Ryals

iTrader: (1)

I always hear about HP and torque. Is HP what determines how fast your car can take off from a stop and get to high speeds. Also what does torque mean or do? Always been curious, never really knew for sure.

Wurf

Torque is actually what accelerates your car. It's the measure of twisting force of your engine. More torque is good up until the point your tires can't put it to the road anymore.
HP is simply torque measured over time.

Ryals

iTrader: (1)

So the two are directly related? I you have more HP you more Torque?

Dohcser

Torque actually is what does the work, HP is how fast will it do the work. So when people get caught up on HP (honduh) is only because of ignorance.

Ryals

iTrader: (1)

So why is HP always the topic of conversation, why don't you ever hear anyone mention anything about increasing their torque instead of HP?
So the more torque the better to a limit?

Jime

iTrader: (10)

Now, it's important to understand that what we actually measure (on a dynomometer) is torque, expressed in foot pounds (in the U.S.), and then we *calculate* actual horsepower by converting the twisting force of torque into the work units of horsepower.

mjg

Horsepower is a more general terminology, At a given time, or part of the power curve? (Is this right). At any given point in horsepower curve, you have a certain amount of torque. It's the area under the curve, that should be torque right (Integrate??)

Stephen Max

iTrader: (59)

Just a few things to consider.

In a rotating machine, torque and hp are not independent. They are related to each other by engine rotational speed. So you can talk about either torque or horsepower, take your pick. It is not possible to raise torque at a particular rpm without also raising hp at that rpm. It is possible to raise peak torque without raising peak power, and vice-versa. People talk about torque when they really mean low-end power, though.

The quantity required to change a vehicles kinetic energy over a time interval is power, not torque. Power implies motion, torque does not. You can apply torque to a stationary shaft and no power will be involved if the shaft does not move. Power comes into play when you are applying a torque to a rotating shaft.

Consider pushing against something with a 50 lb force, like a parked car. Now think about applying a 50 lb force to a car that is moving away from you at 10 mph. It is harder to do that because it requires power, not just force. What about applying 50 lb to a car that is moving at 20 mph? If you are like most people, you wouldn't be able to generate that much power, even though anybody could apply 50 lbs to a stationary object.

Furthermore, it is power that is the measure of merit when it comes to determing the efficiency of an engine. An engine converts chemical energy in the gasoline to work over a time interval. Work is defined as a force applied over a rotational distance as the engine turns, and the rate of work is power.

Tuner's like to work with the torque curve because it is flat and you can detect increases in torque easier than increases in power, especially at low-mid rpm.

Wurf

Stephen has the physics class answer and he is correct.

Sorry this is so long, but....

In regards to what it feels like to have one type of motor over another - as in a motor with lots of low end torque and less top end vs a motor with more top end instead of low end, the former is more satisfying to drive on the street while the later can be faster on the track. There are few absolutes however.

Take a naturally apirated high winding 2.0 liter four cylinder and optimize it's induction, heads, cam, rotating assembly, and exhaust to make max power at 8500rpm and let's say it makes 200hp - without even mentioning torque. It will typically have a large port, short runner intake, big valve, big port heads, and big exhaust ports and tubing. Max torque will be way up there in the 5000rpm range.

Stick it in a 3500lb Maxima with stock gearing and test drive it with a five speed. It will be a DOG out of the hole and won't come alive until you are spinning the bejeezus out of it. Once you get it wound up, it's lots of fun. Otherwise it's a pain the but to drive, and it will get old in a hurry.

Take that same motor and change the induction to a longer runner style with small crossectional area intake, run a shorter duration camshaft for more low end torque, run smaller port, high flowing heads, smaller port headers, and lets say it makes max power at 6200 rpm of around 160hp, but it makes another 45ft lbs ft of torque at say 3500rpm. It wouldl be MUCH nicer to drive, much more responsive off the line, and you won't have to dog whip it to get moving all the time. You trade max high end HP for low end torque.

Now take that same Maxima and stick a 3.5L motor in it with 250hp and another....oh I don't know......100ft lbs of torque. You will feel that under your right foot. Torque steer and traction control switch anyone?

Like others have mentioned here before, it's the total package that counts. The right gearing with the right motor combo for the weight of the car etc. It all makes a difference. The old saying, there is no replacement for displacement is quite accurate.

Why spin the crap out of a dinky four banger when you can take it easy on a motor with almost twice the displacement, and better breathing?

You can build a little bee stinger 4cyl and spin the hell out of it, but depending on what you install the thing in, you might need more gear to get it into that powerband sooner. You can make up for the loss of low end torque with more torque multiplication through gearing - drop some lower gears ( numerically higher ) in the differential.

The VVTi, VTEC and other variable valve timing and dual runner intake setups try to get the best of both worlds by switching up the cam timing and intake runners at certain RPMs. You can get both better low end torque and more high rpm HP together.

By the way, interesting to note on this topic, the new GM truck adds that poke fun at the new Ford F150. They say Ford needs to go back to the drawing board and give the new F150 more HP to keep up with the GM truck.

One of the new features of the new motor in the F150 is a three valve head with varialble valve timing. It makes more low end TORQUE at lower RPM than any previous motor of similar displacement. THAT is what you want in a truck for towing, not max peak HP.

SoonerFan

iTrader: (5)

its like my sig says. people get caught up with hp. torque is what gets you off the line. more torque equals quicker 1/4 mile times

NewLoveI30

Or we could just say, torque IS horsepower... Well sort of

SoonerFan

iTrader: (5)

torque
http://science.howstuffworks.com/fpte4.htm

power (HP)
http://auto.howstuffworks.com/horsepower1.htm

how they work together to create speed (shows a dyno with two diffirent engines with similar horsepower. but one has alot more torque to reach the same speed since it is heavier)
http://science.howstuffworks.com/fpte5.htm

Dohcser

Not at all! As other have stated above the scientific term, it is easiest described as (torque) is the actuall power and HP is how fast can it deliver that power.

spirilis

iTrader: (2)

I think this topic has confused me many a time, however I do believe I got the hang of it.

If you consider the operation of an engine, i.e. the 4-stroke cycle of the pistons, torque is related to how much air/fuel mixture burns in each cylinder during one power stroke. So no matter how much HP your engine makes, if you got a tiny engine hauling a heavy vehicle, it's gonna be a dog because each individual power stroke produces very little power.

However, when you go and consider how much energy is actually flowing through the system, the amount of air/fuel burning in each cylinder isn't enough. You also need to know how often it's doing this, which will give you a perception of how fast the fuel is flowing, how much air is coming in, etc. To compile that idea, you must take into account engine RPM. Engine RPM tells you how "often" these power strokes are occurring.

So with those two factors in mind, you can start to imagine how torque and HP play in a 4-stroke gasoline engine.

Torque definitely gets you off the line. The more air/fuel you can shove into a cylinder, whether by making the cylinder bigger, or forcing it in under pressure (boost), or making the airflow more efficient so that the maximum amount of air/fuel can flow in during the intake stroke's duration, the more torque your engine produces because your engine burns more air/fuel per power stroke.

However, now we add transmission gearing to the equation. Low gears amplify torque by trading speed. The longer you can stay in a low gear, the better overall acceleration your car achieves on the track. However, staying in a low gear for longer means the car must be able to produce adequate torque at really high RPMs, which requires the capability of producing a lot of HORSEPOWER, because producing decent torque at high RPMs requires a LOT of air/fuel/exhaust flow.

So now we address the other question--how can a car produce very little torque, but produce lots of HP? Easy. It produces little torque, but it is capable of producing it at insanely high RPMs. A car (#1) that produces little torque, but lots of HP in comparison to a car of equal mass (#2) that produces lots of torque, but equal HP will play out such that car #2 pulls off the line quicker, but as it winds out it eventually has to upshift, while car #1 is still in its lower gear (since it can maintain torque up to a higher RPM than car #2). So while #2 has a head start, it loses it when it upshifts into a higher gear while #1 is still in a lower gear. The loss is due to the fact that car #2 is in a higher gear, which means less wheel torque. Usually much less.