Automotive Torque vs Horsepower: Auto Racing Power Showdown

[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?

 

[zanick]

Yep, and God would use a IVT(Infinitely variable transmission) then, it wouldn't matter what the torque of the engine was, only the HP. :)

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.

 

[jack action]

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?

This is exactly my answer in https://www.physicsforums.com/showpost.php?p=2823175&postcount=88".

As for comparing 2 engines, you must begin by defining what is your useable RPM range. Here is an example with 2 power curves from fictitious engines:

When comparing the 2 power curves based on the ratio RPM / RPM max, one would be tempted to say that the red curve is better than the blue curve. But that is only true if you go in the RPM range below 60%. If you can keep the RPM range above that (for example a race car on a track with no sharp turn), then both engines will produce exactly the same performance (though, with different gear ratios).

The important number is the AVERAGE power throughout the useable RPM range. And that last one depends greatly on what the engine is used for.

 

[xxChrisxx]

Thoughts?

My thoughts are you've just repeated the roundabout of 'arguments' that's been happening for 7 pages. The entire debate is pointless, torque and horsepower are both intrinsically linked making this vs debate a waste of time.

As you say for any given vehichle speed max acceleration occurs at peak power. But in a specific gear max acceleration occurs at maximum torque.

 

[rcgldr]

As you say for any given vehichle speed max acceleration occurs at peak power. But in a specific gear max acceleration occurs at maximum torque.

This could be avoided by using a CVT (constantly variable transmission) which could keep engine rpms at peak power regardless of vehicle speed.

 

[jack action]

But in a specific gear max acceleration occurs at maximum torque.

Chris, I know that you understand correctly the physics of it, but this is the statement that doesn't make this debate pointless or a waste of time. That statement, even though it is true, leads to the conclusion that if a driver keeps his engine's RPM around maximum torque in any given gear, he will get maximum acceleration for the vehicle. And that is not true (except for the 1^st gear, since you cannot downshift further).

So in the debate Torque vs Horsepower, there is one clear winner and it is Horsepower. This doesn't depend on a "feeling", a driving technique or an old wife's tail: It is pure science and undisputable. That's what must come out of this debate.

In this quote:

As you say for any given vehichle speed max acceleration occurs at peak power. But ...

There shouldn't be a 'but'.