policyvote

Sorry to do this RG, but I'm pretty sure I once used this phrase in a post and you quoted it and said "you mean 'low-RPM horsepower'."

If I've remembered correctly that it was you, then consider us square. If not, then, uh, I hope you can take a joke.

Peace
policy

rotarygod

Both would be correct due to their mathematical relationship although horsepower would be more relevant and the important factor in making the car faster so you are correct. I should have used the term horsepower. Torque is a worthless figure to know when it comes to engine performance. Horsepower is what does work. Torque does nothing.

carbonRX8

iTrader: (1)

If you are going to get all technical then; Horsepower is what does work in some amount of time. Hopefully the shortest amout of time.

You mean it tells us nothing? Realy? Why? If we know that most production cars have redlines around 7k and I have one car that has lots of torque and another that has very little, certainly this is useful info?

Or are meaning that torque does no work.

Tirminyl

You are the first person to ever say something like that. Normally, I hear the exact opposite.

Brice-RX8

Torque gets you there, Horsepower keeps you there.

globi

So for instance, if you sit on a tree branch (and therefore apply torque) you eventually get somewhere?

tuj

This argument comes up way too much on car boards. http://vettenet.org/torquehp.html

Basically, the way I like to think of it is that torque is how wrong of a gear you can be in and still get acceleration. Another way to think of it is that the torque curve is the first derrivative of the horsepower curve. A third way to think of it is how much power you get out of the engine per revolution. Horsepower is like multiplying that amount of power by the number of revolutions the engine is spinning at. Those are all way to conceptualize it, although none are exactly technically correct.

Still think torque is king? Tell that to the F1 drivers who only have 100 lb/ft of torque, but over 900 hp.

globi

You don't have to go on a vette-forum, just do a search on torque (titles) and you find more than plenty on this forum.

therm8

I get so sick of the torque vs horsepower discussion. Without the torque, you have no power. One is not more important than the other. They're both simply measurements. Apply x torque for some amount of time and you get power. Sure an F1 car might make 100lb-ft of torque and 900hp at a given rpm, but if you build an engine that makes 200lb-ft of torque at the same rpm...

and besides the physical value that matters most is friction. after all without that you're just spinning your wheels.

globi

Actually horsepower is not measured. Torque and rpm is measured to calculate horsepower.

rotarygod

Take a bar, pole, etc and clamp it in a vice with 1 foot of it sticking out. Now hang a 10 lb weight on the end of it. (or a 100 ft long pole with a 1 lb weight on it) Ignoring the weight of the pole itself and pretending it is 0, it is exerting 10 ft lbs of torque on the vice. Tell me how this is doing any work. It's just sitting there. Torque does no work. Now if the vice moved it, it would then be doing work but that would also be called horsepower. In order to be doing work you have to have a given amount of time in the equation as well. It's the time aspect that makes it possible to have horsepower and do work. If we have no time, we can still have torque. We just can't have horsepower. Torque itself does nothing. It is just a resistance to twist.

When people say their cars are faster down low because they have more low end torque, this isn't technically accurate. Remember torque does no work, horsepower does. Therefore they must have more low end horsepower also and they do. It's all about the mathematical relationship that allows you to interchange terms and get the point across but technically torque does no work. Alot of people like to think in terms of torque and I admittedly will use the term from time to time just because alot of people think that way and it makes the point. What makes anyone think that low end power is determined by torque but top end is determined by horsepower? Why should it matter what rpm you are at? You are still doing the same thing. Torque is an important number to know because without knowing it and a time reference, we can't determine what is truly relevant and that is horsepower. The V8 guys love to talk torque and they can all they want. I'm not going to argue with them. With those big engines and all those parts, of course it's hard to turn them and hence more torque.

rotarygod

If one car has more torque, it has more horsepower. That's what does the work and that's why one would be faster.

carbonRX8

iTrader: (1)

^^ Thanks.

Sorry if I was not clear. I was NOT trying to start another torque/hp discussion. (please dont, they are boring.) I was asking RG to clarify his point as far as the INFO that hp and torque give pertaining to the performance of a given car. I know what the terms mean. I was just suprized at the comment.

BTW There are dynos that measure hp directly. In that respect you could say that Torque is not measured directly. Just the angular acceleration of a known mass with a known angular moment of intertia. At that, really, dynos just measure descrete rpm (of a known mass) at specfic times. (plus your car's rpm)

Mazmart

iTrader: (12)

Sorry, just had to correct this. F1 engines are closer to 300 lb/ft max torque and just for interest sake the R26B 4 rotor engine has been known to make as much as 470 lb/ft at 7500 to 8000; not all that shabby.

globi

How do you measure hp directly? With a hpenometer?

therm8

The combustion in an engine provides a force to move the rotors (or cause angular acceleration of the rotors). This causes torque on said rotors, which being connected to the e-shaft and thus the drivetrain and wheels, causes torque on the wheels.

All this time the engine is doing, essentially, angular work, which is useless to us atm. Now slap some tires on the wheels and add friction into the mix, and the car moves. Now we have some useful work (or Force (friction) * distance). Now if we do this work over a given amount of time, we get power. Power does not cause work, it is a measure of it with respect to time.

So, the torque on the drivetrain caused angular acceleration of the wheels which combined with the friction of the tires perform the work, which when taken relative to time results in power. (Well really chemical energy is the ultimate cause of all this stuff, but that's pretty much too narrow for this discussion)

Thus torque gives us the useful movement of the car and power is simply looking at this over time. Neither is more important because they are simply the same things looked at in different frames of reference. Power is just a calculation to change torque into something useful for real world applications. Torque and power go hand in hand, since we're dealing with a system that moves around the pivot point.

Peak values are just marketing gimmicks, that everyone falls prey to from time to time.

carbonRX8

iTrader: (1)

horsepowerometer? Yes. Measure work over time. This is done commonly two ways, both with a water impeller. either measure the increase of temp of impelled water over time or measure the work done by or on a impeller over time. If I am not incorrect, many engine dynos are of the impellor type.

Deslock

Wheel torque is what matters and for any given vehicle speed, you maximize wheel torque by maximizing power, regardless of engine torque.

Brief elaboration on that here.

Deslock

That article is misleading and contains some mistakes. It's unfortunate that it keeps getting quoted in various forums.
You can apply torque for an infinite amount of time and have zero power.
You can do the math in terms of work, but it usually unecessarily complicates things.

globi

Deslock makes a great point here.


But back to the horsepowerometer.
What I meant is that you can't measure power with a single measurement device. You just confirmed it yourself. You mentioned over time more than once. This means you obviously need to measure time in addition to other parameters to be able to measure power.
When you dyno an engine you normally measure rpm in addition to torque (brake dyno). (RPM is a frequency which is obviously also a 'timed' unit.)

carbonRX8

iTrader: (1)

You make a good point, but these devices do measure instantanious power as long as you know the mass of the water impelled by the impellor at the measured rpm of the impellor (not engine rpm; this measurement is independent of the engine rpm as opposed to the dynojet torque to hp calculation). you can measure average power also. I was just trying to be "explainitory" and be rigorous when I said work over time. Sorry.

As for a dynojet, when I mentioned RPM, I mean you measure the RPM of the big cylinder that your wheels are in contact with at discrete time points. You calculate torque from the tangential slope of rpm vs time at any point. You obviously need to know the moment of inertia and the mass of the cylinder. So really, hp and torque are calculated in this case. Interestingly, torque measured this way is based on the assumption that the cylinder is massive enough that the torque applied to the cylinder from the wheels is not affected by the change in torque as the engine increases in rpm. (this is a little confusing without resorting to equations and math lingo) It is not a assumptionless calculation.

globi

Actually you also need to know the inertia of the drivetrain (including wheels, axles, gearbox, clutch, flywheel, crankshaft etc.) (and which of course nobody does). Different cars have different drivetrains. Another reason why you can't compare HP data from different cars on a 'drum-dyno'.

This is the way you'd want to dyno a car:
http://www.dynapackusa.com/

carbonRX8

iTrader: (1)

To calculate bhp? Yes, you are absolutely right, but you could just do and engine dyno!

EDIT> I just checked out that link. Way cool. I am going to go do some reading. THanks

therm8

Not in the case we are talking about (unless you have really good brakes). What you say is true, if the system doesn't move around the pivot. Which wouldn't make for a very good engine...


All of which I stated in the part you didn't quote.

Deslock

Below is your entire post:Even in this context, you would've been more accurate had you written "Apply x torque at some angular speed and you get power".

Additionally, power *is* more important than engine torque since you can make a lot of wheel torque without a lot of engine torque, but you can't make a lot of wheel torque without a lot of power (except when you're at very low vehicle speeds).

Case in point, two otherwise identical cars travel at 60 MPH. The one making 400 ftlbs at 3000 RPM has less wheel torque than the one making 300 ftlbs at 5000 RPM.

Having written that, I do like your 47k RPM F1 engine.