torque versus hp
read this it will help
http://www.vettenet.org/torquehp.html http://ryanscarpage.50megs.com/street.html

 

good reading, thanks.

Jim

 

Interesting treatment, thanks for the info.

May I conclude that the shift point (in a 1/4mi run) should be chosen such that the torque after the shift (gearing considered) is the same as before the shift? Though of course it was decreasing just before and increasing just after the shift.

For example my A4 produces almost a 50% drop in torque to the rear wheels after the 1-2 shift. So I would shift at the point where torque had fallen to 1/2 of where it will be after the shift, actually slightly before that point due to shift lag.

I had been looking to maximize the area under the HP curve, but looks like I should be maximizing area under the torque curve.

Do I have the correct grasp of the concept here?

 

NO! ideally you should shift at the rpm point that drops you back to your torque PEAK that normally just past your hp peak but of course varies in each shift due to the transmision gearing this will in most cases move the car faster! heres the common gear spreads in G.M.transmisions, http://www.geocities.com/z28esser/ratio.html
so if you have a 23% ratio drop from 1st to second your rpms will need to be 23% above the torque peak rpms when you shift from 1st to second gear, but keep in mind if that rpm is well past your hp peak or is approching your engines redline you need to use common sence and shift earlier in the rpm range and fall back to just below the torque peak, blowing an engine is not worth the couple of 100drths of a second a higher shift point MIGHT GIVE YOU.


[Modified by grumpyvette, 12:34 PM 3/26/2002]

 

Match the cam with the heads!!!! dont put a monster cam in your car and say "but there corvette heads they must want more cam" just remeber Torque gets you there horspower keeps you there.

 

Very interesting. I feel like the first article is more thought out than the second one.

The second article seems to ignore that a lot of low end grunt can get you a big leap at the light. Now granted you won't keep that lead unless you continue to make torque in the higher RPM's. Low end torque is a good thing, but it needs to continue as well. He claims torque doesn't win races, I have to disagree. If he has a motor that makes hella low end torque but none at 6000 rpm's, yeah he's dead. Now if you take a motor that makes hella low end torque AND makes good torque at 6000 rpms, such as the broad curve of the LT1, you're gonna do good.

If nothing else he needs to re title his article. Torque doesn't lose on the street, a lack of high end torque loses on the street.

 

65Z01, you had it right the first time: maximize area under the HP curve. period.

(a million posts and websites still can't change physics!)

 

What a bunch of horse-hockey. Torque is the ability to do work. Horsepower is the rate of doing work. Torque is independant of time. 1 foot pound of torque will raise a 1 pound weight 1 foot. It doesn't matter if its done in 1 minute or 1 year, the same amount of work has occurred. Horsepower on the other hand, is time dependant. 1 horsepower will raise 550 pounds 1 foot in 1 second. 10 horsepower will raise the same 550 pound weight the same 1 foot in 0.1 sec. Note that the same amount of work has been done, the 550 pound weight in each case was raised 1 foot.

It's not torque that accelerates cars. Its horsepower. Now, cars with lots of low-end torque also have low-end horsepower. So people talk about how torque is what gets you going. Not true. Its the horsepower that accelerates the car. And since its the horsepower that causes acceleration, you want to maximize the "area under the curve" for horsepower, not torque. For most engines, this is approximated by shifting at the point on the curve past the horsepower peak where the horsepower before the shift equals the horsepower after the shift.

 

I'm sorry but horsepower is a number that somebody made up off of torque. It's all in the math. Horsepower is a representation of something that doesn't really exist. It basically says that to make horsepower you have to have a lot of high end torque, or the motor has to turn a lot of revs.

I don't put any stock in horsepower numbers, look at a dyno graph and look at the area. A high horsepower motor might not be able to accelerate worth a crap. Torque is a FORCE and the acceleration formula uses FORCE in it's equation. Sure, a motor that turns 10000 rpms might have nice horsepower numbers, but without torque, how long does it take to get to that 10000 rpms? Horsepower is a purely made up nice number to talk about, but without torque, have a nice day.

 

Yes, the acceleration formula uses force, but it also has a time function to it. Torque does not have a time component, but horsepower does. Think of it this way, torque is the amount of force needed to move an object. Horsepower is how fast the object is moved. Torque will provide the force needed to move a car 100 mph, but horsepower is what accelerates you to 100 mph in 14 seconds. If you want to get to 100 mph quicker, you need more horsepower. You can get more horsepower by increasing the torque at the same rpm, or increase the rpms using the same torque. or some combination of the two.

If you believe that torque is what its all about, then I guess the Formula 1 teams have it all wrong. Their little 200 lb-ft, 18,000+ rpm buzz bomb engines with 800 horsepower will never be able to accelerate the cars like they do.

 

nathan, you're incorrect that horsepower is an imaginary measure. in fact, a dynojet measures hp (work over time, or how quickly the mass of the drums is accelerated). it then uses hp, along with the RPM it measured, to calculate torque. (if you leave the inductive pickup off, so no rpm, you get a graph of hp vs speed.) this is precisely how the dynojet gives you engine torque numbers. it knows the wheel speed 'cause it knows how fast the rollers are turning, and it knows the rpm, so it can calculate overall gearing.

otherwise, all it could tell you is wheel torque, which won't tell you squat about how much torque the engine makes unless you know all of the ratios involved.

i'll try to put it another way... as you wind through a gear, you get to the rpm point where torque starts dropping. but, since torque is multiplied through the drivetrain, the effective torque at the wheels (a multiple of the gear ratio) is still higher with less engine torque than if you shifted up. that is, if you shifted right when the torque dropped, now your torque at the wheels has lost the multiplication of one gear to the next, and you're accelerating significantly less than just before you shifted.

hp is precisely a measure that overcomes gearing changes. this makes it the real-world measure. that is, if you follow the power curve of an engine, you end up precisely maximizing the torque _to_the_wheels_. 250ft-lb at 6k rpm through a 2.6 gear is more torque to the wheels than 310ft-lb at 4k rpm in a 1.8 gear, in other words.

so, in a sense you're correct, maximizing torque is going to maximize overall acceleration. but, torque at the flywheel is irrelevant, unless you use it in a set of equations that take everything else into account. this is the beauty of power, it's real, and it bypasses all of the little things to tell you what's really going to happen.

experiment: at the dragstrip, make a run shifting at 4k. then make a run shifting at 6k.

 

You can't deny the importance of torque, you just proved it yourself again. Yes a 200 pound of torque 800 horsepower motor does that because it turns so quickly. Cut that torque number down to 10 instead of 200 and see how many revs you have to turn to get the same number. Horsepower is built from 2 things, torque and RPMS. In the case of a chevy V-8 which is what most of us have, it's easier to add torque than it is to add RPMS, thus torque is very much important. Sure horsepower might be a good number to try and put it in perspective, but if you hold everything else constant.

2 motors, both can only rev a max of 6000 rpms, the one with more torque is faster, period. Yes you can say HP is a factor, but being that it's a function of torque, it's really useless. In this situation, no torque = no HP. If you can figure out a way to cheat the formula and make a 0-6000 rpm motor with no torque make 1000 hp, I'd like to see it. That'll be some kind of new math.

You want to talk about high revving indy cars, go for it, apples to oranges is all you will find.

 

BTW, saying HP was an imaginary number I suppose is a bad choice of words. Anyway, I've always heard it as torque gets you moving and HP keeps you moving.

Torque at the begining of the track, HP at the end.

That being said you absolutely cannot have one without having some of the other. If torque is the whole story than big diesels will win races, if hp is the whole story then high strung ricers will win races. The problem is that neither tend to win very much of anything. That leads us to believe that you have to have both. More torque = more HP for any given RPM, period, amen. Saying you have a lot of HP and that torque plays no part is ignoring the real picture, so is saying that you have a lot of torque and HP plays no part.

I'm just trying to say that because HP is calculated off of torque, it's impossible to have high HP without having high torque (given the SBC rev range) So we don't need to confuse the issue. A v-8 tells me he makes 300 hp, to me that's more impressive than a ricer that tells me he makes the same 300 hp. I know this because I know that the v-8 makes enough torque to get him going while the ricer doesn't really. You have to be able to visualize the torque curve to get the real picture.

For example if we have 2 cars that are identical, they both make the same HP, but one makes more torque, traction issues aside, the one with more torque wins.

Conversly if you have 2 cars that are identical, they both make the same torque, then the one with more HP will win (obviously he can rev faster which HP ignored simply means he can maintain the torque multiplication of his lower gears longer)

Anything not make sense? I'm trying to remove all the hype and BS to try and look at the real picture. Afterall a picture says a 1000 words. :cheers:

 

i wanna say this is a case of semantics, but i'm not perfectly sure it is...

technically, what wins races is the time spent under the hp curve. what i think you're saying is that an engine that makes a lot of torque everywhere is very fast. absolutely. even if this engine's peak hp is less than the proverbial small, peaky engine, the area under the power curve for its rpm range may well be more.

but, the stickler is that, mathematically, in the real world, no matter how you slice and dice it, what tells you which engine is faster it simply the area under the power curve. if you integrate the torque curve, it won't tell you enough to decide.

obviously, more area under the power curve means the the torque curve is also meatier. of course, they're forever linked mathematically such that one can't change without the other. my point is that looking at the torque curve tells you a part of the story. looking at the power curve tells you how fast the car will accelerate over time.

in your example of 2 identical cars, but one with more torque, that doesn't make sense. 'cause the one with more torque also has more power under the curve.

but, now take 2 cars with identical torque curves, but shifted in the rpm range (one makes 400ft-lb at 3k rpm, the other at 5k rpm, and if you shifted the curves they'd fit over each other perfectly, such that the area underneath them is identical). keep them both so they're spending the exact same amount of time over the same engine torque range. the one with more power wins. why? because it has to have shorter gearing in order to maintain the same engine torque value, and the same engine torque value with shorter gearing translates to more torque at the wheels.

but, looking at these 2 torque curves in comparison, nothing tells you which one is faster, unless you know the relationship between hp, torque, and rpm, and you see the rpm axis. on the other hand, if you plotted these 2 engines in hp, the difference would immediately be obvious.

i didn't mean to imply anything about peak numbers.

 

"My approach has always been to maximize torque for street-driven engines, which means avoiding the large cross cross-sectional area cyclinder heads in favor of smaller intake runner cylinder heads with excellent flow numbers." then theres this offering "Camshaft design must also be intergrated with the cylinderheads, Intake,and exhaust systems. Since camshafts are relatively inexpensive compared to cylinder heads and other internal engine pieces, enthusiasts often go overboard in camshaft selection. Suffering from the "bigger is better" syndrome." then theres "I have built a number of these engines using the ACCELL super ram electronic fuel injection intake I designed. This combination of cubic inches and intake manifold creates outstanding torque. One roller cam 420 with ported Air Flow Research heads generated 407 lbs-ft. of torque at 1600RPM. this engine also cranked out 542 lbs-ft. of torque at 4500RPM and 525HP at 5500RPM! thoes are rat motor numbers from a 11:1 small-block." These excerpts are from a book written bu Mr. John Lingefelter Horsepower is Torque over time If you start with more torque Its alot eayser to make Horsepower. Thats just simple math. An engine is an airpump the more air you can pump thru it the more power you can make. The problem lies in the fact that if you hogg out the heads on your car your driveability suffers because the heads can only make power further up the power curve John beleves in port velocity to build gobbs of torque you can use in A STREET ENGINE. Now multiply lots of torque at a lower RPM to make the same horsepower as a highly strung engine with little torque presto A great street engine!!!!!!

 

HP is the only thing that matters when evaluating the basic acceleration potential for any vehicle. It a power to weight consideration and nothing else. A man riding a bike has a tremendous torque to weight ratio when in the lower gears and yet can't even outrun a regular car.

With appropriate gearing even a man can generate millions of foot opounds of tq. No amount of gearing can raise horsepower however because it's fixed by the amount of fuel and air being consumed and converted into work per unit time and not gearing related like the simple static force, torque, is. A mouse can exert a million foot pounds of force through the right levers or gears yet has no power. With the right leverage he can move a train but it might take a hundred years!

 

Sigh.

Take a 300 hp, 1 pound of torque motor. Sure might make plenty of power, but it has to turn 1575600 RPM's

Make 100 pounds of torque and the same 300 hp is obtained at 15756 RPM's

Make 300 pounds of torque and the same 300 hp is obtained at 5252 RPM's

Now tell me torque isn't important? I'm just trying to illustrate the point that horsepower is a CALCULATION, derived from RPM and TORQUE. If you know both RPM and TORQUE, you can draw your own conclusions in your head without needing the actual HP number precalculated for you. Sure it's a nice number to have, but looking at HP numbers alone is not looking at the total picture.


[Modified by Nathan Plemons, 7:19 AM 3/27/2002]

 

Now that the rest of us are now confused, I must add that both the torque numbers and the hp numbers are significant. You must use both to maximize the formulas to determine gearing and shifting reccomendations for a faster elapsed time. You have to remember that there are alot of other factors that affect the determination of what point in the rpm scale to shift at. :confused:

 

[QUOTE]nathan, you're incorrect that horsepower is an imaginary measure. in fact, a dynojet measures hp (work over time, or how quickly the mass of the drums is accelerated). it then uses hp, along with the RPM it measured,
[/SNIP]


Whether you call HP imaginary or calculated doesn't really matter; just a play on words to me, meaning the same thing.

It's really news to me that a DynoJet works that way because it's always been just the other way 'round. As with any three factor mathmatical formula, if you two of them you can calculate the third.

Torque is what's measured and horsepower is what's calculated. All you have to do is to look at the formula, torque x RPM/5252. You'll always see the formula written that way.

Without getting into a long discussion on this, HP is simply the engine's ability to make torque at a certain RPM (time). It's a measurement of work done. A given amount of torque made at a higher RPM will result in a calculated higher HP number.

Do the math: Take 300 lb/ft or torque at 800 RPM and then take that same amount of torque, but this time at 5000 RPM - Big difference in HP numbers, but still the same amount of torque.

I thought the most folks knew that torque is what the dyno actually measures and from that the dyno calculates the horsepower based on the formula. Horsepower and torque will always cross at 5252, which is the mathmatical constant in the equation, which I understand was an arbitray number selected back on day one.

I still maintain that torque can exist without HP, but HP cannot exist without torque.

The water, etc. brake (for an engine dyno) or roller (for a chassis dyno) is actually applying a load which the engine/tires must overcome. The engine's ability to overcome that load determines the engines ability to make torque, and, depending on the load, how much. The ability of the engine to continue to overcome the applied load as the RPMs climb by making more torque shows it's ability to make HP because time now creeps into the equation. Either by over-coming a steady amount of load at a higher RPM or by over-coming a greater load at a steady RPM.

Maintain the same load and keep increasing the RPM until the load can no longer be over-come OR maintain a steady RPM but keep increasing the load until the engine can non longer over-come.

Another problem I see is that on an engine dyno, there's no gearing involved, just a load applied to the engine which must be overcome. The engine's ability to over-come that load then cmultiplied using the time factor (RPM) will give you the HP.

Didn't we run the gambit on this topic more than a year ago?

Jake

 

Well, no, it doesn't.

Visualize yourself holdinga one pound object in the air. If the object neither drops or rises, your applying 1 lb/ft or torque to just maintain it there, but since it isn't moving no work is being done so you have no (HP).

1 lb/ft of torque applied to a one pound object only maintains equalibrium and no work (HP) is being done. So you have torque, but no HP. Now as soon as you begin to move the object, either up or down, time comes into the equation, so work begins to be done. How fast you move it is an indication of how much torque you're creating and from that you can calculate HP. The more torque you can create the faster you can move the object, the less the slower.

When your torque falls below the amount of one lb/ft, the object begins to drop toward the floor since the torque you are creating can no longer over-come the load. HP then plummets.

Last time I chimmed in on this topic, guys began flexing their physics muscles by talking about polar moments and inertia and all sorts of stuff from their physics classes which had my head spinning. Hope it doesn't happen this time.

Crazy stuff ain't it.

Jake


[Modified by JAKE, 9:16 AM 3/27/2002]