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06/01/2005 09:13:49 PM · #1 |
I was working on comparing vehicles, and got to thinking that I should do a write-up on horsepower. Of course, I thought I'd post it here too just incase anyone's interested. Any comments, please add them, or if you have questions, ask.
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What is horsepower and how important is it?
I feel that today, auto makers are a bit deceptive in their marketing when they talk about their 'most horsepower in its class' and so on. So I'm writing this so you can see for yourself what the difference between horsepower and torque is, which one is more important, and to explain why it's more important.
Horsepower is defined as the work done over time. It's overrated and it really doesn't tell you much at all about an engine, if anything at all. It's hardly useful when comparing one engine to another. So am I saying that 300 horsepower doesn't necessarily equal 300 horsepower? That's correct. Don't buy it? I'll prove it.
OK...well, for the most part, 300 horsepower is definately 300 horsepower, I'm not going to lie to you. That doesn't necessarily mean that just because two vehicles put out 300 horsepower, that the playing field is even. Let's take out everything else involved in a race, that would be everything including weight, the power curve, traction, and anything else that effects the speed of a vehicle.
Horsepower is equal to torque times RPM divided by 5,252 (HP=Torque * RPM / 5252). Sounds goofy, right? Well, it's a nice easy way to make your car or truck sound faster and more powerful than it really is. Let's take compare two trucks...A 3500 I-5 from a Chevy Colorado and a 4.0L v6 from a Ford Ranger.
Colorado: 220 max HP @ 5600 RPM
Ranger: 207 max HP @ 5250 RPM
The Colorado seems more powerful, right? Well, it must be because it has more horsepower. That's not so. When you convert the HP figures into what each engine is putting out in torque at the given RPM's, we see that the Colorado is putting out 207 LB-FT and the Ranger is putting out 207 LB-FT of torque. The Colorado's power band is higher...so it LOOKS more powerful.
Horsepower cannot be felt. Torque can be felt. Torque is what throws you back into your seat in that race car. It's what gets a vehicle off the starting line and what pushes it through the finish.
Let's compare two hypothetical vehicles so I can further illustrate my point. Let's call the two engines Engine A and Engine B. Here are the stats...both are MAX horsepower.
Engine A: 200 max HP @ 5900 RPM
Engine B: 100 max HP @ 2000 RPM
Engine A is putting out DOUBLE the horsepower. That's pretty impressive. But when you look at it closer, Engine A is putting out 178 LB-FT and Engine B is putting out 263 LB-FT or torque. Remember, torque is the one that you can feel, and is the one that determines how fast it can push your vehicle and how fast it can get you to that speed.
Another thing I thought was of worthy mention is that just because a certain modification may increase your horsepower by 5 points, you're not necessarily gaining power. You could simply be shifting your max horsepower point and actually losing power in the long-run.
Of course, there are other factors that affect how quick your vehicle is going to cross the finish line such as weight, traction, and the power curve. For the most part, however, remember that just because one vehicle has 250 horsepower and another has 200 that doesn't mean that the first vehicle is faster or even more powerful for that matter. Text Copyright © 2005 David Paull
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06/01/2005 09:22:47 PM · #2 |
Which car is lighter? Power to weight ratio?
Message edited by author 2005-06-01 21:39:41.
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06/01/2005 09:26:27 PM · #3 |
Which one has pretty flowers on it? hmmmm?
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06/01/2005 09:27:03 PM · #4 |
| Horsepower is a measuring systym used to measure the power of a vehicle or power tool. For example...a Chevrolet Corvette has 400 horsepower at a specific RPM. So when you reach a certain Rotations Per Minute, the maximum horsepower can't exceed 400. Torque is pulling power. Trucks have more pulling power. Torque is measured by Pounds per Foot. Usually a large cubic inch engine has more Torque. Example...a Dodge Viper has the same amount of horsepower as a Porsche Carrera Turbo. The Viper has more Torque, which means that if the 2 cars were to race uphill, the Viper would beat it. I don't know if 400 horsepower actually is equivalent to the power of 400 horses as in the animal. I don;t know how accurate that is. |
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06/01/2005 09:31:55 PM · #5 |
Dave,
Who cares... by 50,000 miles each of them will have been in the shop a half dozen times for repairs and probably been recalled once or twice. The owners by then will be on a first name basis with the service manager at the dealer
Buy the Tacoma, just turn the key and drive with no repairs, or recalls, and don't worry about the "closed course, professional driver, do not attempt" hype commercials |
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06/01/2005 09:36:46 PM · #6 |
Deapee is correct that there is quite adifference between power, and useable power. It's an old axiom that "people buy power, but drive torque." What's meant by that is that people often are convinced to purchase a vehicle based on a high horespower number, but enjoy driving vehicles that have lots of torque, though not necessarily high power.
It's why my little Jetta diesel, with 90hp and 155 lb-ft of torque is actually reasonably fun to drive. It's not fast, but it's not the dog the horsepower number would have you believe, and will leave a nice patch of rubber off the line.
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06/01/2005 09:37:07 PM · #7 |
Ok. So, what's with the 5,252 number, and what's BHP?
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06/01/2005 09:38:56 PM · #8 |
Did you see the news tonite?
2 things... Toyota has an issue with it's Prius. Seems to shut off at random at 35-60 mph while driving. No idea as to what is causing it...
GM is selling EVERY vehicle at the employee price (so says the news...try certain Vette's and i bet the answer is NO). That can save you upwards of 8 grand.
OK, my brother in law works for GM. I can buy a ford for less money than a GM with his discount (same sticker price before negotiations)
$1600 of every GM car sold goes to paying for the retirement of GM workers.
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06/01/2005 09:41:52 PM · #9 |
Originally posted by BikeRacer:
Ok. So, what's with the 5,252 number, and what's BHP? |
BHP Brake Horse Power. Before 1972 HP was measured at the engine, with no accessories running. Starting in 72, the measurement included accessores (water pump, alternator, maybe more). BHP is measureed at the rear wheel I beleive and includes the losses of HP in the transmission and differential. it takes HP to turn all those parts... You can lose 20% of the HP in the transmission alone.
The 5252, or whatever the specific number is, is the crossover in the HP/Torque graphs. Torque is what is measured and a mathematical formula is used to derive the HP number.
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06/01/2005 09:43:04 PM · #10 |
Originally posted by BikeRacer:
Ok. So, what's with the 5,252 number, and what's BHP? |
I believe BHP is braking horsepower...the measure of force used to stop an object in motion? I could be wrong.
5,252 is just a made up number that is used to get horsepower...which helps to prove my point that horsepower is a useless figure at best.
But you brought up another interesting point I forgot to mention...in all torque and HP charts, at 5,252 RPM, they will always be equal (now that you know the formula, that is quite obvious).
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06/01/2005 09:44:43 PM · #11 |
Originally posted by BikeRacer:
Ok. So, what's with the 5,252 number, and what's BHP? |
the 5252 number is just a combined conversion factor for units of measure. BHP stands for Brake HorsePower, and is the useful power delivered, usually measured on a dynamometer. It takes into account drivetrain losses (each time you transfer power through a gearset, you lose anywhere from 2-5%).
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06/01/2005 09:48:06 PM · #12 |
Originally posted by Prof_Fate:
$1600 of every GM car sold goes to paying for the retirement of GM workers. |
Besides lack of quality, that's another downside to allowing your company to become or continue to be unionized |
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06/01/2005 09:51:34 PM · #13 |
| thanks for the info! but, will any of this make my camry outperform my girlfriend's audi? =[ |
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06/01/2005 09:53:23 PM · #14 |
Originally posted by BikeRacer:
thanks for the info! but, will any of this make my camry outperform my girlfriend's audi? =[ |
Sure, if you swap the motors 'round ;-)
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06/01/2005 09:54:37 PM · #15 |
Originally posted by BikeRacer:
thanks for the info! but, will any of this make my camry outperform my girlfriend's audi? =[ |
Sure, think how much further the Camry will go on the days that the Audi is in the shop |
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06/01/2005 10:05:42 PM · #16 |
Originally posted by photodude:
Besides lack of quality, that's another downside to allowing your company to become or continue to be unionized |
So I guess you think workers that don't have pensions build better cars?
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06/01/2005 10:10:01 PM · #17 |
Originally posted by coolhar:
Originally posted by photodude:
Besides lack of quality, that's another downside to allowing your company to become or continue to be unionized |
So I guess you think workers that don't have pensions build better cars? |
Actually the Toyota workers do have a retirement plan... it's a 401k, which is what most of us have. GM and Ford are locked into archaic Defined Benefit plans (which are these days usually provided only to unionized workers and gov't workers) Unfortunately for these workers, the pensions and retirement plans are going to be big contributors to the bankruptcy of both of those companies |
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06/01/2005 10:19:05 PM · #18 |
Originally posted by photodude:
Unfortunately for these workers, the pensions and retirement plans are going to be big contributors to the bankruptcy of both of those companies |
Wrong. Companies go into bankruptcy when they are mismanaged, or when they are looted. Blameing unions is just a currently popular scapegoat to mollify stockholders and politicians.
And what does that have to do with photography? or horsepower? That kind of stuff belongs in the rant forums.
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06/01/2005 10:42:56 PM · #19 |
Originally posted by BikeRacer:
thanks for the info! but, will any of this make my camry outperform my girlfriend's audi? =[ |
yep get a 100 shot of NOS :)
James |
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06/01/2005 10:45:43 PM · #20 |
Explanation of 5252
First, 1 horsepower is defined as 550 foot-pounds per second. The units of torque are pound-feet. So to get from torque to horsepower, you need the "per second" term. You get that by multiplying the torque by the engine speed.
But engine speed is normally referred to in revolutions per minute (RPM). Since we want a "per second," we need to convert RPMs to "something per second." The seconds are easy -- we just divide by 60 to get from minutes to seconds. Now what we need is a dimensionless unit for revolutions: a radian. A radian is actually a ratio of the length of an arc divided by the length of a radius, so the units of length cancel out and you're left with a dimensionless measure.
You can think of a revolution as a measurement of an angle. One revolution is 360 degrees of a circle. Since the circumference of a circle is (2 x pi x radius), there are 2-pi radians in a revolution. To convert revolutions per minute to radians per second, you multiply RPM by (2-pi/60), which equals 0.10472 radians per second. This gives us the "per second" we need to calculate horsepower.
Let's put this all together. We need to get to horsepower, which is 550 foot-pounds per second, using torque (pound-feet) and engine speed (RPM). If we divide the 550 foot-pounds by the 0.10472 radians per second (engine speed), we get 550/0.10472, which equals 5,252.
So if you multiply torque (in pound-feet) by engine speed (in RPM) and divide the product by 5,252, RPM is converted to "radians per second" and you can get from torque to horsepower -- from "pound-feet" to "foot-pounds per second."
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06/01/2005 10:49:40 PM · #21 |
good topic, I havent talked cars since I sold my BMW 3 years ago. Before that my daily driver, a 99 trans am, was doing 12.6 in the 1/4 mile. several dyno test showed 324 RWHP (rear wheel horse power) and 342 ftlb of torque.
Well it was doing better than that but I sold it before I got a chance to take it down the track with a few more tweeks and mods, but a few street races proved it was close to 12 seconds in the 1/4 as I kept up with a buddy of mine who was in the 11's
The horse power is what allows you to obtain high speeds, torque gets you to the high speed fast.
James |
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06/01/2005 11:04:06 PM · #22 |
You have Torque + HP ,but the vehicle weight and how the power is applied to the wheels is also very important!
I used to drag race with my '98 GTI VR6 and I saw a lot of Mustangs with lot of horses in the dust :-) |
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06/01/2005 11:05:26 PM · #23 |
Originally posted by jab119:
The horse power is what allows you to obtain high speeds, torque gets you to the high speed fast.
James |
Thank you for explaining it in English for me...I think I understand now!!! :o)
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06/01/2005 11:20:39 PM · #24 |
Originally posted by laurielblack:
Originally posted by jab119:
The horse power is what allows you to obtain high speeds, torque gets you to the high speed fast.
James |
Thank you for explaining it in English for me...I think I understand now!!! :o) |
I'm glad I'm not the only one that was lost.
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06/01/2005 11:22:58 PM · #25 |
| When you say it's torque that make the car accelerate, you really mean torque at the wheels, not at the engine. You can trade off torque for rpm with different gear ratios. So, horsepower (relative to weight) is what really matters in determining how quickly you can accelerate. Given equal weight, the car with more peak horsepower can go faster - if the gear ratio is chosen correctly it can get more torque to the wheels. |
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