Aces High Bulletin Board
General Forums => The O' Club => Topic started by: Monk on May 09, 2005, 11:40:15 AM
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My wife just picked up a fun little car, a diesel. 130hp and 300 lbs ft or so of torque. I was surprised how fun this car is to drive. Midrange pull is outstanding.
So whats more fun HP or torque, or is it a happy middle.
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it's all about where the torque is. high RPM or lower.
HP gives power, but torque puts you back in your seat
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Torque and HP
What you want is a nice beefy but flat torque curve though its no not much use if that all happens without much HP.
A good example of all power no torque are the wizzy Jap sport bikes. Short stroke motors high HP but bugger all torque so you have to rev the t*ts off them to get em to go.
All Torque not much power is something like a standard twin pot Harley. Plenty of punch but runs out of breath as the revs rises.
( cue Jackal and Laz telling me they rode harley's with 300hp :lol )
A happy medium is a longer stroke big CC multi cylinder motor.
Longer stroke, heavier Flywheel, = Torque
Multi Cylinder = HP
=:D
I know this is bikes but similar to cars just the best examples I know to illustrate the point.
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trim out the torque effects or your foot falls asleep
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i'm bias on the matter.
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Just because you have an HP computer does not mean you have to withhold your opinion Torque.
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Originally posted by Skuzzy
Just because you have an HP computer does not mean you have to withhold your opinion Torque.
BWHAHAHAHHAHAHAHA!!!!!!!!!!!11
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Horsepower = Torque X RPM / 5252
What that means is that horsepower is merely a measurement of how fast you make torque. One cannot exist without the other.
The horsepower and torque curves will always intersect at 525 RPM.
The 5252 constant is why you do not see big HP numbers at low RPM. Unless of course you count big diesels. Most big diesels are rated at less than 3500 RPM. Figure out how much torque a Detroit Diesel 8V92TTA has to make to be rated at 650HP at 3200 RPM. It makes 550HP at 2500 RPM.
A dynamometer measures torque, horsepower is merely a calculated result thereof.
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>Horsepower = Torque X RPM / 5252
agree with you there
>The horsepower and torque curves will
>always intersect at 525 RPM.
disagree with you there. its the product of (torque x rpm) / 5252 so hp and torque curves do not always intersect at a constant rpm range.
I think of peak torque as when the engine rate of power produced is greatest measured in mechanical work or ft lbs. HP is the value of total energy produced negative the power loss through heat/friction.
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Do the math.
Since the constant in the formula is 5252, when RPM also equals 5252, torque and HP are equal, because HP is a calculation of torque times RPM dvided by the constant.
If the RPM is 5252 and the constant is 5252, what happens?
Put another way, if you divide a number by 5252, and then multiply it by 5252, what happens?
500 ftlbs of torque multiplied by 5252RPM equals 2626000.
2626000 divided by 5252(the constant) equals 500 horsepower.
So yes, if calculated correctly, torque and horsepower will always be equal at 5252 RPM because horsepower is a calculated derivative of torque and RPM in a formula with 5252 as a constant divisor of torque multiplied by RPM.
Spend 25 YEARS of your life with engines on a dyno, and you'll be asked about that and explain it often enough that you'll never forget it. If you test in that range, and print the results, 99 out of 100 customers will ask you: "Why is torque always equal to horsepower at that same RPM?" OR they will say: "That's weird, every engine you've ever dynoed for me always has the torque and horsepower equal (or the torque and horsepower lines on the graph always merge) at 5252 RPM."
Now, neither peak torque/RPM nor peak horsepower/RPM can be stated as always being the point of peak efficiency. There are too many other factors involved. There's the point of highest volumetric efficiency, there's the point of best BSFC (brake specific fuel consumption, or the point where the engine consumes the least amount of fuel per unit of power developed) or a couple of others I won't go into here due to time constraints. There's thermal efficency and friction loss as well.
Theoretically, the peak horspower RPM would be where the engine is most efficient, since it is producing the greatest amount of power in the least amount of time.
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Torque
(http://www.turbobuick.com/img/rich_wheelie.jpg)
Horsepower
(http://www.ss427.com/c5-corvette-180-mph.jpg)
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I dont think the constant 5252 is the rpm. I believe its derived from some formula relating to conversion of a force of torque to circular movement.
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an engines torque is mechanical force in circular motion. Hp is a value of energy and can be converted to something like a btu or kilowatt. So the constant 5252 is so that you can convert mechanical force to a value of power. Thats all it is.
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Since the constant in the formula is 5252, when RPM also equals 5252, torque and HP are equal, because HP is a calculation of torque times RPM dvided by the constant.
If the RPM is 5252 and the constant is 5252, what happens?
(torque x rpm) / 5252
I agree, at 1rpm thats true.
gotcha. ;)
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I admit I had to look it up though, here are my sources. :lol
http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm
http://www.revsearch.com/dynamometer/torque_vs_horsepower.html
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Definitions:
P = Power [lb-ft/s]
Tau = Torque [lb-ft]
Omega = Angular Velocity [radians/s]
P [lb-ft/s] = Tau [lb-ft] * Omega [rad/s] (1)
Unit Conversion 1:
550 lb-ft/s = 1 hp
or
P [hp] = (1/550) * P [lb-ft/s] (2)
Unit Conversion 2:
1 RPM = 2*pi/3600 rad/s
or
Omega [rad/s] = 2*pi/3600 Omega [RPM] (3)
So take (1):
P [lb-ft/s] = Tau [lb-ft] * Omega [rad/s]
Substitute (3)
P [lb-ft/s] = Tau [lb-ft] * (2*pi/60) * Omega [RPM]
Then substitute the result into (2)
P [hp] = (1/550) * Tau [lb-ft] * (2*pi/60) * Omega [RPM]
P [hp] = Tau [lb-ft] * Omega [RPM] * (2*pi/60/550)
Which simplifies to...
P [hp] = Tau [lb-ft] * Omega [RPM] / 5252
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As far as the merits of power vs. torque, one thing to remember. You can always multiply torque with gearing. You can't multiply power. The guy with more power can always outrun the guy with more torque, as long as he's got the right gear.
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Originally posted by FUNKED1
As far as the merits of power vs. torque, one thing to remember. You can always multiply torque with gearing. You can't multiply power. The guy with more power can always outrun the guy with more torque, as long as he's got the right gear.
not when you throw nitro into it .. :D
But then thats a totally different animal .
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Power and torque are diffrent things. When you put them on one graph and use the same scale for power and torque then they intersect.
When you use a diffrent scale then they dont. So what i want to say is they may intersect anywhere they want but it is meaningless, since its only a matter of scale.
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Originally posted by Roscoroo
not when you throw nitro into it .. :D
But then thats a totally different animal .
As long as you've got a crankshaft driving a transmission driving wheels, what I said is true.
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I failed Maths O level, so the calculations are very impressive though I have no idea what you are all on about!:lol
Do they mean that I was kind of right or completely wrong!?:confused:
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Funked is teh smart. But he plays too many car racing computer games.:D :aok
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Savage cheats!
He knoes full well a steam locomotive produces maximum torque at zero revs....
:)
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skyprancer... you should stick with bikes.
I think the question is what is more fun. HP will allways make torque.
In my 3700 lb el camino that is a daily driver I have a large engine with a lot of torque (and HP) down low. hyd cam, dual plane manifold, oval ports, vac sec carb etc. I could make more hp and torque at higher RPM but it would kill the low end where the car lives all the time. Lot's of low end grunt get the heavy car rolling and make it more "fun".
My 2100 lb Healey is the oppossite. short stroke 331 with high lift duration solid lifter cam.. single plane victor manifold, big ported heads and big mechanical double pumper with huge amounts of initial advance.
It doesn't need any low end torque to move it out. It reaches 2500 rpm or more a sec after the clutch is out at launch. I need the "time" it takes to get to 6500rpm or so to shift (you are very busy in the car). It is easy to keep the car in the high RPM range where it makes a lot of HP and therefore "fun".
skyprancer brought up Harleys... if they weren't fun... pepole wouldn't ride em.. they are fun because of low end torque. That is where most people use them. The "fun" is 90% of the time.
the jap bikes make theirs at very high RPM's are are "fun" there.. they are light and get there fast but... most people can't use any of the Hp they produce more than about 10% of the time. the rest of the time they are less fun than a torque bike. You have to really be breaking the law big time to enjoy em.
The torque vs hp pictures were missleading to... the "torque" picture showed a buick gn that is a very small turbo v6. not a low end torque motor at all. the speedo was the hp example.. again.. missleading. gearing can take advantage of torque and hp in any car. A big block that only revs 5500 for instance will rev it with 4.11 gears in top or with 2.75's in top gear. A car with no top end torque that revs 8000 will not pull the 2.75's
lazs
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Lazs, once again bests Skyprancer. WTG!
Karaya
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well... I would just as soon not be known as "the guy who could best skyprancer." Sorta like "that comedian that beat up the women in the ring"
Another thing... hp with narrow torque range (small highly tuned motors say) are capable of better acceleration times with the right gearing than similar big cube motors with very broad torque bands but... real life.... no matter what gear the tuner motor manages to shift down into... in a contest on the freeway say... the big motor is gonna walk away. that is a huge factor in "fun". Being pushed back in the seat is worth a lot sensory wise.
BMW bikes are sorta that way (to get away from Harleys which skyprancer knows nothing about) their quarter mile times for the oilhead (and old airhead) bikes were not stellar bu... in roll on throttle tests they allways beat the more hyper bikes that could beat em by allmost a sec in the quarter mile and... with very little apparent effort.. this is a function of a broad torque band.
lazs
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Always thought that a hp was the force that pulls what, 75 kg? up one meter in one second.
Torque i generally know as NM.
I had a car, rated 90 hp, 1600 cubic petrol engine, Torque was rated at some 80 nm.
My tractor had a diesel engine, 3860 cubics, rated 90 hp, torque was 341 Nm.
So, how do you figure that one?
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Originally posted by lazs2
Another thing... hp with narrow torque range (small highly tuned motors say) are capable of better acceleration times with the right gearing than similar big cube motors with very broad torque bands but... real life.... no matter what gear the tuner motor manages to shift down into... in a contest on the freeway say... the big motor is gonna walk away. that is a huge factor in "fun". Being pushed back in the seat is worth a lot sensory wise.
Yup, that's what I'm seeing with this car. the pull on the autobahn in 5th or 6th gear from, say 60mph to 100mph is "fun". The top speed is about 135, but getting up there. Yes, that's fun. Not a big engine or car, but very surprising.