Horsepower and Torque. Silly question...

[Shurup]

OK, everybody knows that more HP is better (cooler

), but I think I need some definitions and examples in this question. What stands for what? What are the differences comparing 150 HP 300 lb.ft. car and 300 HP 150 lb.ft. car? What shoud I expect from each of them? Thx.

 

[Shurup]

My girlfriend got a job at Olds Chev dilership and she asked me that question and I couldn't answer. Shame on me.

 

[rkj082000]

Check out www.howstuffworks.com and do a search on Horsepower or torque, they have alot of info. on both topics.

 

[Hokie]

1 HP = 550 lbf * ft/s

HP = power and torque is a moment (Sorry... I am an engineering student)

Here's the simple rule of thumb...

Torque gets you off the line, HP allows you to pass on the highway. Low end and mid range torque is what makes a car feel strong towing and driving around town... More torque, less need to downshift.

 

[Alec]

Yup. Trucks, musclecars, and heavier vehicles in general tend to have more tq than hp because tq is what moves all that weight off the line. Smaller cars tend to have more hp, which is why many racers want to race from a "roll-on" and not off the line. Given an engine with equal tq and hp, it is usually easier to improve hp with bolt-ons and power adders than improving tq.

 

[Shurup]

OK, I think I got the point.
TQ - how hard the evgine can pull
HP - how fast the engine can accelerate the car

Is that right?

 

[Nate1]

Think of it this way. If you are going slow and want to get going fast (espically if you are heavy) the more torque, the quicker its going to happen...
If you are already going (relatively) fast and want to go faster, the more hp you've got, the quicker you're gonna get going faster.

 

[C5 Pewter Coupe]

Also figure that HP is basically torque multiplied over time.. and that you can convert high hp/low torque engine into lower hp/higher torque at the wheels with gearing..

 

[Scormunch]

My favorite quote... and somewhat appropriate in this thread:

"Horsepower is how fast you hit the wall... Torque is how far you drag it"

 

[dogfriend]

Elaborating on HokieBerts reply:

Torque is the twisting force or moment applied at the center of the crankshaft (for an engine). A moment is equivalent to two parallel forces acting in opposite directions. The units of torque are lbs*ft or N*m. A torque of 1 lb ft is equivalent to a 1 lb force applied at a distance of 1 foot from the center of rotation.

Horsepower (HP) is a measurement of work per unit time; in other words, how much work is performed per second (or minute or hour).

Work in turn is defined as Force x Distance. So HP = (Force x Distance) / Time.

Substitute Torque = Force x Distance , or Force = Torque / Distance

HP = (torque x distance) / (distance x time)

or

HP = (A) x (torque / time) where (A) is a constant

Using lbs for force , feet for distance, and seconds for time, the constant ends up as 550, so

One HP = 550( lb * ft)/sec

Note: This is a dimensional analysis, no flames from the math majors needed or wanted

So, horsepower can be thought of as the ability for your engine to provide torque (or twisting of the crankshaft) in a certain amount of time.

If your engine is a small four cylinder, it won't have a high torque rating but sense it can rev pretty high, the horsepower will be higher than the torque. (e.g. 110hp, 87 ft lbs)

If you have an large truck engine, it will have monster torque, but can not rev very high without blowing apart, so the horsepower will be lower than the torque. (330hp, 850 ft lbs)

 

[Shurup]

That was very helpfull . Thanks dogfriend.

 

[Rydin Dirtay]

lol scor m