Hp vs torque

[gliding_serpent]

This is embarrassing. Or maybe not. I "know all about torque" and hp. I have been quoting numbers from magazines for years. Reciently i have been studying dyno charts to help me choose what i want to do with my car for intake/ exhaust, and because i just geek out on this stuff.

I have seen the math, i have read (internet) articles. What i am still unsure of is the translation of what you see on a dyno to what you feel in real life.

Here is an explanation that keeps things pretty light. https://www.amsperformance.com/resources/technical-articles/56-hp-tq-dyno-chart

What interests me is the statement that the torque curve is identical to the acceleration curve. I thought this in the beginning... Then read some people that refute this concept. The hp curve is calculated from torque.... Would that not be a good representation of power/acceleration? Low torque=low hp = low acceleration and vice versa for any rpm. Steeper curve, greater acceleration as you feel the rate of change faster.

Thiughts? I am a visual guy so i guess this is why i struggle with sll of this. Plus i just don't know who to believe in thus modern internet era of misinfirmation.

http://en.m.wikipedia.org/wiki/Torque

http://en.m.wikipedia.org/wiki/Horsepower

So is the hp or torque curve a better representation of acceleration, or are they both right? Or neither?

[Bill Verburg]

Originally Posted by gliding_serpent

This is embarrassing. Or maybe not. I "know all about torque" and hp. I have been quoting numbers from magazines for years. Reciently i have been studying dyno charts to help me choose what i want to do with my car for intake/ exhaust, and because i just geek out on this stuff.

I have seen the math, i have read (internet) articles. What i am still unsure of is the translation of what you see on a dyno to what you feel in real life.

Here is an explanation that keeps things pretty light. https://www.amsperformance.com/resources/technical-articles/56-hp-tq-dyno-chart

What interests me is the statement that the torque curve is identical to the acceleration curve. I thought this in the beginning... Then read some people that refute this concept. The hp curve is calculated from torque.... Would that not be a good representation of power/acceleration? Low torque=low hp = low acceleration and vice versa for any rpm. Steeper curve, greater acceleration as you feel the rate of change faster.

Thiughts? I am a visual guy so i guess this is why i struggle with sll of this. Plus i just don't know who to believe in thus modern internet era of misinfirmation.

Torque - Wikipedia, the free encyclopedia

Horsepower - Wikipedia, the free encyclopedia

So is the hp or torque curve a better representation of acceleration, or are they both right? Or neither?

The first thing that matters is the torque curve, you want torque at higher rpm for performance, you want torque at low rpm for towing

The torque curve is filtered through the drive train, the trans diff and drive wheels

So you need to look at the net thrust curve to see actual performance feel/potential, you can further refine this approximation of net performance by looking at the predicted acceleration curve w/ weight and aero characteristics factored into the thrust curve data

here are the thrust curves comparing 3 drive train configurationsw/ the same engine

same w/ drag for the same chassis added
added


here is a comparison of the predicted Acceleration curves of a 993 Cup and a 993 GT3RS, the Rs not only have more torque but more torque at higher revs, which makes it much quicker




here a comparison of a l/w E-F series 911 w/ hot rod 3.2 vs a 997 GT3RS the hot rod has as much peak Acceleration potential but only over a narrow range of revs


here is a

[gliding_serpent]

Thanks bill, you are full of good info. I 100% follow those graphs. Do you have the ability to plug data into these graphs?

So then back to my questions, ignoring aero, weight, and drive train loss, is your torque curve a representation of how quickly you can get to speed (accelerate), and hp is how fast you are actually going (with the rate of increase in the hp curve representing the acceleration)? I know that grossly simplifies things.

Interesting discussion here. For those interested, read the comments also
https://danielmiessler.com/study/horsepower/

[gliding_serpent]

Originally Posted by Bill Verburg

here is a

Very cool to see how drag effects the the lower torque 993 cup car more in the higher gears compared to the higher torque 997.

[Tippy]

The broader the torque curve, the longer the useable powerband is.

The reason you "feel" hp while the torque curve falls off (you are really feeling torque), is even though torque is dropping off, it is "adding" up as RPM builds.

Smaller torque events but far more of them.

[haycait911]

in a nutshell.

horsepower sells engines........

torque wins races.

[Bill Douglas]

While on the same subject... What really annoys me while reading spec's on new cars, the always give loads of unimportant data, tell you how many BHP, but never mention the weight. It's rather a waste of time knowing the HP without knowing the weight I feel.

[afterburn 549]

Its been said. But a race engine is uncomfortable on the street . All the pwr is upstairs .
Race cars are just like street cars.. only different ( Laugh right there)

[Bill Verburg]

Originally Posted by gliding_serpent

Thanks bill, you are full of good info. I 100% follow those graphs. Do you have the ability to plug data into these graphs?

So then back to my questions, ignoring aero, weight, and drive train loss, is your torque curve a representation of how quickly you can get to speed (accelerate), and hp is how fast you are actually going (with the rate of increase in the hp curve representing the acceleration)? I know that grossly simplifies things.

Interesting discussion here. For those interested, read the comments also
https://danielmiessler.com/study/horsepower/

Forget hp, it is just a derivative of torque and rpm. If you do the math(I have) the only thing that matters to acceleration is torque, rpm, gearing, aero and weight.

you can't tell much about acceleration from just looking at a torque curve

here are the rear wheel torque curves for 3 993 engines, 2 are mine 1 is a friends


Looking at these curves you can only form the vaguest idea of how the car will act on the road
here is a comparison of my Carrera 3.0 stock vs w/ the 3.6 that is now in it, same chassis and drivetrain


the thrust curves show the gearing effect on the torque curves, since it's all in the same chassis it gives a good indication of the acceleration potential, you don't need aero and weight to get that.

Yes I have a data base of all sorts of things, this area is one that I have been developing as time permits and data sets are added

[chris_seven]

Originally Posted by haycait911

in a nutshell.

horsepower sells engines........

torque wins races.

This old chestnut was attributed to either Caroll Shelby or Enzo Ferrari depending on who you believe.

As a statement this is fundamentally misleading and in absolute terms inaccurate.

Torque and horsepower are simply two sides of the same coin and as already stated you can, to some extent, chose the engine characteristic you prefer.

When it comes to racing then assuming you can correctly gear the car Horspower will always win the acceleration battle.

Torque can best be considered as an engine's ability to do work and horsepower is the rate at which the engine will do that work or use energy.

Looking at dyno plots can be quite misleading if you are comparing different vehicles as they take no account of gearing which is vitally important.

If the difference between peak BHP and Peak Torque is significant in terms of the size of the gap then the engine will generally be tractable but other than that torque curves are quite useless.

By calculating horsepower you gain much more information that can be used to determine performance.

The main thing that really determines acceleration for a given mass is force.

It is the force at the wheels that is important and this is a product of horsepower and gearing using the basic calculation:

Torque = (Horsepower/RPM)X5252

The gear ratio then magnifies the engine torque and it is this product that really accelerates the car.


Optimum acceleration from a given speed occurs when a gear is selected that enables the engine to run at its peak horsepower and not at its peak torque.

High revving, high horsepower engine will be very good in terms of their ability to accelerate a car and why they make great race engines.

Horsepower will, therefore, not only sell cars it will also win races.

I would agree that for many applications low revving, high torque engines can make for very attractive and easy to drive road cars so choosing the characteristics of vehicle is more involved than just looking at dyno curves.

[jeffbottman]

I'm a quant-engineer-nerd type, so kind of like equations. Torque and HP are not independent but are related as follows:

HP = Torque x RPM ÷ 5252 with torque in lb-ft, I think.

Acceleration is proportional to torque, BUT! NOT engine torque, but rather rear wheel torque multiplied by wheel radius. That's why you get much more acceleration in first gear due to the torque multiplying effect of the transmission gear ratio.

Another interesting thing. Suppose you have a continuously variable transmission that keeps the engine at its maximum HP point during hard acceleration. This would yield the absolute minimum time to get to any specific speed. But it would be no fun because the engine would just roar like a motorboat rather than sing that sweet song we love.

[chris_seven]

If you use an IVT then Torque is irrelevant only horsepower matters.

[gliding_serpent]

The way i looked at it (and i am purposefully trying to keep it untechnical) was that torque is the raw ability that an engine produces. Hp is more useful as it takes into account the rate that this ability can be applied based on rpm. Gearing is a huge factor to multiply the hp application in the real world, but assuming all else equal between two cars (i am visualizing upgrades to my car) we can kind of ignore this. Same goes for weight and drag.

Power to weight ratio is another useful number, realizing that it does not factor drag or gearing. But those things being constant (like when i am lightening my car, and increasing power), it is quite useful.

[haycait911]

Originally Posted by chris_seven

This old chestnut was attributed to either Caroll Shelby or Enzo Ferrari depending on who you believe.

As a statement this is fundamentally misleading and in absolute terms inaccurate.

Torque and horsepower are simply two sides of the same coin and as already stated you can, to some extent, chose the engine characteristic you prefer.

When it comes to racing then assuming you can correctly gear the car Horspower will always win the acceleration battle.

Torque can best be considered as an engine's ability to do work and horsepower is the rate at which the engine will do that work or use energy.

Looking at dyno plots can be quite misleading if you are comparing different vehicles as they take no account of gearing which is vitally important.

If the difference between peak BHP and Peak Torque is significant in terms of the size of the gap then the engine will generally be tractable but other than that torque curves are quite useless.

By calculating horsepower you gain much more information that can be used to determine performance.

The main thing that really determines acceleration for a given mass is force.

It is the force at the wheels that is important and this is a product of horsepower and gearing using the basic calculation:

Torque = (Horsepower/RPM)X5252

The gear ratio then magnifies the engine torque and it is this product that really accelerates the car.


Optimum acceleration from a given speed occurs when a gear is selected that enables the engine to run at its peak horsepower and not at its peak torque.

High revving, high horsepower engine will be very good in terms of their ability to accelerate a car and why they make great race engines.

Horsepower will, therefore, not only sell cars it will also win races.

I would agree that for many applications low revving, high torque engines can make for very attractive and easy to drive road cars so choosing the characteristics of vehicle is more involved than just looking at dyno curves.

some good points. I don't race. I drive on the street. I like a motor that pulls, all the time, from anywhere in the RPM range. here's the dyno sheet from my 3.0. also built a 3.4 to similar specs. fantastic 'street' engines. I don't want to be at 5K plus all the time to have fun, plus it pi$$es people off. also I'm lazy and don't want to shift more than I have to.

as you can see, peak HP isn't spectacular and is at a relatively low RPM. but check out the torque 'curve'. gobs of usable torque, all the time. haven't dynoed the 3.4 yet, but went with even 'torquier' cams. floor it at 2K in top gear and it just goes....


ps. +1 on the power to weight ratio. one without the other means nothing.

[Bill Verburg]

Torque is what is measured on a dyno and measured in ft-lb or n-m

HP is derived from torque w/ a little math, ft-lb/sec,

1 ft-lb of torque at 1000rpm(that's where the time comes in) is less HP than 1 ft-lb of torque at 7000rpm, that's why for performance you want torque at higher rpm so that you can use gearing to apply it.

acceleration comes from the wheels pushing the car, push(aka thrust) is measured in lb or n

you get the lbs of thrust by doing a little math w/ ft-lbs of torque and the various gearing steps(cwp(ratio no units), selected gear(ratio no units) and tire od(ft)), ft gets cancelled out in the math resulting in lbs of push(thrust) who cares what the hp is except for bragging rights at Mahogony Ridge

drag is a pull also measured in lb or n

A = net thrust/Mass, you need to use the correct units that are consistent w/ each other to get meaningful results, ie work in mks, Gaussian aka cgs or fps aka British Engineering system

[Cajundaddy]

My oversimplified analogy is that torque gets me out of the corners and hp gets me down the straight. A broader torque curve will yield more gear choices while a more vertical torque curve hits you with that punch we associate with a turbo coming on boost.

[VFR750]

Bill,

As always, very informative. Love the thrust-drag, w/gearing curves. Easily explans why a car feels like it hits the wall at speed. Mine, ~120mph. Just runs out of torque to fight the drag. No much "A" left over. I need tracks with shorter straights to negate big HP cars. Maybe some rain too.

[Bill Verburg]

Originally Posted by VFR750

Bill,

As always, very informative. Love the thrust-drag, w/gearing curves. Easily explans why a car feels like it hits the wall at speed. Mine, ~120mph. Just runs out of torque to fight the drag. No much "A" left over. I need tracks with shorter straights to negate big HP cars. Maybe some rain too.

Here a very healthy, Ct valley cheater motor, 3.0SC f/r wings, 3000#s w/ driver, 275/35 x15 tires

[Bill Verburg]

here is one showing the hp and thrust curves, to me the hp curve is useless, the thrust curve gives you a glimmer of the cars potential

[VFR750]

What's also interesting is how the torque curve changes your approach to shifting

In your 3.0 plot, ideal for 1st - 3rd is to shift at redline. 4th is where ringing it out is worse than going to 5th. Just have to account for shift time to decide what's better.