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Discussion Starter #1
i was looking at what some of the forum members are dyno'n and it made me wonder where on Earth they got the 140 hp rating for my 2002. I only bring this up b/c i recently read an article about the lost ponies in 2000-2002 (i can't remember) Cobra. The factory claimed one thing and people started to dyno their cars and saw that it was under what the factory stated. They got recalled and the owners were pissed! Is it a standard in the indusrty to lie about the horsepower? Can we do anything about it?
Thinkin
Brian
 

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well, what the manufacturer lists as peak horsepower is measured as Brake HorsePower, or Bhp...what dynos record is USABLE horsepower, Wheel HorsePower, or Whp.

Also, the mustang cobra debacle was due to mass airflow sensor size, IIRC...it was too restrictive, so FoMoCo redesigned it and gave free replacements to LOTS of angry Cobra owners. This wasnt a lie on Ford's part, rather an engineering mishap, and an example of bad design stemming from less development (a domestic car company staple).
 

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Many manufacturers also simply overstate just to sell more cars. A good example is *unfortunately* Nissan; they claimed the SE-R was around 170hp or so, and when SCC dynoed it, it was only around 150hp. It's highly unlikely that there is THAT much power loss between the flywheel to the wheels.
 

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FF Drifter said:
Many manufacturers also simply overstate just to sell more cars. A good example is *unfortunately* Nissan; they claimed the SE-R was around 170hp or so, and when SCC dynoed it, it was only around 150hp.
PROVE it.
 

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That's what I was reading in some older issues of Sport Compact Car. Ask them to prove it. I'm just the messenger.
 

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FF Drifter said:
That's what I was reading in some older issues of Sport Compact Car. Ask them to prove it. I'm just the messenger.
But you repeated it as fact. :)

They didn't prove it either.

Now, the Cobra owners did. They pulled at least one engine from a car and put it on a brake dyno and proved it.

I'm not trying to give you undo grief. Just be carefull what you repeat or at least how you repeat it. :)
 

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Fight Fight!:dead:
 

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There's been a certain amount of discussion, in this and other threads, about the concepts of horsepower and torque, how they relate to each other, and how they apply in terms of automobile performance. I have observed that, although nearly everyone participating has a passion for automobiles, there is a huge variance in knowledge. It's clear that a bunch of folks have strong opinions (about this topic, and other things), but that has generally led to more heat than light, if you get my drift :).

You've often heard numerous terms with "horsepower" , "brake horsepower", "wheel horsepower", “indicated horsepower”, "torque" and/or “power”, etc., etc…but don’t know what it really means or how it is inter-related to one another. Well, each and every one of these terms has different meanings. Depending on the context of use, one term might be beneficial over the other, in the marketing perspectives.

In an effort to clarify some of these confusions, I did a few (okay, lots of) researches and applied my engineering knowledge to come up with the following explanation. I hope it is not too technical.

BACKGROUND

The term horsepower was coined by an engineer named James Watt. Watt was using horses to lift coal from coal mines and wanted a way to measure the power available from different horses. He found that, on average, a mine horse could perform 22,000 foot-pounds of work in a minute. He then increased the number by 50 percent and came up with a measurement of 33,000 foot-pounds of work in one minute. This measurement eventually became known as horsepower.

Gasoline engines are known as internal combustion engines and are divided into two general classes, namely two-cycle and four-cycle engines (Otto cycle). A cycle represents one stroke of the piston or one-half revolution of the crank-shaft, a complete revolution therefore represents two cycles. In a two-cycle engine the power impulse occurs at each revolution, while in a four-cycle engine it occurs at every other revolution, hence the terms two and four-cycle engines.

HORSEPOWER EQUATIONS AND HOW IT IS CALCULATED

It is all best explained by following the energy path from the combustion chamber to the wheels. The combustion chamber creates a force on the piston over a distance in a certain amount of time.

(Force)(Distance)/Time = Power

Horsepower = 550(ft)(lb)/s

The crankshaft converts the linear form of power to a rotational form of power.

(Torque)(RPM)=Power

Horsepower = (Torque)(RPM)/5252

The wheels/real axle converts the rotational form of power back to a linear form of power by moving the car forward. When the car accelerates through the quarter mile in a given amount of time you have a measure on horsepower.

DIFFERENCES IN TERMINOLOGIES

Indicated Horsepower (I.H.P): The I.H.P. is the theoretical H.P. which is found by figuring certain formulas, in which the diameter of the bore, the length of stroke in inches, and the number of revolutions per minute form the basis for the calculation. The formulas for this calculation can be found in basic Thermodynamics textbooks. The results found by the use of these formulas indicate, as the term implies, the number of H.P., which that the engine is supposed to be able to develop.

To calculate I.H.P multiply the area of the cylinder by the length of stroke in inches and that product by the number of revolutions per minute then divide by the constant 10000 for two-cycle or 13400 for four-cycle engine.

For example, Four-cycle engine, 4" bore, 4" stroke, 1000 revolutions per minute, constant 13400. Then: 4" bore equals 12.56 area, then 12.56 x 4 equals 50.24 x 1000 equals 50240 divided by 13400 equals 3¾ I.H.P. for one cylinder, then to find the combined H.P. for multi- cylinder engine, multiply by the number of cylinders.

Today, the term “indicated horsepower” is slowly replaced by the term “horsepower or flywheel horsepower”. When the term “horsepower” is used, it is usually implied "flywheel horsepower". This is the horsepower that is usually used by the manufacturers in the new technological era to market their product because it is usually 15% to 20% more than the actual horsepower seen at the wheels, known as “net horsepower” or “wheel horsepower”.

Brake Horsepower (Bhp): Up until 1971, engines were listed with what is called brake horsepower (Bhp). Brake horsepower is a calculation where the engine horsepower is measured at the point of output with no load from a chassis or any accessories and with fuel and ignition operations under ideal conditions. Brake horsepower is often called gross horsepower today. This figure was often used for advertising purposes up to 1971.

An accessory is anything attached to the engine, by any means, which is not required for basic engine operation. By this definition, this would include a power steering pump, smog pump, air conditioning compressor and an alternator. Ideal conditions, often called laboratory conditions, are standardized settings for use during horsepower measurement. During the 1960s they consisted of a barometric pressure of 29.92 Hg and a temperature of 60 degrees F.

Net Horsepower (Nhp or Rhp): Net horsepower, also called road horsepower, (Rhp) is a calculation where horsepower is measured after the load from a chassis and accessories. Essentially, this is the power available at the drive wheel or wheels of a vehicle. This type of horsepower is also called SAE net horsepower. (The SAE or Society of Automotive Engineers is a group responsible for setting various standards within the automobile manufacturing industry.)

In different literatures, net or road horsepower is also known as, or is similar to, “brake test horsepower” or “wheel horsepower”. The B.T.H.P. is the power the engine actually develops in service, and is considerable less than the I.H.P. This depends entirely upon the degree of mechanical perfection attained in the construction of same. If the construction and compression are good, the engine may reach an efficiency of from 80 to 88 per cent. of the I.H.P.

DYNAMOMETER (DYNO) TEST

Owing to the great number of factors which influence the power delivered by high-speed internal combustion engines, the only reliable way to definitely determine the H.P. they actually furnish is by the brake test. The result of this test will be known as wheel horsepower.

Brake Test Horsepower or Wheel Horsepower can be obtained by hooking an engine up to a dynamometer. A dynamometer places a load on the engine and measures the amount of power that the engine can produce against the load.

You can get an idea of how a dynamometer works in the following way: Imagine that you turn on a car engine, put it in neutral and floor it. The engine would run so fast it would explode. That's no good, so on a dynamometer you apply a load to the floored engine and measure the load the engine can handle at different engine speeds. You might hook an engine to a dynamometer, floor it and use the dynamometer to apply enough of a load to the engine to keep it at, say, 7,000 rpm. You record how much load the engine can handle. Then you apply additional load to knock the engine speed down to 6,500 rpm and record the load there. Then you apply additional load to get it down to 6,000 rpm, and so on. You can do the same thing starting down at 500 or 1,000 rpm and working your way up. What dynamometers actually measure is torque (in pound-feet), and to convert torque to horsepower you simply multiply torque by rpm/5,252, as seen by the above equation.

HORSEPOWER VERSUS RPM GRAPH

If you plot the horsepower versus the rpm values for the engine, what you end up with is a horsepower curve for the engine. A graph of this type would points out that an engine would have a peak horsepower -- an rpm value at which the power available from the engine is at its maximum. An engine also has a peak torque at a specific rpm. You will often see this expressed in a brochure or a review in a magazine as "XXX HP @ YYYY rpm, XXX lb-ft torque @ YYYY rpm". When people say an engine has "lots of low-end torque," what they mean is that the peak torque occurs at a fairly low rpm value, like 2,000 or 3,000 rpm.

Another thing you can see from a car's horsepower curve is the place where the engine has maximum power. When you are trying to accelerate quickly, you want to try to keep the engine close to its maximum horsepower point on the curve. That is why you often downshift to accelerate -- by downshifting, you increase engine rpm, which typically moves you closer to the peak horsepower point on the curve. If you want to "launch" your car from a traffic light, you would typically rev the engine to get the engine right at its peak horsepower rpm and then release the clutch to dump maximum power to the tires.

WHY MANUFACTUERE'S CLAIMED HP DOES NOT EQUATE TO NET OR WHP?

The engine's horsepower is used up in four ways. By accelerating the car over a distance in a given amount of time. Aerodynamic drag on the vehicle. Rolling friction loss. Some of the energy is dissipated as heat in the gears, torque converter, wheel bearing, and tires. Inertial losses. It takes energy to speed up a mass. Internal components in the vehicle drivetrain that undergo acceleration draw energy. These components include the pistons/connecting rods changing direction, pulleys, flywheel, transmission shafts, drive shaft, axles, and wheels. The mass of the pistons/connecting rods and valves/springs are always a draw on horsepower. The mass of the rotating components only draw horsepower when the engine increases RPM. Lightening up all of these components will reduce inertial losses. On the plus side, these inertial components, once up to speed, will make your car coast further and can help mileage on the highway. But they kill acceleration so buy aluminum or magnesium rims. The rest of the fuels energy is lost due to the thermodynamic inefficiency of the Otto cycle process (four cycle gas engine). Usually about 60% of the fuels energy is converted to work. The remaining 40% is dissipated as heat. A higher compression ratio will capture more of the fuel energy and make the engine more efficient.

The last two losses, rolling friction and drivetrain inertial losses, can be approximated with a straight percentage loss from the fly wheel back, 15% for manual transmissions, 20% for automatic transmissions.

REMARKS

The information has been put together by numerous literature and it should provides some clarification with respect to the use of terminology when talking about automobile performances.

Cheers.
jIm
 

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I'll have to confirm a few things here, but I'm 98% sure:

1) Brake horsepower is not the same as SAE Gross

2) SAE Net is definitely not the same thing as wheel horsepower

3) Brake horsepower is measured at the crankshaft and can be either SAE Gross or SAE Net. The difference is that SAE Gross is without driving the accessories (i.e. alternator etc) and intake and exhaust is whatever you want it to be. SAE Net is as delievered from the factory with all accesories driven.

4) Dynos

a. A brake dyno holds the engine to a constant speed using a varying load as necessary to maintain that constant speed. This is used to measure torque which is converted to horsepower. You can have a engine brake dyno connected to the crankshaft, or a wheel dyno connected to the wheel hubs

b. An inertial dyno (such as a Dynojet) uses a drum of known inertia that is accelerated. Based upon the time required to accelerate the drum of known inertia, torque applied to the drum can be calculated and thus horsepower can be easily calculated at the drum as well. In the case of a chassis dyno, a speed sensor is then required to calculate engine torque. Intertial dynos can be engine or chassis dynos as well.

c. An eddy current dyno uses electricity to act much like a brake dyno, except electricity is used instead of water. Once again, and eddy current dyno can be either an engine or chassis (wheels) dyno.

Also a brake dyno does not measure load, but rather applies load to determine torque. Small difference, but important.

Mass of engine components have no impact on horsepower. I'll say that again, engine component mass has no impact on horsepower. But what about low mass pulleys and flywheels you ask? Good question. They will show up as additional horsepower on an inertial dyno, but not on a brake dyno. A brake dyno does not work off acceleration. A brake dyno works by keeping the engine or drivetrain at a constant speed and since nothing is being accelerated, mass has absolutely no bearing.

A manufacturer's claim of net horsepower is SAE Net at the crankshaft. It is not wheel horsepower and I've never seen a manufacturer make any wheel horsepower claims. To measure SAE Net horsepower, you must use an engine brake dyno.
 

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Geo said:


1) Brake horsepower is not the same as SAE Gross

2) SAE Net is definitely not the same thing as wheel horsepower

3) Brake horsepower is measured at the crankshaft and can be either SAE Gross or SAE Net. The difference is that SAE Gross is without driving the accessories (i.e. alternator etc) and intake and exhaust is whatever you want it to be. SAE Net is as delievered from the factory with all accesories driven.
Depending on which literature you used, they each have their own definitions. There is no standardized (consensus or concurrence) definition on the above mentioned terminologies and SAE is trying to accomplish this by setting standards. The information I got came from these standards.

Geo said:

4) Dynos

a. A brake dyno holds the engine to a constant speed using a varying load as necessary to maintain that constant speed. This is used to measure torque which is converted to horsepower. You can have a engine brake dyno connected to the crankshaft, or a wheel dyno connected to the wheel hubs

b. An inertial dyno (such as a Dynojet) uses a drum of known inertia that is accelerated. Based upon the time required to accelerate the drum of known inertia, torque applied to the drum can be calculated and thus horsepower can be easily calculated at the drum as well. In the case of a chassis dyno, a speed sensor is then required to calculate engine torque. Intertial dynos can be engine or chassis dynos as well.

c. An eddy current dyno uses electricity to act much like a brake dyno, except electricity is used instead of water. Once again, and eddy current dyno can be either an engine or chassis (wheels) dyno.
Good info on a variety of dynos.

Geo said:

Also a brake dyno does not measure load, but rather applies load to determine torque. Small difference, but important.
I think you misunderstood the sentence: "so on a dynamometer you apply a load to the floored engine and measure the load the engine can handle at different engine speeds." My understanding of the phrase "...and measure the load the engine can handle at different engine speeds" implies determining torque, as you mentioned. To determine torque you need this applied load times moment arm. The original author might have phrased it differently but it should have been phrased like this "A dynamometer places a load on the engine and measures the amount of power that the engine can produce against the load."
Good pick up.

Geo said:

Mass of engine components have no impact on horsepower. I'll say that again, engine component mass has no impact on horsepower. But what about low mass pulleys and flywheels you ask? Good question. They will show up as additional horsepower on an inertial dyno, but not on a brake dyno. A brake dyno does not work off acceleration. A brake dyno works by keeping the engine or drivetrain at a constant speed and since nothing is being accelerated, mass has absolutely no bearing.
Geo, depending on the dyno you used to measure your horsepower, the mass of pulleys and flywheels might and might not have an impact on the result. You are correct in this respect. But what you fail to comprehend is the mass of the engine internal components, ie, connecting rods, pistons, valves, springs, etc. The mass of the pistons/connecting rods and valves/springs are always a draw on horsepower. PERIOD. So your phrases "Mass of engine components have no impact on horsepower. I'll say that again, engine component mass has no impact on horsepower. " is completely 120% INCORRECT!!!!!!! The dynamic and inertia, ie mass, of these internal components are so critical in engine design that engine design engineer would sacrifice their lives for it!!!! What you are telling me is that for the same volume of combustible gas to move a, say, 5 kg piston is the same to move a 1 kg piston? You might want to rethink this...

Geo said:

A manufacturer's claim of net horsepower is SAE Net at the crankshaft. It is not wheel horsepower and I've never seen a manufacturer make any wheel horsepower claims. To measure SAE Net horsepower, you must use an engine brake dyno.
Again, RE: definitions of these terms, I'm not going into it. My comments remain the same as the above. But yes, I agree that I've never seen any manufacturer make any claims for wheel horsepower mainly because of marketting purposes. The reasons the industry avoid using wheel horsepower is because of the cost associated with the dyno testing. It is also a lot cheaper and easier to get the geek engineer with HUGE goggles to do some number crunching than to put the car on a dyno!
 

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G-loads said:
Depending on which literature you used, they each have their own definitions. There is no standardized (consensus or concurrence) definition on the above mentioned terminologies and SAE is trying to accomplish this by setting standards. The information I got came from these standards.
SAE defined SAE Gross and SAE Net almost 30 years ago. The definitions are most definitely specific.

G-loads said:
Geo, depending on the dyno you used to measure your horsepower, the mass of pulleys and flywheels might and might not have an impact on the result. You are correct in this respect. But what you fail to comprehend is the mass of the engine internal components, ie, connecting rods, pistons, valves, springs, etc. The mass of the pistons/connecting rods and valves/springs are always a draw on horsepower. PERIOD. So your phrases "Mass of engine components have no impact on horsepower. I'll say that again, engine component mass has no impact on horsepower. " is completely 120% INCORRECT!!!!!!!


No, I'm afraid it is you who is incorrect. Component mass has no impact on hp. Mass affects acceleration, and thus it appears to affect hp on an inertial dyno, but the reality is it has zero effect on hp. Low mass components simply allow the engine to rev more quickly. They improve acceleration, but do not affect hp.

G-loads said:
The dynamic and inertia, ie mass, of these internal components are so critical in engine design that engine design engineer would sacrifice their lives for it!!!!
Yes they will - but because the engine will rev more quickly. It does not increase hp.

G-loads said:
What you are telling me is that for the same volume of combustible gas to move a, say, 5 kg piston is the same to move a 1 kg piston? You might want to rethink this...
Don't confuse the effect of mass on acceleration with production of power.

Are you saying that if I reduce the mass of my car by 100kg I've increased the hp? No, of course not.

G-loads said:
But yes, I agree that I've never seen any manufacturer make any claims for wheel horsepower mainly because of marketting purposes. The reasons the industry avoid using wheel horsepower is because of the cost associated with the dyno testing. It is also a lot cheaper and easier to get the geek engineer with HUGE goggles to do some number crunching than to put the car on a dyno!
Uh, hp numbers quoted by manufacturers are not done by some geek with a calculator. They are crunched on a dyno. If you think that OEMs don't do extensive dyno testing, I've got a bridge to sell you. They use dynos for more than just calculating hp.
 

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Re: woa!!!

Chris said:
You guys are getting way to into this....

Can't we just enjoy our cars for what they are and not talk about the HP rating?:paranoid:

Some people participate beause they want to talk and that's OK.

Some people participate because they want to teach/learn and that's OK too.

=)
 

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Yeah after I read the post, my brain fried. Arrrgghhhhhhh!!!!!!
 

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Mista McCoilover said:
Yeah after I read the post, my brain fried.

Oh yummy......


Got any ketchup to go with that? :eek:

;)
 

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Discussion Starter #18
I really want to thank you guys for all the info! After i read it a second and third time i've got a much better idea about what's goin on. And i also never new we had so many Bill Nyne's runnig around on the forum:beard: :asian: :beard:
 

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Geo said:

No, I'm afraid it is you who is incorrect. Component mass has no impact on hp. Mass affects acceleration, and thus it appears to affect hp on an inertial dyno, but the reality is it has zero effect on hp. Low mass components simply allow the engine to rev more quickly. They improve acceleration, but do not affect hp.
Overall mass has an overall effect on vehicle acceleration. No doubt. Component mass has an impact on hp mainly because of the mass moment inertia. Mostly reduces hp if heavy, or gains hp if light. The number is so small that it is neglegible but it does have an impact. Recall the two equestions:

Linear Power = (Force)(Distance)/Time
Horsepower = 550(ft)(lb)/s

Rotational Power = (Torque)(RPM)
Horsepower = (Torque)(RPM)/5252

"Low mass components simply allow the engine to rev more quickly" you said? Look at the "RPM" term. Clearly, there is a direct relationship between acceleration and horsepower.


Geo said:

Yes they will - but because the engine will rev more quickly. It does not increase hp.
Of course it will not increase hp. I never implied that. My simple point I want to make is that the mass of internal components will contribute to the hp, either loss or gain. Period.


Geo said:

Don't confuse the effect of mass on acceleration with production of power.

Are you saying that if I reduce the mass of my car by 100kg I've increased the hp? No, of course not.
You are talking about the whole car. I am talking about inside a cylinder. Acceleration is dependent of production of power. See above equations.

Geo said:

Uh, hp numbers quoted by manufacturers are not done by some geek with a calculator. They are crunched on a dyno. If you think that OEMs don't do extensive dyno testing, I've got a bridge to sell you. They use dynos for more than just calculating hp.
I would not say they completely avoid using DYNOS, but certainly would reduce the cost in any means they can. An engineer with adequate info on the engine can get the hp better and faster than a dyno. Of course the number you obtained from a dyno will likely be different than the one an engineer calculated simply because of loss from a dyno test.

PS It's always nice to debate ,so long you respect the opinion of your adversary. :D
 

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G-loads said:
Overall mass has an overall effect on vehicle acceleration. No doubt. Component mass has an impact on hp mainly because of the mass moment inertia. Mostly reduces hp if heavy, or gains hp if light. The number is so small that it is neglegible but it does have an impact.
It's going to be immeasurable. It's going to be the difference in the energy used to accelerate the piston and the energy imparted to the crankshaft.

G-loads said:
Clearly, there is a direct relationship between acceleration and horsepower.
But the engine itself is not accelerating on the dyno. It's turning at a constant rpm (brake dyno).

G-loads said:
Of course it will not increase hp. I never implied that. My simple point I want to make is that the mass of internal components will contribute to the hp, either loss or gain. Period.
I don' know if it's a typo here or poor quoting, but you are contradicting yourself.

G-loads said:
You are talking about the whole car. I am talking about inside a cylinder. Acceleration is dependent of production of power. See above equations.
What we are talking about is differences in the say power is being measured, i.e. brake dyno vs. inertial dyno. Low mass components don't make horsepower. They just accelerate more quickly. You are not increasing the horsepower, but rather reducing the mass you are accelerating. So, on the inertial dyno it appears you are making more hp, but you are really accelerating less mass.

That said, it's a useful number to know, but is it really a correct measure of hp? Again, I suggest not since you won't see it on a brake dyno since the engine is not accelerating, but rather running at a constant rpm.

G-loads said:
I would not say they completely avoid using DYNOS, but certainly would reduce the cost in any means they can. An engineer with adequate info on the engine can get the hp better and faster than a dyno. Of course the number you obtained from a dyno will likely be different than the one an engineer calculated simply because of loss from a dyno test.
OEMs do extensive dyno work. How do you think they develop an engine? They don't necessarily use them to measure hp, but to make them reliable, efficient, etc. I think you're thinking too narrowly here.

G-loads said:
PS It's always nice to debate ,so long you respect the opinion of your adversary. :D
I think I'm showing you respect. However, don't confuse opinions with fact. What we are talking about is facts and one or both of us are wrong. I've got one of the definitive books on internal combustion engines at home. I'll try to find appropriate information and post it. I forgot to last night.
 
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