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Old 07-01-2005, 01:11 AM
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???the 411 on HP now & then ???

is it just me or do we as hotrodders from the the days of future passed have /had a different formula for measuring horse power ratings??
or did the automotive industry change it to make these modern disposable cars seem more appealing??

sr66

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Old 07-01-2005, 02:10 AM
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There are least 3 different methods of getting HP.

The current HP ratings are much more accurate and are lower than old style readings.
but... HP is "imaginary", really it's all about Tq and that's why the 215 hp mustang blows the 215 hp honda off the road.
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Old 07-01-2005, 02:21 AM
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i was kinda thinking they would be lower so how dose it work?

sr66
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Old 07-01-2005, 06:51 AM
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Not all HorsePower is alike so here are the following, wich hopefully make your life a bit easier.

KINDS OF HORSE-POWER

Formula: 1.0 SAE HP = 1.01411685309470545 DIN & PS HP = 0.7457121551081283 kW

Explonation:

1.[ BHP ] or Brake HorsePower ca refer to both SAE and DIN (mesured at the flywheel on an engine dyno)

2.[ NET HP ] This standard was used during the musclecar era & it mesured a Max total output of an engine. However it was not as reliable as SAE because the more options (ex: power brakes, power steering, A/C, ect.) you added the more power was lost to accelerate the car.

3.[ SAE HP] used in United States and Generally in North America. (it mesures an engines max power output with everything turned on ie: A/C, heater, radio, lights ect.)

4.[ DIN HP ] (a standard of mesurment used in Europe, generraly between 3-8hp [5 on avg.] is lost in the conversion from DIN to SAE, this is due to emmision and noise standards)

5.[ PS or JIS ] a standard equal to DIN metric mesure of power, used in Germany & is set according to the air pressure generated in the combustion chamber of a cylinder (mostly used in Germany & Japan/Asia though some Euro countries also use this scale)

6.[ kW ] The Kilo WAT is a standard of mesure used genneraly in Electric Motors & generators which can also be applied to combustion as well as well as propulsion motors. (this standard is widely spread accross the world, it is however used in Europe a lot more than in North America.

7.[ RWHP ] or Rear Wheel Horse-Power is the most difficult to estimate but the easiest to mesure. Genneraly new & newer cars are more efficient therfore thay only loose between 11-25% of power as it travels to the ground. Older and Old/Classic cars were considerably more inneficient and could loose 30-50+% of power in this process. When analizing this, we also have to take into account that Automatic transmission by in large are less efficient than Manual transmissions, while Electro-hydraulically actuated (ie: Ferrari 360 modena) gear boxes are somwhere in the middle.
(mesured on a drive on Dyno and it mesures power that is transfered through the tires to the ground, and it takes into account transmission, gearing and differential efficiency. It is considered the most acurate form of testing HP in cars and motorcycles, as each manufacturers efficiencies vary wildly across the globe, therefore the only thing that counts is real world power)



KINDS OF TORQUE POWER



Formula: 10 ft-lbs = 13.8273 Nm = 1.4105215052172965 kg*m

A.[ THRUST ] in Pounds or Kilograms, this standard is used in Aero & Space-industry and it messures the air pressure output of a JET or Rocket engine. 19000 pounds of thrust translates roughly into 36000 HP.

B.[ LB-FT or ft-lbs ] (foot-pound) or engines abillity to lift (up) an amount of pounds in a distance of 1 foot in one second. Generally used in North America.

C.[ Nm (Newton Meter) ] a scale named after a famous scientist (Sir Isaak Newton) that is very much like lb-ft the only diferance beeing is that it uses the Metric system when mesuring the output. Again it mesures an amount of lifting power in Joules at a distance of 1 meter in one second. Used in Europe & abroad.

D.[ KG*M ]killograms lifted in a distance of 1 meter of the ground.
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Old 07-01-2005, 07:32 AM
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Quote:
Originally Posted by NDNslicks4me
There are least 3 different methods of getting HP.

The current HP ratings are much more accurate and are lower than old style readings.
but... HP is "imaginary", really it's all about Tq and that's why the 215 hp mustang blows the 215 hp honda off the road.
I don't know if I'd agree with that fully. I see where you are coming from, but honestly, if you're going to measure something like a race, you're measuring force over distance, and that's work, and the rate of that work is power, which can be measured in watts or joules, but in this case, horsepower.

Horsepower can be derived from a torque rating, just as torque can be derived from HP: (Torque= Horsepower*5252/RPM). My point in saying this is that they're just two ways of measuring two physical phenomena. They're not even the same unit! A torque rating will tell you the amount of work that can be done. If you somehow hooked up a torque wrench to the center of a wheel of a bigrig, how hard would you have to push to get that wheel to move? 100lbft? 200? 400? That number is the minimum number of torque required to do work. Horsepower, on the other hand, will measure how fast you can apply that work. How fast can we move the bigrig from one end of a 1/4 mile track to the other? Better look to a hp rating for that one.

Your example about the 215 HP honda and mustang I think would probably be a close match due to the honda's light weight. I'm pretty confident, however, that the real reason the mustang would pull ahead has less to do with its brute torque number and more to do with its available power at any given point in its curve. The mustang has probably a nice, flat power curve/torque curve, whereas the honda is a rather "peaky" motor. Goes back to the old saying "peak numbers mean nothing!" I tend to agree with that.

Anyway, I'm not sure how much of the above you already knew, just making my stance clear on the issue and for the newbs who read up on this sort of stuff.

K
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Old 07-01-2005, 12:44 PM
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it was torque that ruled the roads when muscle cars roamed the earth! todays cars arent makin 550ft lbs stock along with that 350hp. muscle cars pull , oh man do they pull

hondas have a serious disadvantage with only 130 ft/lbs. killers right. they lighten it 1000lbs an stuff a 5spd with close ratios. then add retarded gearing to multiply it back. after all torque can be multiplied through gearing. not hp.

you want a fat powerband where you use it.

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Old 07-02-2005, 05:56 AM
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Quote:
Originally Posted by killerformula

Your example about the 215 HP honda and mustang I think would probably be a close match due to the honda's light weight.
So the 215 HP is NOT EQUAL if the weight must be lighter to compensate?
Quote:
Originally Posted by killerformula

I'm pretty confident, however, that the real reason the mustang would pull ahead has less to do with its brute torque number and more to do with its available power at any given point in its curve. [
It's "avaliable POWER at any given point" would be TQ and you know it.
Quote:
hondas have a serious disadvantage with only 130 ft/lbs. killers right.
Killers right or i'm right? killer says HP says how fast you accel and I say it's Tq. so if the Hp is the same and Tq is different , and I'm saying it is Tq makes the difference who's right?

Ok, now take that same 215 HP honda and drop it in the stang. hardy har har. oh, not fair? ok then drop the gear so as to pick up the Tq you lost. WHAT, it still won't hang? well what's going on guys? you have the same Hp and have geared it so the Tq to the rear wheels is the same but it's still losing, WHY?

maybe I'm just being facetious.
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Old 07-02-2005, 08:46 AM
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Quote:
Originally Posted by NXS
So the 215 HP is NOT EQUAL if the weight must be lighter to compensate?
215 horse is 215 horse no matter how you slice it. The honda would have to be a bit lighter because during 90% of the curves of these two motors, the v8 is making more power.

Say the mustang makes 215 horse a 4800RPM, and the honda makes 215 horse a 8500RPM. If you had 100% traction and you hooked up the honda and the mustang with zero wheel spin, and you ran the honda's motor at 8500RPM 100% of the time from one end of the track to the other, and did the same for the mustang at 4800RPM, you'd have one losing mustang due to its weight. Hope you're not racing for pinks!


Quote:
Originally Posted by NXS
It's "avaliable POWER at any given point" would be TQ and you know it.
Absolutely not. I dont even have to argue that one, you're just flat out wrong in your terminology there, here, I'll show you: Torque is a measurement of LB/FT. That's number of lbs of directional force around an axis over the distance of one foot. This unit is called a unit of work. Horsepower, on the other hand, is a unit of power or work over time. This is a rate of doing work.

Quote:
Originally Posted by NXS
Killers right or i'm right? killer says HP says how fast you accel and I say it's Tq. so if the Hp is the same and Tq is different , and I'm saying it is Tq makes the difference who's right?
Ok, fair enough, here's the challenge: if torque is the measure of acceleration, then your next post will include a detailed physical analysis of a car (I'll let you chose whatever you want) accelerating from one end of quarter mile to the other using only its torque figure, and I'll do the same, only I'll just use an average HP number. Sounds fair to me!

Quote:
Originally Posted by NXS
Ok, now take that same 215 HP honda and drop it in the stang. hardy har har. oh, not fair? ok then drop the gear so as to pick up the Tq you lost. WHAT, it still won't hang? well what's going on guys? you have the same Hp and have geared it so the Tq to the rear wheels is the same but it's still losing, WHY?
As long as with gearing you can AVERAGE the same amount of power (and we discussed what that is already) at any given time during acceleration, you'd have a pretty close race. Closer than I think you'd imagine.
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Old 07-02-2005, 08:55 AM
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i think thaty in reality this race is won at the starting line.

more edits to come.
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Old 07-02-2005, 09:00 AM
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Quote:
Originally Posted by spinn
i think thaty in reality this race is won at the starting line.

more edits to come.
Truest thing said yet!

I would further qualify the above with saying that I'm not saying a vehicles torque rating is a meaningless figure, or that in certain circumstances it doesn't hold a high importance (starting line, for instance). But in answer to the above, if you're going to measure how fast one object gets from one place to the other, that's simply a measurement of power. Further, if you want to measure how fast something accelerates, that's also a measurement that involves a power rating.

K
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Old 07-02-2005, 09:04 AM
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somewhere i read a windmill has like 20,000 ft/lbs of torque, but only like 5 hp. so i think killers right. it takes more than torque.

what can you do with the torque? how it can be used, you know?

i dont know if the figures are right, it is my feeling that the package win the race. nxs makes good points, but im looking at a bigger picture
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Old 07-02-2005, 11:24 AM
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All i'm saying is HP is a mathmatical number, derived from Tq & RPM.

The problem is that as people try to build HP they give up the Tq and lose out in the end. {the best way is to focus on max Tq at the highest RPM possible}

The windmill with 20,000 Ft/lbs & 5 Hp would only be turning at 1.5 rpm, not really a fair compraison.

The thing is where you've gotta keep the engine at a certain RPM constant to make the honda hang with the 5.0 is that you're going to lose out thru mechanical inefficiency in the long run. Not only thru drag/friction of componets but also thru weigt of the componets.

That 215 honda Hp is peak as is the stang and it, at the specific rpm, is equal {if gearing is taken into account, and ONLY IF}. The simple fact is that HP figures are misleading when trying to truely understand power.

That 215 honda @ 150 ft/lbs is NOT equal to 215 @ 300 ft/lbs. {actually it is on paper but when the power is being applied it's not}.

300 ft/lbs @ 3750 =215 hp
150 ft/lbs @ 7500 =215 hp

lets add some 2.00 ratio gears to that equation and put them on the Honda and we end up with the EXACT same numbers as the 5.0. {300 ft/lbs @ 3750 =215 hp} we had to add weight and friction which the little formula doesn't take into account.

But still yet we now have a honda that will {using the extra gear} make identicle power{in a perfect world with no friction losses}. it is going to still redline at 7500 {now 3750 with the extra 2.0 ratio gear reduction/Tq multiplication} while our 5.0 can rev to 5500 allowing for some extra gear. the 5.0 still wins.
If you could take a 215 Honda and Beat a 5.0 with the same weight people would but we know in real life it just doesn't happen like that.
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Old 07-02-2005, 12:05 PM
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Quote:
Originally Posted by NXS
lets add some 2.00 ratio gears to that equation and put them on the Honda and we end up with the EXACT same numbers as the 5.0. {300 ft/lbs @ 3750 =215 hp} we had to add weight and friction which the little formula doesn't take into account.

But still yet we now have a honda that will {using the extra gear} make identicle power{in a perfect world with no friction losses}. it is going to still redline at 7500 {now 3750 with the extra 2.0 ratio gear reduction/Tq multiplication} while our 5.0 can rev to 5500 allowing for some extra gear. the 5.0 still wins.
215Hp is 215hp. If its measured at the crank it includes all the frictional losses from the engine. If you want to argue that its a less efficient 215 horse on the honda than the stang, be my guest, I won't argue with you one way or another. That topic really doesn't interest me.


Quote:
Originally Posted by NXS
If you could take a 215 Honda and Beat a 5.0 with the same weight people would but we know in real life it just doesn't happen like that.
Well, in your first post you weren't talking about equal weights, but that's really beside the point. The only reason the stang will win is because its making more horsepower for a longer amount of time than the honda. Forget about peak numbers for a minute. These two cars come off the line and the mustang, because of its much larger engine, is immediately making more power. Heck, the honda is probably even geared a little shorter than the stang! So after 2 seconds of race the stang is at 3800RPM making about 175 horse, and the honda is at about 5000 RPM making 110HP. 4 seconds after the start the stang is just passing his power peak at 4800RPM, and is running about 5200 and is just stepping on the clutch. He's making about 200 horse right now, and has just passed his peak number of 215 horse. The honda is still singing its way up to its power peak, and is running 7800RPM @ 185 horse. Man, things aren't looking good for the honda, are they? He's even climbing RPM faster than the stang but just can't keep up! Well its going to get worse when they shift into second. Mr. Stang dumps the clutch and starts reving through second gear, starting at about 3300RPM where he makes around 150 horse, after say about 6 seconds of race. Right about now the honda has just passed his power peak and is getting ready for second, which sits him back to about 5000 or 5500 RPM, and he's only making 115 or 125 horse at this point and has a long way to go for 8500 RPM. He's probably already seeing the doorlines of the stang and will soon be seeing brakelights...

Why? because he peaks at the same horsepower number, yes, but his curve in the honda is much less forgiving than in the v8 stang. Even with a lighter car and more gear, he's going to have real problems keeping up.

Quote:
Originally Posted by NXS
All i'm saying is HP is a mathmatical number, derived from Tq & RPM.
I don't understand why you think this. Horsepower (well, any unit of "power" anyway) is the only quantitative measurement of how you can get a certain mass from one point to another in a given amount of time. Its just as simple as that, that is the point of the unit of measurement. You just can't do that with a torque number. I'm not saying one's better than the other or one is more useful than the other. I"m saying if you want to measure what a car did in a race, horsepower is the measurement you need. If you want to measure how much force it takes to move a given object, regardless of the amount of time it takes, torque is a useful measurement of work, and you can use that. Two units, two uses. In this case, its plain to see that a power unit is the proper one to use, unarguably.

K
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Old 07-02-2005, 12:25 PM
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Horsepower cannot be physically measured, it can be mathmatically figured.
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Old 07-02-2005, 12:30 PM
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Quote:
Originally Posted by NXS
Horsepower cannot be physically measured, it can be mathmatically figured.

OK, you can't see air either, but it doesn't make it any less real. There are many units that cannot be directly measured, but I don't think that means that they're any less important. Directly quantifiable or not, horsepower is the unit of measurement for this operation.

K
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