Torque vs Horsepower: Auto Racing Power Showdown

[rcgldr]

For the 1967 season, the Lotus F1 race car (400 hp, 1400lb with driver and 20 gallons of fuel) had 1st gear set to redline around 100+mph, and 5th gear set for around 190mph to 200mph depending on the track. Gearing is track sensitive (choose gears to avoid extra shifting), but probably rpm drops around 30%, 20%, 15%, 12%, would be typical. Still to avoid an extra shift, a car might exit a turn in a higher gear, so having a power band for the upper 30% to 35% would help. A narrower powerband could be an issue if the jump in torque were sudden, making throttle inputs difficult to deal with in turns.

For a 6 speed tranny, the Suzuki Hayabusa motorcycle gears are set to redline at these speeds (actual top speed is around 190mph): 1st-80 mph, 2nd-108 mph, 3rd-137 mph, 4th-162 mph, 5th-183 mph, 6th-199 mph, for a rpm percentage drop of: 35%, 27%, 18%, 15%, 9%. 80% of peak torque is available from 3500 rpm to 10,500 rpm, about 2/3rds of the rpm range.

 

[u83rn00b]

Torque=force times distance, horsepower=power

 

[ME_262]

Well this is my first post here, I stumbled on to this thread with google looking for an answer to some questions I had.. I've learned quite a bit

Basically I've figured out that torque is better than HP every time... if.. and only if there was no such thing as a little thing called gearing.

Bring gearing into the picture and it's a whole new ball game. Even better bring in the ideal CVT and the inverse of the above is true.

Before reading this thread I was under the misconception that 200Lbft at 3000RPM accelerated just as fast as 200Lbft at 6000RPM. This is true if gearing did not exist. But because it does you can trade the extra distance of the 6000RPM for more force and accelerate faster than the car at 3000RPM.

Basically it comes down to the amount of Watts or horsepower the car outputs, the higher this number the more it can be geared into torque at the rear wheels. And undisputedly in all cases, torque at the rear wheels is what will win you races.
Edit:
(Torque at the front or all wheels for some lol)

 

[punx0r1337i57]

I just had to put my 2¢ in on this one...

Torque is a pretty useless figure, but it can be a reflection of low RPM HP, and by extension, often reflect a wider power band.

HP is a much better figure, but the HP number you are given is peak HP, which in and of itself isn't too useful either in an automotive application unless the powerband is wide or you have a lot of gears.

Ultimately, the best data you could get would be a HP curve from idle to redline and all engine speeds in between.

See, the power a car can produce is inherently based on speed as much as force, which torque doesn't take into account. If I stood on a 1 foot long wrench pointed out at a 3:00 or 9:00 position, I would be putting 160 lb/ft of torque onto it. Which is more than my car. Does that mean I could pedal my car faster than the engine can pull it? Of course not, because in order to move the 3,000lb boat, I'd have to change my pedaling to a very slow speed. Even though I can produce that much torque, I could only get it around a few times a minute, resulting in less than 1 HP. Which is a better representation of how much power I can actually produce.

But before the torque elitists jump on me, peak HP doesn't mean too much either. Suppose a car can produce 200 HP at 6,500 RPM, but it produces only 50 HP at 6,000 RPM and redlines at 6,600. (Of course I'm using extreme examples for both of these, I'm well aware. I'm illustrating a point.) Unless you can shift really fast and have a few dozen gears (or a very effective CVT) you've got a dog-slow car.

Basically, what I'm saying is, what makes you fast is a good, wide curve of high HP. Torque is in and of itself completely useless, and peak HP is only worth marginally more. The value of these figures is in what they can reflect (but don't always, which is why both are imperfect figures.) Torque peaks are at lower RPMs, so they generally reflect how low down your powerband appears. HP peaks are higher and generally reflect how long an engine's powerband lasts at the high end.

So let's take it to a real-world situation. Let's take the most extreme examples of HP vs. Torque and compare them.

Honda Civic Si with the K20 engine, and a Chevrolet Camaro RS with the Throttle Body injected engine (This is late '80s, early '90s model).

The Honda comes in the lead in peak HP with 197 against the Camaro's 170, but the Camaro's mammoth 5.0 V8 has 255 lb/ft of peak torque, versus the Honda's measly 139. So which is better?

These are published 0-60 times:
Camaro: 7.4
Civic Si: 7.2

Of course, people have gotten better times on both with stock cars, and both can be a lot faster with modification, so don't flame me for conservative figures. Those are both official published figures.

So what do we have there? Not a whole lot of difference.

The Camaro will have much more power at the bottom. It's 170 HP comes at an astonishingly low 3800 RPM, courtesy of its huge displacement. The Civic, by comparison, feels its engine's tiny displacement, and by its torque peak of a far higher 6200 RPM is still falling behind at 164 HP (remember, HP is torque x RPM / 5252). Up until this point, advantage: Camaro.

However, shortly after that, the Camaro feels its archaic pushrod engine design and quickly starts to dump torque, and consequently HP to friction, inertia, and poor ventilation as RPMs increase, and then it chokes on its low 5,000 RPM redline. The Si, by comparison, breathes much better through 4 valves and doesn't have pushrod inertia and keeps increasing in power until a dizzying 7800 RPM, and then it keeps running at well over the Camaro's max output past its 8,000 RPM redline up until about 8,250 when the rev limiter cuts you off. Advantage: Si.

So which is ultimately better?

Well, that depends. The Honda is ultimately faster. But it is absolutely useless with an auto, which runs in the low RPM range, hence why all Si's are manuals. And you have to know what you are doing. It is much easier for a novice driver to run a 7.4 in a Camaro than a 7.2 in an Si. In the Si's defense, it also uses a lot less gas and weighs less, allowing the car to corner better.

Ultimately, it comes down to the driver. Proving one to be better wasn't my intention (the comparison is ridiculous anyway... a 15 year old car with a 5L V8 to a new car with a 2L I4) and I don't drive either, so I don't much care. The point is, neither is a perfect figure, and are in fact, in and of themselves, pretty useless. Their value is in reflecting points of an overall HP curve.
However, I do have a bone to pick with Briggs & Stratton for using torque instead of HP on their new engines. Peak horsepower really *is* the best figure on small engines that run at a constant RPM, and I think they are just using torque (which is, to be honest, a pretty useless figure on a generally fixed-speed engine) to jack up their performance figures since they are increasingly unable to compete in HP per CC against Honda and Robin engines with OHC valvetrains and are confusing the whole small engine comparison process along the way.

Alright, that's enough for now.

 

[rcgldr]

Camaro vs Si 0 to 60 times

There's more going on here than just torque and power. 0 to 60 times can be affected by how much momentum is built up by the rotating mass of the engine and flywheel. The Camaro with rear wheel drive, and a lot of engine and flywheel mass, is going to get a lot of help with it's initial launch, regardless of the torque and power it makes. 1/4 miles would be a better indicator of power.

 

[ME_262]

The only way I could see torque peak being a valid number, is if it was a device that ran at a constant speed and ran at a 1 to 1 ratio with the engine. In a 1 to 1 ratio with none of the RPM being geared down for extra torque, the torque peak is the point where the device would output the most power.

In addition to this, this is because the overall output of any engine is indeed torque, it is changed from the torque value in the engine by gearing, but giving the output torque would also be valid to me.

 

[rcgldr]

In a 1 to 1 ratio with none of the RPM being geared down for extra torque, the torque peak is the point where the device would output the most power.

The most power always occurs at the power peak. In a fuel buring engine, the power peak is alway at some faster rate of revolution than the torque peak (assuing that torque versus rpm doesn't fall off vertically as some magic point, or due to a rev-limiting device set at the torque peak).

In 1 to 1 applications, such as aircraft the prop pitch and diameter are choosen to work with the power range of the motor, so in effect, there's still the equivalent of gearing. In the case of a car with a 1 to 1 gear the diameter of the wheel could be adjusted.

Most electrical motors are more interesting, in that they are almost constant power motors across a wide range of rpm. Torque decreases with increases in rpm, and power remains approximately constant, and it's the load and the input voltage that determines the rpm. Current demands will vary to match the load and rpms. Although output power is nearly constant across a wide range of rpms, the associated input power will vary, and there is a specific rpm where the motor runs most efficiently. So once again, gearing or the equivalent is still used to allow the motor to run at an efficient range of rpm.

To eliminate the need for gearing, "outboard" motors are becoming popular with radio control models. (The housing rotates while the shaft remains fixed). These motors have peak effeciencies at much lower rpms than conventional motors, eliminating the need for gearing. Again for rc aircraft the prop size and pitch still have to be matched with the motor.

 

[punx0r1337i57]

There's more going on here than just torque and power. 0 to 60 times can be affected by how much momentum is built up by the rotating mass of the engine and flywheel. The Camaro with rear wheel drive, and a lot of engine and flywheel mass, is going to get a lot of help with it's initial launch, regardless of the torque and power it makes. 1/4 miles would be a better indicator of power.

This is true, but the Civic is also lighter. It certainly isn't a perfect comparison, but it is the best I could think of. The extra traction of large rear drive wheels probably gives the Camaro an unfair advantage. Plus the fact that that figure is actually for the 190 HP Camaro rather than the throttle body 170 HP model, since I couldn't find a figure for it. Maybe an S2000 would have been better for comparison? But an S2000 really blows the Camaro away, and I didn't want to be accused of being anti-American biased.

Of course, more recent Camaros are much faster than the old ones, but that is largely because they have a much better HP figure, so they aren't so relevant to the discussion.

 

[ME_262]

So basically... I'm trying to unite your thoughts with mine on this issue...

What it comes down to is the horsepower output of the engine which is converted to a torque value at the wheels by gearing. So the higher the HP the faster you are going to accelerate. So for example two cars going down the road both with a 1 to 1 ratio of gearing all factors including tires the same and both making 25HP would be accelerating at the same rate at that instant.

 

[rcgldr]

Well yes, identical cars will have identical acceleration rates (assuming identical driver inputs).

One missing issue here is "drivablity". It's one thing to setup a car for racing where the engine is always kept at high rpms. It's another thing to setup a car for everyday driving where the engine is mostly running at lower rpms. For a street car, having a wider power band is more important than max power, and most street cars are setup that way.

 

[danielrm26]

Greetings all,

I've been grappling with this question for over a year now and I just now found this forum. Excellent content.

I have created my own primer on this topic and I'm wondering if I can get some input from you guys. I'm not a physicist, but I am a hobbyist and am somewhat familiar with the main concepts.

Anyway, my hobby is to try and simplify things into relatively concise explanations; and this primer is one example. As with all my primers of this type, the main goal is to understand the concept myself and then have a reference to come back to. I'd very much like to see what you guys think about it. Is it totally botched? Am I on the right track? What am I missing?

http://dmiessler.com/study/horsepower/

Thanks much!

 

[rcgldr]

Hang on a second, I'm blowing off the dust of this old thread.

Look at this post I made:

post #54

Horse power never "equals" torque at any rpm, they aren't the same units. For specific units, their magnitudes are the same at 5252.113122... rpms, in English units and are the same at 9549.2966... rpms in metric units. If you measure angular rate in radians per second, the magnitudes are the same at 33,000 radians per second for English units, and are the same at 60,000 radians per second for metric units. So are power and torque the same at 60,000 radians per second? A person has 32 teeth, so is it more efficient for that person to generate 32 lbs or 32 Newtons of force because both numbers are 32?

Most chassis dynamometers measure power, not torque. Either a variable load is used, or the rate of angular acceleration of a heavy drum is used. In either case, there are two inputs, the measured force, and the speed at which the force is measured over a range of speeds. In semi English units, horsepower = force (lbs) times speed (mph) divided by 375 (conversion factor). In metric units, watts = force (Newtons) time speed (meters / second). Without additional input, such as engine rpm, chassis dynamometers can't determine the angular speed of the engine, so they can't calculate the effective torque without the additional input.

I did some dyno runs on my old Caterham, and because of issues sensing the spark line, they could only plot the power and not the torque, because they couldn't determine engine rpms. Since a chassis dyno simulates the real world, this should help make it clear that it's power and not torque that determines the performance of a car.

As another example, imagine a small linear inductive motored train powered by plutonium buttons and thermal couples. No internal moving parts (except at the atomic level), nothing is rotating, so there is no torque, but there is power, and the rate of acceleration of the train will be determined by the power to mass ratio (and aerodynamic drag).

A follow up to my previous post:


Some typical flywheel weights for street cars, stock and lightened.

Mitsubishi Starion 2.6 Turbo...35 lbs. stock / 21 lbs. lightenend
Datsun Z car 225mm...25 lbs. stock / 16 lbs. lightenend
Datsun Z car 240mm...28 lbs. stock / 18 lbs. lightenend
BMW 2002 215mm...18 lbs. stock / 11 lbs. lightenend
BMW 2002 228mm...24 lbs. stock / 16 lbs. lightenend
Datsun 240SX KA24DE 24-25 lbs. stock / 16-17 lbs lightened


Flywheel weight of a Formula 1 race car - 4 lbs

 

[46weaver]

Hi All, I am trying to translate the theory into real world situation.
Hope you guys can help me out. Here's my long list of questions -
** note - the hp and torque figures quoted are made up numbers**

1. An engine produces peak 200 lb ft at 300rpm, and peak 220 hp at 5500rpm.
In the same gear, is the acceleration force stronger at 3000 rpm compared to at 5500rpm?

2. A Ferrari engine with peak 300 lb ft at 5000 rpm and peak 400hp at 7000rpm vs a BMW 7 series engine with peak 400lb ft at 3000 rpm and peak 340hp at 5200 rpm
Both engines used on a 1500kg car and same gear ratios (using Ferrari's closely spaced ratio).
Which one accelerates faster?

3. A Ferrari engine with peak 300 lb ft at 5000 rpm and peak 400hp at 7000rpm vs a BMW 7 series engine with peak 400lb ft at 3000 rpm and peak 340hp at 5200 rpm.
Both engines used on a 1900kg car and same gear ratios. (using a BMW wider spaced ratios)
Which one accelerates faster?

4. A Ferrari engine with peak 300 lb ft at 5000 rpm and peak 400hp at 7000rpm vs a BMW 7 series engine with peak 400lb ft at 3000 rpm and peak 340hp at 5200 rpm
Both engines used on a 1500kg car and same gear ratios. (using a CVT transmission)
Which one accelerates faster?

5. A Ferrari engine with peak 300 lb ft at 5000 rpm and peak 400hp at 7000rpm vs a BMW 7 series engine with peak 400lb ft at 3000 rpm and peak 340hp at 5200rpm
Both engines used on a 1900kg car and same gear ratios. (using a CVT transmission)
Which one accelerates faster?

 

[Lsos]

Even if I calculated and answered all 5 questions...or 10, or 50...would you be any closer to understanding what hp and torque is?

If you don't understand something, ask it. When you finally understand it, it's very simple to figure out all the answers yourself.

 

[rcgldr]

1. - Maximum force at the tires in a specific gear occurs at the speed of peak torque. Acceleration would depend on the total opposing force, rolling resistance and aerodynamic drag.

2. 3. - If the distance to accelerate is long enough for cars to get near top speed, then the higher powered car will accelerate faster, although torque versus gearing may help the higher torque lower powered car in 1st gear, ingoring the fact that a clutch can be used in first gear to get around this.

4. 5. - With a CVT transmission, the higher the power, the more torque that is delivered to the driven tires, at any speed.

 

[Fahlin Racing]

Very interesting thread on HP & TQ.

If 'torque gets you moving, horsepower keeps you moving'. This definition fits the best from what I have observed. Then the comments on one or the other being useless perhaps should be discarded. Simply because HP is calculated from torque production. In a piston type engine the torsional rotational we need is just a kinetic version. Maybe if we were to speak about jet engines where we do not use a drivetrain, then torque can very well be removed from 'stat advertisements' then.

If torque were not important, then we wouldn't increase the cubic inch displacement values of piston engines by extending the crankpin throw for more leverage and cubes. Smokey's theory on connecting rod length as fit the longest con-rod in the engine that is suitable, reason was to utilize the piston dwell time ATDC for in-cylinder pressure to build up and effectively push the piston/con-rod. Now if smaller chambers create more rapid pressure rises, I think the long rod theory would still have a slight advantage even today, but with the quality cylinder heads of today short and long rod engines win races. If somebody may use a factory head of 90s and earlier american V8s not-worked, the longer rod could produce a stronger suction on the induction port because of the somewhat slower movement of the piston ATDC. You could say it allows the induction charge to flow with the piston decending down the bore to a point since the long rod is faster at BDC.

Where I grew I heard a little story from someone, that a factory 80s IROC Camaro took a 1971 Nova with a blower in a race. Now I am not sure the story is absolutely true, but I wouldn't doubt the possibility. It all comes down to the 'Tuner's skills'. That includes chassis, engine, drivetrain, tire selection and surface.

From how I believe things get done is 'torque gets you moving, horsepower keeps you moving'. Now building HP & TQ is a whole world in itself.

 

[xxChrisxx]

Oh no! Not this thread again.

Sweeping statements about torque vs horsepower are all wrong, just to varying degrees. (Which is the only sweeping statement that is true). The fact they are so intrinsically linked it depends on the question and what you want to know. Catchy phrases don't cut the mustard.

GEARBOX >> POWER vs TORQUE
The gearing tends to render the very basic questions about torque vs horsepower pointless.
EDIT: Grrr, thread is millions of years old.

 

[jack action]

I never understood why this question was so difficult to answer for most. Let's clear this up.

Looking at the vehicle:

$$Acceleration_{car}=\frac{Force_{car}}{Mass_{car}}$$

$$Acceleration_{car}=\frac{Power_{car}/Velocity_{car}}{Mass_{car}}$$

There you have it: for a given car velocity, acceleration is proportional to power. It doesn't matter if the power comes from an internal combustion engine (ICE), an electric motor or a set of pedal for that matter: No body cares about the torque, power is all you need to know.

And before someone says:

$$Acceleration_{car}=\frac{Torque_{wheels}/Radius_{wheels}}{Mass_{car}}$$

This is not a valid relationship because the torque and radius are properties of the wheels and not of the car. It is impossible to measure the "torque of the car" or the "radius of the car". Furthermore, reducing the wheel radius by a factor of 2 will increase the acceleration of the car by a factor of 2, but what the equation doesn't say is that it also reduces the speed of the car by 2. So, two car-related variables changes with wheel radius: whenever you are gaining in acceleration, you loose in speed and vice versa.

But wait, there is more.

What if power is varying? For example, if we are using an ICE with a know RPM range (say 3000-6000 rpm) where, obviously, the power increases with the RPM.

Then what we care about is the AVERAGE power throughout the RPM range. No matter what is the extent of the RPM range.

Race cars (of any type) will try to maintain a very small RPM range across the peak power of the engine. Therefore, the average power will be very close to the peak power.

But if you take a more useful vehicle and you want to accelerate from standstill, dropping the clutch at 5000 rpm is not recommended such that you can get the peak power. So in such a case the POWER at low RPM becomes very important. Of course, the higher the power, the higher the torque; but what counts is the power.

For instance, a torque of 200 lb.ft@2500 rpm (=95.2 hp) will create a greater force at the tire's contact patch than a torque of 205 lb.ft@2400rpm (=93.7 hp), AS LONG AS THE VEHICLE SPEED IS THE SAME FOR BOTH EXAMPLES. (And for that, the gear ratio or wheel radius will have to be different for the two examples)

So to sum up:

To get the maximum traction force at the wheel (hence the maximum acceleration) at a given speed:

The whole torque curve: USELESS

Peak power: USELESS (unless you can run a very small RPM range and you rarely need to start from a standstill)

AVERAGE power throughout the USEFUL RPM range: DING! DING! DING! We have a winner!

 

[Fahlin Racing]

Yeah, I know its old an thread, so is the topic itself. I just enjoy in-depth conversation on what I love working with, vehicles I've learned some as well.

It's not difficult to comprehend Jack. It is more or less how someone sees the definition of either. I do agree the average throughout the rpm range is what is desired, but, you will need cylinder pressures to generate torsional rotation to begin & proceed with getting work done the quickest, equating to HP being the most concerned when accelerating and keeping vehicle momentum going.

If the torque curve rises from a manifold change & horsepower (or vice versa) does not on the engine dyno or chassis dyno, what is your view on how the car or truck might be different during operation?

 

[xxChrisxx]

When you say the torque curve rises, but the power curve does not. Can you please clarify what you mean?
Do you mean peak power doesn't change or the acutaly power curve doesn't change?

I've seen these threads for ages on many different forums and it always sparks furious debate where non exists. I find them funny but also dread them. It's like some sort of unstoppable monster of baffling comments and sweeping statements. Given long enough, as sure as the sun will rise, you always get the following two quotes:

“Horsepower sells cars; torque wins races” from the torque crowd.
"Without rotation torque means nothing" from the power crowd.

 

[Fahlin Racing]

Yes, I do agree that some people get heated over the topic. HP does sell cars from a marketing standpoint though. Similar to selling heads and bigger CFM numbers. But without a twisting force, torque, we can not generate power in a piston engine. We can have all the math in the world, but it still boils down to the crankshaft rotation in relation to combustion quality in a piston engine to get work done.

What I meant was if a manifold change would increase the torque throughout the rpm range and HP stayed the same throughout the rpm range, how would the vehicle operate in action? If low-end torque prevails coming out of the corners on an oval track, then torque itself is has a place, maybe at lower rpms but it isn't exactly useless from my perspective.

I am curious on your views as well Chris.

 

[xxChrisxx]

The way I read what you are saying is that the torque curve alters (same shape but a shift up in torque output throughout the range), but the power curve stays the same. Which is a situation that you just can't get, if you increase torque across the range power output must increase.

My view is it's pointless making the distinction between torque and power as they are both intrinsically linked, that it makes it a bit silly to make the distincition as to which is 'important'. You can't say one is more important as they are both equal in relevence and indeed directly affect one another, except in very very specific scenarios.

 

[Fahlin Racing]

True, nothing is in fact, fixed. But does not mean its an absolute impossiblity. Would you happen to have any good article links off the top of your head I could read on this simple but entertaining subject?

 

[xxChrisxx]

It acutally does mean it's imposible. The power - torque relationship defines this.

http://en.wikipedia.org/wiki/Torque
P = T*w*2pi/60000 in SI units.

So say you had 100Nm @ 3000rpm

P=100*3000*2*pi/60000 = 31.41 kW

Now let's say we shift the whole torque curve up 20% (as you said) by adding some boost. So now we have 120Nm @3000rpm

P=120*3000*2*pi/60000 = 37.7 kW.

As you can see 120/100 = 1.2
37.7/31.41 = 1.2.

If you increase the torque at an RPM value the power output is altered by the same ratio.EDIT: You can read stuff like this on wiki. I don't have any articles to hand, but I am sure there was something in one of my old Racecar engineering magazines.

 

[jack action]

If the torque curve rises from a manifold change & horsepower (or vice versa) does not on the engine dyno or chassis dyno, what is your view on how the car or truck might be different during operation?

Just like Chris said, at a particular RPM, you cannot increase the torque without increasing the power.

And if you mean:"What are your thoughts about raising the peak torque and decreasing the peak horsepower?" I would answer that this can be good or bad depending on what you do with the engine. By doing so, you have increased the low-end power^[1] and lose some high-end power. If you usually use the engine in the low-end range (say a street car in city traffic) you may find your car more responsive. If you usually use the engine in the high-end range (like a race car), you working against your best interest in any case.

but, you will need cylinder pressures to generate torsional rotation to begin & proceed with getting work done the quickest, equating to HP being the most concerned when accelerating and keeping vehicle momentum going.

Nope, as shocking as it may sound, you don't need torque to get power. Power is proportional to magnitude of the cylinder pressure (or torque) and the frequency at which it comes back (the RPM). A small force that comes back often is just as powerful as a big force that comes back once in a while.

For example, 400 lb.ft @ 2000 rpm produces the same power than 200 lb.ft @ 4000 rpm (152 hp in both cases). You will see absolutely no difference on the car's performance, assuming the car is at the same speed at those RPMs. If we look at the low-end power and, say, with the first engine, @1000 rpm (half-speed) you get 360 lb.ft (69 hp) and for the second one, you get 100 lb.ft @ 2000 rpm (38 hp), you will find the first one more powerful because your AVERAGE power throughout the RPM range is higher. But if you use the low-end rarely, you won't notice the difference between the 2 engines. It is all a matter of what you do with the engine. That is why peak power is a rather meaningless number, unless you are there all the time.

[1] Note that I do not use the usual expression 'low-end torque' even if it is true as well. But raising 'high-end power' also increases 'high-end torque'. Again, performance wise, torque is irrelevant, only power is of interest.

 

[Lsos]

Despite the saying (or perhaps because of it), it seems to me that torque is what sells cars, especially in America. They chilled out with it lately, but for a long time it was the trend to shoehorn as big an engine as possible into every car, with no regard for the horsepower output. I still tell stories here in my country about how my first (and only) American car had an engine 2 times bigger than some Euro econo car they are driving...and it still managed to have less power. It did have a kick from it's massive torque. Just one, quick kick...and then it fell flat on its face.

Anyway, torque is a good thing, but they point of a car engine is power. As long as you have power, you can engineer your way out of even the crappiest torque curve. Might not be pretty, and might not be comfortable, but it's possible to make it go.

However, even if you have a million torques (of whatever unit you want), if you don't have the power to back it up that thing is not going get anywhere in a reasonable time, even if God himself designed the rest of the drive train.

 

[RonL]

Here is how I came to realize to some extent how things relate to each other,...
In my younger days, Don Garlits broke 200mph with a 392 CI hemi that made about 1250HP @ 8,000 or more RPM.
Around that same time we built a push boat that had two 1250 HP Caterpillar engines that turned about 400 RPM, these required a quite large crane to set them in the boat.

When the understanding really started to become clear was when I realized why the two engines could not work in the different enviornments, (speed, weight and time duration).

I think in those early days dragster engines lasted two or three runs before rebuilding or replacing, nowdays I think each run uses an engine to it's max.
Our boat engines, if on an oil tow job, would run nonstop for up to a year or more stopping them only for oil changes or if they started showing low oil pressure it would require a lower bearing changeout. Almost always one engine running while the other was being serviced. Fog and sometime wind would put the boat against the bank.

If you look through power transfer catalogs and study speed and horsepower ratings, you will start to see a pattern of shaft sizes and unit weight, these can be good indicators of the difference between HP and Torque.

This works pretty well for me without too much number crunching, maybe it will help someone else.

 

[annafenfen]

That will be ok :)

 

[Ranger Mike]

RonL
good to know there is another gear head here...
nice to meet you
rm

 

[RonL]

RonL
good to know there is another gear head here...
nice to meet you
rm

Thanks Mike,
I was able to attend the Spring Nationals in Baytown Tx two years ago and found out just how far out of touch I was My first event in over 20 years, I was not prepared mentally for the sounds or the speeds, last time I had looked they were struggling for 250 MPH now they were around 330.

To add insult to injury, I made the mistake of asking a few very savy younger fans around me if they knew anything about Leonard Hughes (response was never heard of him)
Then lo and behold there pops up Joe Tueton running in class (don't remember what) I did not have time to see him in the pits afterwards, I did not know him well, but he might have been able to give me a few updates about people from the Houma area.

It was a great day for an old geezer with locked gears

 

[Fahlin Racing]

Thanks Chris & jack. I appreciate the help with the physics here. I am new to the world. I will continue to read this thread when I can to learn more.

 

[PaulS1950]

The value of torque versus the value of horsepower in vehicle performance has been and will be debated forever.
When we list torque and hp we usually list maximums and the rpm at which they occur. These values help to cloud the issue because someone has an engine with higher peak torque and hp than another but in identical cars the one with the lower peaks wins races. A higher average torque and hp can easily win against an engine with higher peak values.
Torque is necessary to produce hp - that has been said if not so plainly.
Peak torque is produced at an engine speed where the cylinder is most efficient at moving air in and out and cylinder pressures are the highest.
Horsepower is a direct result of the amount of torque produced and provides movement for the vehicle.
Which is more important depends a great deal on the vehicle and its purpose.
A drag racer that uses a light car with a huge engine burning nitro-methane has one purpose - acceleration. It needs rpm to get to a top speed that is competitive and has to survive 1/4 mile at a time.
A slolom car that has to accelerate out of tight corners and achieve speeds of over 150 mph on the rare straights needs a flatter torque curve and rpm to get to those speeds while surviving for 500 miles.
A daily driver - "grocery getter" - needs to operate well at rpm less than half that of the slolom car and perhaps a third the rpm of the drag racer and continue to run for 100000 miles or more.
The car is an operational system that has to be engineered and built for a given purpose. Asking which is more important referring to a single component in that system makes no sense without including its use and the rest of the components that are wrapped around the engine.

 

[Ranger Mike]

RonL
was that Len Hughes of Candy and Hughes rail fame?

 

[RonL]

RonL
was that Len Hughes of Candy and Hughes rail fame?

Yes that's correct. (Candies and Hughes)


http://www.ottocandies.com/current_projects.html


Here's a link to his sponsor in those early days, he had a little single bay repair shop on the side of Terrebonne Bayou which ran through Houma, he would push that first funny car outside while he worked on cars for some of his customers.
Before the funny car he ran the sweetest little chevy, I think it was B stock.

 

[zanick]

I think I might be able to end the debate. It keeps going back and forth. Folks are using and changing terms, perspectives, vantage points, and it all gets pretty confusing.

I mentioned in another related thread, when I was asking this physics group, of what really came first, the HP or the torque. It got a little off track and then I think we all came to an agreement.

I started that thread out by specifically stating that power dictated torque at the rear wheels. Sure, you could figure it out in reverse as well, but generally, there is this argument of what is more important, engine torque or engine HP? Also, the misconception that torque gets you out of the turns and HP down the straight, (as well as hp sells cars, torque wins races) .

Basic physics 101 guys. acceleration = power/(mass x velocity)

This says acceleration is directly proportional to power and inversely proportional to speed.

He who has the most power at any given vehicle speed, will have the greatest acceleration at that speed (regardless if its out of the turn, corner, or down the straight), and therefor, the greatest torque at the driven wheels. No one can debate this. So, most all the talk then becomes relating to the shape of the HP curve over the operational range. (i.e. between all the gears). he who uses the most HP-seconds, will win the race in a straight line. (ignoring the drag racing factors and all other variables kept the same). this is the reason for close ratio gear boxes, and big beefy v8 and v10s with flat HP curves.

What I thought was a more philosophical debate, ended up being not really answered in the previous thread. The though was that it all started with power. doesn't the potential energy of the gas start the process? it rapidly expands as it combusts and pushes down on the piston, that heat energy is converted to mechanical energy (ie force). To the discussion, that can be applied to little tiny pistons that spin a small crank REAL fast. (like a porsche GT3RS engine with 500rwhp, spinning 9000 rpm) or a Viper with an engine making the same 500hp but with the engine spinning only around 6000rpm). Flat torque curve for the porsche, but peaky HP curve, vs the flat HP curve of the viper. who wins? depending on the shapes of the curves and the closeness of gears used, sometimes the viper, sometimes the porsche. But, both at ANY vehicle speed, if they are making 500rwhp, will produce the same rear wheel torque, (not engine torque, measured at the rear wheels) as would be measured at the wheels, after the gear reductions.

So, the bottomline is you want a powerplant that maximizes your HP-seconds. it can be done with big engine torque or small engine torque. if you are comparing two like engines, then you want the one that has more lower end torque, becuase it will have a flatter HP curve and produce more HP-seconds over the useable range.

My main question to the field here, is what other terms or equations can you use to approximate the time element in a HP curve. from a laymans perspective, you will be accelerating over a longer period of time as you run toward the top of the rpm range of an engine, that's why i though HP-seconds was a applicable term. what do the physics guys think or suggest to incorporate this time element into comparisons. area under the HP curve doesn't work completely for that reason.

Thoughts?