5252. I get that torque is the amount of force applied in a circular motion, but i still dont see how HP figures into all this. if torque measures how much force we apply, then why do we need to know HP? To know how fast a car accelerates dont we just need to know how much force is being applied (torque)? I just dont really see exactly what HP represents/means to me when shopping for a car...

KENS_SS_4

What does horsepower mean when shopping for a car?
Ok try this.
Take a 4 x 8 sheet of plywood strap it to your front bumper and push on a bathroom scale attached to the rear bumper until you reach five mph.

Now when you first push the scale your feet are still and your arms and body are a rotational force around the axis of your feet (torque). The scale will read a lbs number. when you reach 5 mph the scale will show a steady number that will be the horsepower needed to push the plywood through the air (and all other friction).

Now go to 10 mph, 20 mph, and so on. The rolling friction is pretty light and pretty constant, but, the drag of the plywood is not. it is a cubed function. The faster you go the horse power needed to maintain that speed increases dramaticly. A wild guess would be 3000 hp to push that plywood to 150 mph.

So when shopping the drag coefficient and horsepower yield top speed potential. Torque and weight yield acceleration potential.

davep_96

Alright correct me if I'm wrong...

ok so a car with a good amount of torque will be able to accel fast because accel is governed by torque(as long as it doest weigh a lot and is geared right)?

And a car with a lot of HP will also be able to accel faster because HP measures how fast work can be done so its measuring how fast you can go through the gears?

liquidsmooth

iTrader: (1)

The way i'm reading it is torque will get you to a certain speed x faster with more torque, and hp is required to hold that speed, but i'm probably wrong -,-

Maybe an easier way to explain it and for us to understand would be to explain what would happen if you had 1 hp and 300 torque and visa versa.

johnh

iTrader: (1)

A couple of links that might help clear it up....

http://www.revsearch.com/dynamometer...orsepower.html
http://www.car-videos.net/articles/h...wer_torque.asp

nobird8991

iTrader: (4)

correct me if i'm wrong and this may not help a lot but it takes torque to make hp. tq is basically how fast you will accel. hp is how long you accel. so you will have a a strong amount of tq as long as you're still making power. without tq your hp will fade....

is that correct?

JohnnyC

If you want to be pinned back in your seat from a launch, you need torque.

If you want to be pinned back in your seat when you gun it and you are already going 100 MPH, you need horsepower.