ok, i think this is the right forum.

engines make torque. hp is a measusrement of torque, as given by the equation:

(torque X rpm)/5252 = hp

torque moves the car, and turbos make torque. the torque curve slopes downward at a certain point, at which the engine's volumetric efficiency is starting to decrease. however, the hp curve continues to slope upward, as there may be less torque/revolution of the crank, but there are more revolutions/minute. so...why do people concentrate on hp and not torque? i just don't get it. given my understanding of this (i may be wrong), i would want more torque. for instance, i think the s2000 engine (and most honda and toyota vtec/vvti engines) are kinda pathetic. i mean, the s2000 makes 240hp, but only 153 pounds of torque. yes, the s2000 is fast, but it's only that way because it redlines at 9 grand or whatever. as a counterpoint, some porsches have flat torque curves between certain rpms, like 300 ft. lbs from 2500-4500 rpms. i would rather have that, than something that peaks at 4800, then drops off, but i keep revving to 6750. i just don't see what's so great about hp.

 

quote from import tuner: HP wins races, torque is for burnouts.

both are correct. torque shows the raw power the engine has.

But Hp shows the total work it can do and the potential is has.

Thats why when looking for an engine they show HP and torque values.

you need both to compare an engine.

[ January 02, 2003, 01:34 PM: Message edited by: Shadohh ]

 

i agree with you in that hp is the work the engine can do, since it's how much torque it's making/revolution as a measurement of rpms. however, i completely disagree with you on your quote from hp. hp doesn't move the car, it's torque. i think it would be more accurate to say rpms win races, rather than hp. if i made 100 pounds of torque, but ran my beta to 15,000 rpms, i'd have 285 hp. if i had 220 pounds of torque, and ran it to 6800, i'd have the same amount of hp, 285. it would be a lot easier and safer to have 220 ft. lbs of torque at 6800 in my beta than to run it to 15,000 rpms, and God knows what the volumetric efficiency is on a beta at 15 grand. i doubt it would be anywhere near 100 ft. lbs of torque. and about the burnout part of the quote, when i do a burnout, i try to rev the engine as close to the torque peak as i can and dump the clutch. i'm looking to unleash the maximum amount of torque i can to the tires, not the maximum amount of hp.

[ January 02, 2003, 01:45 PM: Message edited by: turbulence ]

 

turbulence-

The part you are missing from the equation is TIME. You are completely missing that point.

Using your anology, 285 HP at 6800 or 285 HP at 15000. (let's forget about physical impossibilities of spinning to 15,000...let's just accept that for the moment!)

The engine that spins to 15000 will be making MORE power for a LONGER TIME. From say 10000 RPM to 15000 RPM, that engine will be making in excess of 250 WHP. That gives you a 5000 RPM sweet spot to stay in when racing. It also means fewer gear shifts. Sure our mythical 15,000 RPM motor won't have much toruqe at 1000 rpm or even 3000 RPM, but, that would aid in drag racing helping to reduce wheel spin, and also easing lauches. While the 6800 RPM motor might jump out to an early lead at the 60 Ft mark, and might even still have the lead at the 330' mark, given proper gearing, the 15000 rpm motor will easily supass it by the 1320'.

Your 6800 RPM torque monster has a narrow 4000 RPM power band (2800-6800). The 15,000 Screaming monster more than likly has a 5000-7000 RPM sweet spot(8000-15000).

If you were to plot out both engines on a dyno, the area under the torque line to 5252 rom and the area under the HP line AFTER 5252 is "power" (Regardless if you call it HP or torque) The 15000 rpm motor has more "power"...more area under those lines than the 6800 rpm motor. It makes the same "power"...but it makes it LONGER (over more time).

 

i see your point about the area under the curve. however, i don't think it's impossible to have a beta turning 15 grand...with the right amount of money, that is. i mean, just think about f1 cars, and the 17,000+ rpms they run. however, i was also trying to make a distinction in this post between the two. like i said, engines make torque, and hp is a measurement of that and rpms, and that torque is what moves the car. however, i'm not a fan of nhra or drag racing, but i'm pretty sure the top fuel guys don't shoot for really high redlines. i always thought they tried to get big displacement motors with massive blowers to create gobs of torque. i remember reading that the twin-screws they use make like 4000hp, but take 800hp to turn. i guess i thought that they just tried make gobs of torque and use really tall gears to reduce the number of shifts. i mean, with our two hypothetical, contrasting engines, wouldn't it be better to have lots of torque to go through really tall gear ratios? also, given my analogy of porshe engines, having a broader, or even flat, torque curve may yield the same or even more area under the torque curve. i'm not trying to be argumentative, it's just that not too many people know enough to discuss this with me, so i'm left to my own devices to try and deduce some sort of answer. that's why i posted. i really want to understand this.

 

Turbulence, you are right. Engines create torque.

To make sure we are on the same page, I'd like to define the terms. If you disagree, say so.

Torque is a force that rotates. The unit of measure is pound-feet. If you have a wrench 1 foot long and apply 200 pounds of pressure, you have created 200 pound/feet of torque. If you have a wrench 2 feet long and apply 100 pounds of pressure you also have 200 pound/feet of torque. If my engine has a piston mounted 2 inches off center and combustion pushes down on it with 400 pounds of force, then I have 66 pound-feet of torque. (a simplified example)

Horsepower is a measurement of foot-pounds per minute. Defined back around 1800 by James Watt. 1 Horsepower is 33000 foot pounds per minute.
(330 pound moves a distance of 100 feet in 1 minute. Or 3300 pounds moved 10 feet in 1 minute.) For cars, the time unit used is seconds. 1 HP is 550 foot-pounds per second.

The horsepower rating we have for our cars is calculated based on the torque the engine creates (or is capable of creating). So when I say "My tiburon has 140 Hp at 5800 RPM". What I am REALLY saying is "The engine in my tiburon creates enough torque at 5800 RPM to move 2820 pounds (the weight of the car) 27 feet per second."

Its a matter of semantics, I think. and it can be confusing.

Calculating HP from measure torque (on a Dynometer) is one way to go. Another to calculate HP from trap speed in the 1/4 mile. You can go here and see how to do it. The article argues this is a much more reliable way to gauge HP than calculating from a torque value. I tend to agree. Since here what being done is converting the distance speed and weight into a recognizable number in a standard agreed formate (that is, footpounds per second). If I drive my 2820 pound car a 1/4 mile at a speed of 86.34 MPH. I can convert miles to feet and hours to seconds and arrive at footpounds/second.

So the 2 measurements are essentially different. Torque a measure of force. Horsepower is a measure of work over time. To accurately rate of compare engines we need both numbers. This page has an example about 2/3 of the way down comparing torque and hp, that illustrates the difference well.

I'm not explaining this exactly right, but I think I'm making sense. What do you think?

[ January 02, 2003, 08:04 PM: Message edited by: blue2000 ]

 

very well stated. i didn't want to elaborate that much on it, but you got my exact point. when james watt determined what a horse power was, he got it from a horse lifting coal out of a mine over a pulley. a horse can't lift/move 33,000 pounds 1 foot in 1 minute, and a horse can't move 1 pound 33,000 feet in one minute, so the numbers used in his discovery/example have to be realistic. however, i wholly agree with you on the calculation of hp from 1/4 times. using that method, it's nothing but numbers and math, which don't lie. i would want to elaborate on how you defined torque, though. torque isn't a force that rotates. it's a measurement of force applied to one end of an object, while the other end is somehow anchored. it's a "twisting" force. exactly how you said a piston pushes the rod down as a result of combustion. the piston is "torquing" the rod against the crankshaft. i think what my problem is is that this is kind of a theoretical debate, as opposed to some objectual, or numerical debate. i still firmly believe that the hp measurement is somewhat less valuable than the torque measurement, but then i think that it also depends on the application. i agree with random on what he said, but what if i had a flat torque curve, as in my example, with as much area under the torque curve as the 15,000 rpm engine did from 8,000-15,000 rpms? to me, that seems more logical, as it's easier to create more torque on and engine in lower rpms, than to design and engine to be volumetrically efficient at 13,000 rpms, since the pressures exerted on the piston, and engine as a whole, are less. i mean, if it were easier or just as easy to create some amount of torque either using low (relatively) rpms and boost, or high rpms and volumetric efficiency, then why wouldn't companies (maybe even confined to exotic car companies) go the route of high rpm?

 

I don't think its a matter of one choice or the other, or which is easier. It's a matter of choosing a method that fits the application. A truck hauling a 5000lb boat needs power developed in a different way that a Ferrari going 100 MPH on a straightaway.

 

i see your point. i did say somewhere that application matters, but i don't think it was in the way that you said it did.

 

Turb, I think you are making this harder on yourself.

HorsePower

The definition of 1 horsepower is the ability to do 33,000 pounds-feet of work in one minute. So horsepower is a measurement of torque over time. The measurement of horsepower was invented by James Watt when he replaced horses turning a water pump with a steam engine and wanted to know how many horses the engine could replace in order to rate the engines power. He figured that a horse could pull with 180 lbs. of force. The horse traveled in a circle with a 12 ft. radius, and could make 144 complete revolutions in 1 hour. This means that the horse traveled 181 feet per minute. 180 lbs. of force times 181 feet equals 32,580 pounds-feet of work in 1 minute. Watt rounded that up to 33,000 pounds-feet of work in 1 minute.

A BETA WILL NEVER REV OVER 7500.

Get over it.