Ive seen many posts about cars having much more torque than hsp. Also some that were pretty close to even. Whats the relationship between the two and which way would make a stronger engine thru the entire rpm range.----more hsp than torque or more torque than hsp

 

I have allways heard it said: Torque will get you out front and horsepower will keep you there.

 

All engines make more torque than horsepower...below 5252 rpm.
(Horsepower is calculated, based on torque and rpm, and the lines always cross {hp will equal torque} at 5252 rpm.)
An engine that makes more PEAK hp than PEAK torque is a very high rpm motor. Don't let anyone fool you; it takes torque AND rpm (i.e. horsepower) to accelerate a vehicle rapidly.
Look at it this way; you could have a powerplant that develops 1000ft/lbs of torque at zero rpm but it won't accelerate anything at zero rpm. (aka zero horsepower)

Accelleration is based on: How much work can your engine do (torque) and how fast can it do it(rpm/horsepower)?
You don't see many ProStockers shifting at 4800rpm, do you?

Larry
code5coupe

 

Torque is loosely a measure of force applied, horsepower is loosely a measure of the ability to do work, the rate at which work is done, etc.

They are related by the following mathematical equation

Horsepower = (Torque*RPM)/5250

Therefore if you know torque at a given RPM, you can calculate horsepower and vice versa. Likewise if you know the torque and horsepower you can calculate the RPM. So long as you only have one unknown you're gravy.

A very important note is that at 5250 RPM's you're left simply with the equation Torque = Horsepower. EVERY vehicle makes the the same numerical value for torque as it does for horsepower at 5250 RPM's. If it does the data is either flawed or if you're looking at a graph, they are not plotted on the same scale.

Which is better? If car A has higher torque than car B at a given RPM it MUST have higher horsepower than car B at that RPM.

I think you're get at something like if you have a car that makes 400 pounds of torque and 200 horsepower vs a car that makes 200 horsepower and 400 pounds of torque and you want to know which is faster right?

If the race is long enough, higher horsepower will win every time, because remember, higher horsepower at an RPM automatically means higher torque at an RPM. Given a short race though where the engines might not be allowed to operate at their maximum power ratings, you have to look at the area under the horsepower curve for the range in which the engine is operated during the race. The car with the higher area under the curve, PROVIDED EVERYTHING ELSE IS HELD CONSTANT, will be faster.

 

Our L-98's are a good example of high torque/moderate HP. The cars have very fast low end acceleration, but fizzle out at about 4600rpms due primarily to limited airflow through the long tube runners and manifold. I think I read where the TPI was originally designed for a 305 to move a station wagon. High rpms was not an issue.

The trick is trying to maintain a good low end torque signature but increasing the higher rpm curve. This gets done by shifting the torque curve "to the right." As a practical matter we do this with cams, heads, better induction etc. Result is the engine's ability to process more air/fuel mixture at higher rpms. The formula's above demonstrate the mathematical relationships of torque at higher rpms makes more HP.

But with enough of that "shifting to the right" we can destroy an engines street manners by not leaving enough torque to move the car at low rpm's. We end up with a race car that must be launched at high rpms where it is back in its torque curve or risk falling on its face while trying to move from a stand still. The myriad of good alternatives available within the SBC framework, for example, from 265 cu inches to 434 and beyond, reflect the bewildering array of alternatives of shifting the torque signatue all over the boards. So "which is better" depends upon what you want to accomplish.

 

Believe it or not though there are some mods that do not require shifting the curve any direction but up. When I installed my 1.7 rockers I gained power at EVERY point. Such mods are rare, but awesome when you do find them. Forced induction would be a another example, although very costly. It will decrease your low end a little because of the extra drag, but it certainly won't require a drag strip launch. A turbo does the same but the loss in low end would be miniscule.

 

Here's a relationship to consider:
1) Torque = Force * Distance
2) Force = Mass * Acceleration
So your acceleration is directly tied to your torque, but also to this "Distance" which is your gear ratio.

For example lets compare the L98 corvettes with the Honda S2000.

They both have ~240 HP, they both run 14.0 in the 1/4.

The corvette has almost twice the torque (345 vs 153 ftlbs) but it also weights 500 lbs more. The s2k at peak hp (7500 rpm)is over double the RPM of the vette (3200 rpm).

You see, the advantages cancel out, the vette has twice the torque but the sk2 has twice the rpm, therefore by gearing the s2k down you can multiply that puny 153 ft*lbs to pull the same at the tires as the corvette's 340 ft*lbs, but you go through the available RPMs that much faster (which is ok becase it has twice the RPM to use).

Hence the phrase "Torque area under the curve". Generally a transmission will be tuned to the powerband of the car from the factory to take advantage of this curve.


HP is the determining factor in top speed. But keep in mind, if you can't produce the RPM needed for peak HP at a certain speed you're finished, even if you have more room on the tach (this is where a lower gear ratio would come in handy).

 

Your stipulation about thru the entire rpm range leads to some basic concepts that always gets lost in these discussions.......

First as has been stated torque and horsepower are related to each other mathematically by rpm........

So the other factor is gearing....which leads to what the rpm range will be....The ideal gearing/transmission for maximum acceleration would be a continously variable transmission that keeps the engine at the rpm which produces the peak horsepower........

Bottom line horsepower is the most important, but you have to have gears to use it.......and practically you need a broad torque curve to maximize the "area under the curve"...

Practically speaking a high horsepower engine that is not too peaky, ie broad torque curve, will give best results..

Whew!!!!

 

therefore by gearing the s2k down you can multiply that puny 153 ft*lbs to pull the same at the tires as the corvette's 340 ft*lbs,

Somehow it just ain't fair!

 

Neither. Either. Both. They are inseparable. If you make more torque at a given rpm, by definition, you have more horsepower at that rpm, also. The formula given above (and here, also) shows the relationship.

HP = [Tq × rpms] ÷ 5252

Torque is a REAL thing. It is a force. We measure it by man defined terms, such as feet and pounds but it is a raw force. Horsepower is a man made measure of the ability to do work. James Watt observed a couple of draft horses at work and defined "horsepower" as a means of comparing the ability of his steam engine to accomplish a task, to a known entity, the horse. In short, torque is a raw force which may or may not cause motion. Horsepower is a man made measure of the ability to produce work, which by definition, DOES require motion.

Which is more important? They are inseparable.

RACE ON!!!

 

I'm going to test you guys a bit..

question..
Where does the 5252 come from??


I'll derive it if anyone is interested..

Heres a hint.. Power = torque * angular speed (rad/sec)

 

Alvin:

DON'T ASK QUESTIONS. This is the internet - everything you read is true, factual and should be accepted blindly without hesitation.

 

Correct me if I'm wrong but you're just looking for a glorified and annoying unit conversion

I had a mechanical design class last semester that did a section on gear trains. They gave this three page explanation of how to calculate power based off of the velocity and the transmitted load, blah, blah, blah. If you were to be designing shafts and such it would come in handy to calculate those loads, etc. The equations given had everything in terms of kN and kW. On test day though the question was quite simple, none of the forces on the shafts mattered, the only thing was important was horsepower, torque and RPM AND to make it better it was given in units of something real easy to convert like in-lbs. Everybody in the class worked on that problem for 45 minutes, I was done in 5 because I knew my equation of HP = (TQ*RPM)/5250 (5252 if you're picky). That equation isn't anywhere in the book but it works perfectly and saves so much time it's not even funny.

Edit - I decided I'd pull out that old test and see just exactly what the question was and I can't find the damn thing. I can find everything else related to the class, but not the test. It's particularly annoying because I never throw anything away. I know we had to send him our first test back with our final design project, but I should still have the second one. Oh well.

 

What.. the units that put the man on the moon aren't good enough for you!!






Yeah, its just a units converstion from Rad/sec to RPM then figure in 550 ft lbf/sec = a HP. I was just asking to make sure that someone doesn't think 5252 really means anything significant... I was on a Fbody site and they where talking about how it means the dyno is calibrated or something kinda dumb like that and I just thought to myself.. humm.. I wonder if anyone actually knows where it comes from..

Power = torque * omega is a pretty powerful tool in alot of electrical problems.

 

Hey I'll work with any units you want, but when you give me a problem in one set of units and want an answer in a similar set of units and I can do it directly without having to convert to something completely different, that's certainly the route I'm gonna take.

 

I'm just playing with you... Thats what a old professor I had woudl tell us when we would bitch about weird english units showing up on test.

 

Seems to me everyone is dancing around the answer, but not quite getting there...

First everything you have stated is absolutely true........now comes the big but......there are gears involved too......and the "shape" of the torque/horsepower curves....

torque at the rear wheels is what makes the car accelerate.....to reiterate my previous post you are putting the maximum torque at the rear wheels when the gearing is such that the motor is producing it's maximum horsepower.......

So the discussion of is horsepower or torque more important doesn't fully address the issues of getting maximum acceleration......you have to factor in gears also......think about a close ratio 4-speed vs a wider ratio......keeps the engine at or near peak horsepower, even if the torque curve were perfectly flat....

 

I can get very deep into this if necessary but dont really want to explain every detail because I dont have all night.... but to nitpick just a bit since I am a physicist....torque is NOT force, nor is it power. It can be loosely thought of as being either, but be sure to say that instead of presenting it as fact. Someone who knows what it is might think you are stupid. When I try to explain it to students I'm tutoring, I start by letting them imagine a 'twisting force' before taking them further.

N (torque) = r x F, which is a lever arm multiplied as a cross product by a force. When you use a cross product, it means the number itself is multiplied together, but you have different directions associated with each term, so that the resulting torque direction is perpendicular to both of the other 2. It is NOT simply F*distance, that is called work and has no direction assigned to it.

Just a simple example of what it is because it is its own concept which can be tough to grasp, open your front door and close it by pressing on the ****.....then reopen it and try to close it by pressing close to the hinge of the door. The distance between where you press and the hinge is the lever arm (r, a distance) and the amount of force needed changes when you shorten that distance as you will see.

Now to answer the original question, as has been said its just a mathematical relationship between the two. I try to think of torque as what gets me going and that HP just gets me that top-end speed, but that is not exactly right, I just dont care to write a full essay. For most intents and purposes though, that will suffice nearly everyone.

 

That's why I said "loosely" Torque is a calculated value which depends on force applied and lever arm distance. If you zero either, you have zero torque. I say that it can be "loosely" considered a force though if you throw in there that it is a force IN A RADIAL DIRECTION. Nowhere though in the torque equation does time enter, hence horsepower, or loosely, how quickly can that torque be applied?

I think most people fully understand the difference (or it's not really relevant to them either way), it's just a matter of trying to explain it without having to write the entire essay. You know as well as I do that when you try to be as thorough as possible, people just tune out. Sometime's it's better to stick to the quick and dirty answers.

For what it's worth I understand where you're coming from though.
I've grown up with electricity so it just absolutely kills me when someday says I'm going to "ohm it out" or "how many volts does it take to kill a person" You can't "ohm" anything, but you can certainly measure the resistance. Voltage doesn't kill, but current certainly will. I actually had a good friend of mine ask me "how many amps can you get out of regular electrical socket?" My answer was "how many do you want?" He made no mention of how long we wanted to be able to sustain said current flow. If he asked me how much current a standard electrical outlet is rated for, that would have made sense and I could have told him anywhere from 10-15 amps depending on the quality. As he worded it though the proper answer was nearly infinite.

 

Interesting discussion going on here.

If I have a heavy street car like a C4 or heavier I will focus more on building torque than horsepower every time. Big horsepower typically requires a loose converter and a lower gear ratio to allow you to take advantage of the operating range otherwise it is tough to get the car moving. An engine that focuses on torque will have much better street manners than an engine that focuses strictly on horsepower. John Lingenfelter has written tremendous articles and he even wrote a book on this exact subject and torque generally is the winner for the street.