i think i figured out where this negativegeforce guy is fucking up. i know it sounds like an elementary mistake, but he's confusing velocity for acceleration. as simple as it sounds, it's the same problem people learning basic calc make when they have to take the second derivative of an equation...

a car can move faster at one rpm range than another, and still be accelerating at the same rate. which is why, in hybridss's hypothetical example, the car will accelerate at the same rate between 4000-5000 and 6000-7000rpm since it'll make the same amount of torque in both those ranges, but (depending on the power band), it most likely won't be moving at anywhere near the same speed in one as the other.

i wish i understood this stuff better.

 

why isnt anyone listening to this guy? hes absolutely right

 

Maybe this will help some of you guys...its a better explaination:

Horsepower is related to torque, and torque is turning force. Place a lever on the engine's crankshaft and measure the twisting force produced, and you have torque. Note that time is not a factor - torque can be constant over time. Horsepower, on the other hand, is the rate at which the torque is produced.

Horsepower is a measurement of the engine's ability to do work. One horsepower can lift 33,000 pounds up one foot in one minute. Horsepower is measured over time. The more horsepower a vehicle has, the more mass it can move in the same amount of time, or it can move a fairly constant mass (the weight of the car) in less time. In simple terms, to get a vehicle accelerating quicker, we need to produce torque faster.

Like I have said, horsepower is the actual work the torque is doing. With no horsepower the engine wouldnt accelerate as fast. With no torque the car wouldnt accelerate fast. You need both torque and horespower to accerate because torque and horespower are tied together.

Horsepower is calculated from torque over time. So it is important to have torque, but it is useless if it cant be put to work...

another bit from an article:

To achieve good performance, operate the engine at its peak torque, and the lower the rpm this occurs, the stronger it will pull from a stop. I see too many "hot-rodded" engines where all they go after is maximum horsepower at high rpm. If you have a light vehicle, steep axle gearing, and are willing to constantly rev the engine high, then high horsepower numbers will make you go fast. Great for racing.

For most of use however, it is better to have an engine with higher torque ratings and the lower or broader the rpm range it achieves it the better. Torque is what gets your vehicle moving. For everyday driving, I would pick a vehicle with high torque ratings at low rpm over a high horsepower, high rpm one any time.

Want the best of both? Then consider vehicle with a supercharged or turbocharged engine. By packing more air into the engine, torque is increased dramatically, but the engine can still be built for high rpm operation. Who says you can't have your cake and eat it too. Unfortunately, cake costs money, and so do superchargers and turbo's. There is always a catch.

 

NGF..not trying to WIN any arguement here...but your still struggling with the idea of HP and its relation to TQ. The #s for TQ and HP will correspond exactly on every single dyno graph youll ever see.

For instance every single car on the planet that makes 200 ft/lbs at 6000 rpm WILL be making 228.48 HP at that rpm. You get the HP figure from the simple equation of 200 ft/lbs x 6000 rpm / 5252 = 228.48 HP. Its as simple as that all HP figures are derived from TQ at whatever RPM its measure at.

So do this as a mental exercise. Get out an old dyno graph or print one from online of an engine you are familair with. Make it a naturally aspirated engine. Look at it....then pretend we are going to add a shot of nitrous at 5000 rpm. Yes that nitrous shot will increase the HP...but what we really have done...is increased the cylinder pressure on every compression stroke which pushes down on each crank journal which in turn increase the TQ output of the motor. So what we have done by spraying nitrous on that motor is increased the TQ. SO on our pretend motor. Calculate how much TQ you would like to shoot for at a given rpm to be increased by the shot of nitrous...and draw a new line. Then...using your new line...find the new TQ number and plug it into the eqaution of Tq x rpm/5252= HP. Do this for several spots over your usable rpm range and connect the dots for a rough estimate of you new Tq and HP lines on your graph. This will also tell you how much you will have to spray to achieve you HP goals.

I personally shoot for a flat TQ line when designing a nitrous motor.

 

Did You Tell Karen?

 

Dude I know exacly what your saying. HP is just a calculation of torque being used. Maximum acceleration is when the engine produces the most horespower and torque in its powerband.

Even though torque can be thought of as the defining point where power is made...its really not! The faster your engine uses that torque the faster it will accerate.

Thats why supras can outrun higher torque and lower reving v8's in a roll. All the torque gets used better and faster in the higher speeds or higher revs.

I think a mix of both good revs for hp and displacment for torque is the best combo for a street car.


I think we just have a different point of view to where hp is coming from.

 

Heres one way of explaining it...say we have a high reving engine here...2 liters.

engine makes peak torque at 4000 rpm at 100 ft lb of torque and stays level to redline wich is 10,000 rpm.

Now...Would the car accerate the same from 4k to 10k? NO. The torque is being used faster and faster in the same time of space...THUS accerating the car much faster at 10k rpm then 4k rpm. Torque just defines the power, but horespower is there for a reason too...to show how fast that torque is being used...

Why the FUCK would anyone create such a scale? Because torque isnt everything when it comes to acceration and power.

I think horepower is a good way to advertise the car's power because it both defines the torque and well it actually could be usefull when talking about the overall power of the car. Horsepower isnt there to just sell the car, but to show exacly what the car is doing with the torque.

If torque sold cars I guess everyone that makes cars would just give the car a nice peak in the lower rpm and throw horsepower out the window. Horsepower can be more then torque in most smaller/higher reving compact cars, but why not advertise torque in the lower hp/higher torque cars? There are reasons that most people may be too ignorant to really know why things are they way they are. Horsepower is a easier way to simply state the engines acceration power since it does include the torque and how much is used...2 bits of information in one number. EASY

 

YES...yes it would accelerate at the same rate. Minus the drag from increased wind resistance of course.

 

its the only thing
Good point...Thats why i believe everyone throws around the HP figure the way they do. It is easier to make certain inferences from just hearing the PEAK hp #s that everyone is so quick to throw around.


your still confusing the term TQ and associating it with LOW END POWER. TQ can be anywhere in the power band. From idle to redline.


HP can NEVER be more than Tq x rpm / 5252 never ever ever

 

You are wrong in your theoretical case.

If the car was operating in a vacuume then the car would have the same acceleration from 4K to 10K RPM.

Since the car has to deal with increasing drag at increasing speeds in your specified case the car will accelerate slower as speeds increase even if torque remains the same.

The best clarification for this debate is that torque is what accelerates cars but it takes HP to battle drag and reach high speeds.

For example my 930 was the fastest production car of the 80s. Bone stock it only had 295 HP at 5500 RPMs but what made it accelerate quickly was 420 ft-lbs of torque at 4000 RPMs.