Torque vs. HP Revisted

[bobcowan]

Originally Posted by ERA Chas

Bob-you quote me twice in your post and I essentially agree with everything you write. What you missed was my point to OP that torque overcoming grip in a Cobra is a. not beneficial, and, b. easier to do than say a DP or Rolex Sports Car.

That is very true. Torque that overcomes grip in any vehicle is not very useful. And, you're right, in a light weigh car it's easier to overcome available grip - especially at low speeds.

There's no such thing as too much power, only not enough control.

Control means setting up your suspension correctly, and proper management of your right foot.

[AL427SBF]

Originally Posted by bobcowan

Depends on what you mean by "maxiumum", and the application. I'm making a lot of torque, across a broad range. As long as the track is dry, I'm always looking for more torque.

There's no such thing as too much power, only not enough control.



Not at High Plains Raceway! Turn 3 opens out on to a long down hill back stretch.



Not true. Every time you come out of a corner, you need all the torque you can get. You're not starting out from 0, but you're often coming from 60 and heading for 150.

Since I have a lot of torque everywhere, I don't have to shift much. I use 3rd and 4th only. Every time you shift you lose time, and have the potential to upset the car. And it gives you more things to do while you're already pretty busy.

I'v ridden in other cars that don't have as much torque, and have to work harder to keep the engine in it's power band. There's often a lot of shifting going on. That's especially difficult when pulling a steep hill.

Actually, this quote came from ERA Chas ...
Since you now define road course use, build for HP. You only leave from rest once there.

My reply is in sync with you ...
Actually, anytime I want to accelerate I will be calling on torque, all gears over a broad RPM range.

[patrickt]

Originally Posted by AL427SBF

Actually, anytime I want to accelerate I will be calling on torque, all gears over a broad RPM range.

Sooooo, I guess you're fed up with your small block, huh?

[ERA Chas]

Originally Posted by patrickt

Sooooo, I guess you're fed up with your small block, huh?

If you take this bait the smart guys will cease contributing to the discussion....

[patrickt]

Originally Posted by ERA Chas

If you take this bait the smart guys will cease contributing to the discussion....

[AL427SBF]

Originally Posted by ERA Chas

If you take this bait the smart guys will cease contributing to the discussion....

The discussion was over when Bob and a few other smart guys confirmed what I sort of thought, torque is king, tune for a big flat one

[olddog]

Torque is the rotational equivalent to linear force.

Hp is a measure of the rotational equivalent to linear work.

You can put 400 lb-ft of torque on a stuck bolt, but until the bolt turns you have done no work on the bolt.


So yes, torque is the force that moves the car, but Hp is the measure of the work that is done on the car.

An engine turning 8000 rpm with 200 lb-ft of torque makes the same power as an engine turning 4000 rpm with 400 lb-ft of torque. If both engines are geared to go the same speed at their respective rpm, both engines will accelerate the car at the exact same rate, assuming the same drive train efficiency and car (weight).

If torque was the only thing that mattered, race cars would have diesels in them.

[olddog]

Originally Posted by AL427SBF

Sort of gets back to the original proposition, maybe were talking past each other. Don't need to build for 600+ HP, need to build for the broadest torque curve the motor will support, HP will fall in-place as a derived result.

Since you now define road course use, build for HP. You only leave from rest once there.

Actually, anytime I want to accelerate I will be calling on torque, all gears over a broad RPM range. Ohm's law analogy ...

V=RI
Torque = Current (I)
HP = Volts (V)
Motor Efficiency = Resistance (R)

High Voltage without Current, will power nothing
High Resistance without Current, will power nothing
High Current, regardless of Voltage or Resistance, will kill your ass

In electricity:
Watts is the measurement of work where 746 Watts = 1 Hp
Watts = Voltage * Current

Voltage can be thought of as the pressure that pushes current through a resistance. It takes 1 volt to push 1 ampere of current through 1 ohm of resistance -- Ohms law.

Resistance should not be thought of as being equivalent to efficiency.

The above is true for Direct Current (DC). AC gets more complicated as power factor comes into play.

[AL427SBF]

If torque was the only thing that mattered, race cars would have diesels in them.

You better let Audi and Peugeot know so they can retool their Le Mans entries.

[patrickt]

Originally Posted by olddog

In electricity:
Watts is the measurement of work where 746 Watts = 1 Hp
Watts = Voltage * Current

Voltage can be thought of as the pressure that pushes current through a resistance. It takes 1 volt to push 1 ampere of current through 1 ohm of resistance -- Ohms law.

Resistance should not be thought of as being equivalent to efficiency.

The above is true for Direct Current (DC). AC gets more complicated as power factor comes into play.

I tried to bait ol' Chas down this path last month. But that fox was just too sly (see my post below). Now, with Al, I'm not so sure....

[olddog]

Originally Posted by AL427SBF

If torque was the only thing that mattered, race cars would have diesels in them.

You better let Audi and Peugeot know so they can retool their Le Mans entries.

Let me amend that. If torque was the only thing that mattered, all race cars would have always had diesels, including the Cobra.

Picking the rare exceptions to the norm to make a point, does not make the norm wrong.

Technology changes. Today's diesels can turn more rpm and we can make them lighter. You can bet your ass these diesels are making very similar Hp to the gasoline engines they compete against, regardless of what rpm they turn. Otherwise, they wouldn't be competitive.

But for the record, I like a nice flat torque curve. High rpm engines tend to break sooner and more catastrophically. Life is a balancing act.

[scottj]

I have a question... is it believed that building for high HP means having a narrow, peaky, torque curve? Because, that is simply not true. I can show you dyno sheets for 9000 rpm race engines that are flat over a 3000+ rpm spread. Every performance engine I've ever owned was developed to have the widest, flattest, torque curve possible.

The real question being discussed in this thread is, what is the best rpm range for this application? Once the rpm range has been determined, saying, "tune for a big flat torque curve" is stating the obvious.

Of the 4 engines I've had in my Cobras, I've always built them for max power in the 3-6000 rpm range... because I drove them on the street as well as the track. An frankly, the power we made in that rpm range was probably more than my average skills could use anyway.

[AL427SBF]

From the kick-off post ...

If we agree that torque is what moves you (acceleration), and HP is what keeps you there (speed) then it seems to me Torque is king and all efforts go to giving you the most torque relatively early in the RPM range (say @ 3K) and holding strong (flat or better) for as long as possible past the RPM range of 5252 ...

... if you have maximized your torque curve in that way, who cares about peak HP in a practical sense.

You will always get your "HP", HP = TORQUE X RPM / 5252, it's just that for engine building & tuning purposes, no need to pay attention to HP, let it fall out from the optimized torque band.

[Jerry Clayton]

Of all my stuff, have never had one on a dyno--------------

[RET_COP]

Scottj is right on. I may have read the OP wrong, I was thinking of mostly competition and had to revise my thinking for the street, other posters made good sense also...But the OP did say "no need to pay attention to HP" and that I don't agree with. But I do understand that a flat torque curve is a good thing.
Lou

[AL427SBF]

Maybe a little narrow on applicability, street yes - and any road course competition. Bob said it best -


Every time you come out of a corner, you need all the torque you can get. You're not starting out from 0, but you're often coming from 60 and heading for 150.

Since I have a lot of torque everywhere, I don't have to shift much. I use 3rd and 4th only. Every time you shift you lose time, and have the potential to upset the car. And it gives you more things to do while you're already pretty busy.


If you understand HP is just a number crunch on torque and a derived value from it, then you would understand why "no need to pay attention to HP".


CompCams axiom "build for torque and the horsepower will take care of itself"

[lovehamr]

Sounds to me like Olddog, Tommy and Scottj are the only ones with really a firm grasp on this. Every now and then someone pops up with that same argument and truth be told we'd probably all be better off using the aussie's expressions in watts. But since that wasn't really on the table, lets look at the euphemisms vs. math thing again. Some of this has already been covered but lets go a little deeper.

These are misnomers;
“You feel torque from the seat of your pants much more than you feel horsepower."
"Torque gets you off the corner."
"Torque is more important that HP."

The human butt can no more distinguish torque from HP than it can blue light from red light. In simplest terms we are dealing with power or energy, a force that moves you. These forces are expressed in mathematical terms thusly;

1 HP = 33,000 foot-pounds per minute
Or it could be P/hp=[T/(ft lb)][w/(r/min)] over 5252
By the way, that 5252 is why all dyno charts show the HP and torque curves crossing at that RPM.
Or it could be 746 watts
Or maybe 2,545 BTUs (British thermal units)
One BTU being equal to 1,055 joules, or 252 gram-calories or 0.252 food calories.
This means that 1 HP is also equal to 2684975 joules, or 63504 gram-calories, or 641.34 food calories
Presumably, a horse producing 1 horsepower would burn about 641 Calories in one hour if it were 100% efficient.
The point is that its energy, a force, what moves you, not some nebulous calculation.

Torque is the force applied to a lever, multiplied by its distance from the lever's fulcrum in our case a theoretical lever and a rotating fulcrum, or more simply:
T = r x F (whadaya know another calculated theoretical number)
Which is linier force multiplied by a radius. Of course this formula always assumes a perpendicular force axis to the fulcrum.

To put this into perspective the next time you want to accelerate really fast try shifting at your engine’s torque peak (for many of us it's around 3500 rpm) rather than the HP peak (say 5800 rpm or maybe even 7000 if you have a lot of race kit). It doesn’t take a rocket scientist figure out using which shift point will accelerate the vehicle faster. This is because we’re talking about energy expended over time not a static applied force. To say that another way; I could put 84 pounds (that’s my Buell's peak output) of torque on your MC crank shaft with a ratchet handle, but I don’t think you’re going to accelerate too quickly and I doubt that you’d feel it too much in the seat of your pants either.

Suffice to say that your engine is a pump and the faster that it can turn and make power within the constraints of VE then the faster you're going to go regardless of whether you measure that output in torque, HP, watts, joules, calories, BTUs or warp factors.

Steve

[scottj]

A vehicle in motion has kinetic energy.

Acceleration causes a change in kinetic energy.

Power is the derivative of energy, which is to say, power = the rate of change of energy.

To increase power is to increase the roc of energy.

An increase in the roc of energy is increased acceleration.

Therefore, an increase in power causes an increase in acceleration.

Understand horsepower and its relationship to torque and you will understand that the higher the average horsepower, the higher the rate of acceleration… whether or not “you need to pay attention to HP” is up to you…

[Jaydee]

You can multiply torque with gearing, but you can't multiply HP. The higher the gear ratio, the higher the torque.
JD

[fordracing65]

Just try to get 600hp and 600ftpds torque by 6000rpm's and you will be fine...