Over the years the car manufacturers have rated the horsepower of their engines differently.
As far as I am aware the current method is to measure the horsepower at the crankshaft using the SAE standard. Hower there are three standards that can be applied, SAE gross HP. SAE Net HP and SAE Certified HP In the 50's and 60's the auto manufacturers developed a system called BHP or brake horsepower. This method of measurement was a good marketing ploy as the numbers were always higher than the SAE numbers. The there is the common method that racers use that is RWHP or rear wheel horsepower. This is an accurate and consisitent horsepower measurement technique as it takes into consideration drivetrain losses and gives you the HP number to the ground.
Point is that with all of the ways to measure horsepower who knows what we are really getting from the automakers these days? Does anyone know how the automakers rate their engines and what methods they apply to rate horsepower? I believe that the method must be consistent but does anyone know for sure?

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, 3.4" Pulley, N* TB, LS1 MAF, Flotech Exhaust Autolite 104's Custom CAI 4T65eHD w. custom axles, HP Tuners VCM Suite.
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[This message has been edited by Dennis LaGrua (edited 08-15-2009).]

Good question. I'm not sure that there is any consistency in how the manufacturers rate horsepower.

A quick look at GM's powertrain site shows that just about every engine, except those for SAAB and a few others, are SAE certified: http://media.gm.com/us/powe...vices/2009/09car.htm

I believe that GM rates engines using an engine dyno, not a chassis dyno - otherwise you'd expect a larger difference between 2 and 4WD or automatic and manual options listed on the site.

I haven't looked at other manufacturers, but since I don't plan on purchasing another vehicle from "government motors" it might be time to check out what vehicles have the new ecoboost engine from Ford

Cheers

http://www.hotrod.com/techa...ock_build/index.html

quote In the world of dyno-testing, there are two main correction factors used to standardize results with varying atmospheric conditions: SAE J-1349, which adjusts the prevailing test conditions to 77-degree-F ambient air temperature and 29.92 in-Hg barometric pressure; and SAE J-607 (also known as Standard Temperature and Pressure), which corrects the test data to 60-degree-F air and 29.23 in-Hg barometric pressure. Most OE manufacturers use SAE J-1349 to rate engine output, and those numbers are always given as flywheel horsepower. Most magazines, race-engine builders, and aftermarket companies use STP correction factors when quoting dyno horsepower figures, and the difference between the numbers generated by each is generally about 5 percent of the output as a result of the STP factor correcting to colder air. Interestingly, in its stock, baseline configuration, the LS2 made exactly 400 hp at 6,000 rpm and 398 lb-ft of torque at 4,400 using the SAE J-1349 factor, right on par with its official GM rating. Converting to STP correction numbers equates to 422 hp and 418 lb-ft. That's a substantial difference, but the point we want to make is that GM is not underrating its engines, it's just rating them differently than most magazine readers are used to seeing.

http://www.sae.org/certifiedpower/details.htm

quote SAE Engine Rating Standard Prevents Numbers Fudging General Motors has become the first manufacturer to certify an engine's power and torque ratings using a newly adopted SAE standard (J2723), James Queen, GM Vice President, Global Engineering, announced during his keynote address at the SAE World Congress and Exhibition in April 2005. The world's largest automaker plans to certify all of its engines to the voluntary standard, and is encouraging its competitors to do the same. The LS7 engine for the 2006 Chevrolet Corvette Z06 was certified under the new standard this month. The 7.0-L V8 unit produces 505 hp (377 kW) at 6300 rpm and 470 lboft (637 Nom) at 4800 rpm. "The new voluntary SAE power and torque certification procedure ensures fair, accurate ratings for horsepower and torque as it uses third-party certification," said Queen. "SAE technical standards level the playing field, and this certification procedure is just the latest example of the value SAE has offered over the past century." To tout power and torque ratings as "SAE-certified," engine manufacturers must have an SAE qualified witness watch over the entire testing procedure to ensure that it is conducted in conformity to SAE standard J1349. Third-party witnessing is the main provision of J2723. An existing SAE standard, J1349, spells out how the actual testing is to be done. J1349 was updated last year to eliminate some ambiguities that allowed engine makers to cite power and torque ratings higher than the engine's actual capabilities. Engine makers are free to cite power and torque figures drived from testing conducted outside the scope of the SAE standards, but they may not claim the figures are SAE-certifed. "We feel that both the consumer and industry are well served by having accurate, consistent ratings from all manufacturers," said David Lancaster, a Technical Fellow in GM Powertrain and Chairman of the SAE Engine Power Test Code Committee that updated J1349 and wrote J2723. Data from a wide array of parameters (e.g., air:fuel ratio) will be collected during testing conducted to the SAE standards. SAE will create a database and offer it to industry in different packages and at different price points.

[This message has been edited by Formula88 (edited 08-16-2009).]

"Brake HP" is just horsepower measured on a brake dyno, as opposed to an inertial dyno OR calculated from measured pressures ("indicated"). "Brake" doesn't just apply to horsepower, as the distinction between brake and indicated can be made for virtually any engine parameter. The difference between IMEP and BMEP, for instance is the specific torque required to overcome the engine's internal parasitic losses.

Chassis dynos results vary wildly from one dyno to the next and even moreso among different types of chassis dynos. They are neither accurate nor consistent. The only way to achieve consistent results is to dyno the same car on the same dyno with the same calibration. Other than that, it's a crap shoot.

Horsepower in itself is an inaccurate measurement IMO.

You know it was originally concieved (and is still derived from) the ability of the creator's horse to lift a 1lb load 1ft in the air utilizing a tree branch as a lever?

Horsepower is also simply a measurement of torque,so when you get down to it who cares about horsepower-gimme torque
It's all just numbers anyway-it only takes a moment of inaction from someone with a 600hp car to get beat by someone with a 400hp car at the track.
And so many other factors come into play such as suspension,driving style etc.. determining how fast and/or quick a car is.

quote Originally posted by Dennis LaGrua:...The there is the common method that racers use that is RWHP or rear wheel horsepower. This is an accurate and consisitent horsepower measurement technique as it takes into consideration drivetrain losses and gives you the HP number to the ground. ...

Dennis, from what I've read in many articles about chassis dyno tests you have to use the same dyno to check modifications that are made to the engine to have valid data on what the affect of the change was. Moving to a different dyno would make any results suspect due to variabilities between dynos. No two dynos are necessarily the same. I've read that the actual horsepower number can have a fairly high tolerance (+/- some number of horsepower), only the relative change in horsepower is of use in tuning. How well the ambient atmosphere conditions (temperature, humidity, altitude) are controlled can play hell with the numbers also, so time of day changes may affect these.

I've read that SAE requires parasitic standard equipment be operating on the engine when these tests are run (power steering, water pump, etc)


http://www.edmunds.com/insi...ews/articleId=106965

http://en.wikipedia.org/wik...power#SAE_horsepower

http://www.caranddriver.com...nd_resolution-column
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RickN
White 88GT 5spd
White 85GT Auto
White 99 F250SD 7.3PSD 6spd
1956 Ford 860 Tractor w/ Freeman Loader
20Ft Tilt Bed Trailer

[This message has been edited by RickN (edited 08-16-2009).]

Some quotes from my favorite book
Motor Service's Automotive Encyclopedia.

"POWER
Power is defined as the rate or speed at which work is performed. One horsepower is defined as the amount
doing 33,000 ft.lbs. of work in one minute.
The unit of measurement was originated by an engineer by the name of Watt,who found that a strong horse could hoist 366lbs
of coal up a mine shaft at the rate of one foot per second. In one minute,the horse would have raised the 366lbs. 60ft.
This would be equivalent to raising 21,960lbs., one foot in one minute.
Arbitrarily,Mr. Watt raised this figure to 33,000lbs. one foot in one minute.
Expressed as a formula
[code] ft.lb. per min DW
HP= ----------- = -------
33,000 33,000 t [code/]

Where
D= the distance in the weight is to be moved
W=Force in pounds required to move the weight through that distance.
t= time in minutes required to move the weight through the distance D
RATED HORSEPOWER
The Rated horsepower of an engine is based on a formula developed in the early days of the industry
and is based on the assumption of a brake mean effective pressure of 67.2psi and a piston speed of 1000 FPM (not RPM)
Todays's engines operate at much higher speeds and pressures and consequently the formula no longer
gives any indication of the power output of an engine. (and this is circa 1970!)

It is often incorrectly referred to as the SAE horsepower,but the correct name is rated or AMA horsepower after an
automotive association which is no longer in existance. However,the forumula is still used for purposes of
licensing automotive vehicles.
[code] Rated horsepower= 6 x 4 x 4
----------- = 38.4
2.5
[code/]
"

I always found that stuff interesting,figured I would throw it up.
I'm friends with the owner of the local dyno shop,do some tuning now and then for him.
Every dyno is different,they all read different. It's no more than an indicator imo.
Fast or powerful is all relative really.
Hope this info helps or educate's-it's easily my favorite and oldest book.
Funny,don't think things have changed much in 40 years.
It also has the definitions for indicated and brake horsepower among other interesting things.
I can type them up if anyone is interested.

*Sorry,couldn't figure out how to get the formula's right.

[This message has been edited by DefEddie (edited 08-16-2009).]

quote Originally posted by DefEddie: Horsepower in itself is an inaccurate measurement IMO. You know it was originally concieved (and is still derived from) the ability of the creator's horse to lift a 1lb load 1ft in the air utilizing a tree branch as a lever? Horsepower is also simply a measurement of torque,so when you get down to it who cares about horsepower-gimme torque

Horsepower is not merely a measure of torque, but of torque over time. Your opinion of it isn't really important, it is accurate, it is very real, and it makes for very real differences in performance. And it wasn't just to lift a 1lb load in the air 1ft, it was a 550lb load 1 ft in 1 second. Please read http://www.vettenet.org/torquehp.html

[This message has been edited by crazyd (edited 08-17-2009).]

"Awhile back, a gentleman by the name of Watt (the same gent who did all that neat stuff with steam engines) made some observations, and concluded that the average horse of the time could lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 foot pounds per second, or 33,000 foot pounds per minute, for an eight hour shift, more or less. He then published those observations, and stated that 33,000 foot pounds per minute of work was equivalent to the power of one horse, or, one horsepower. "

33,0000 ftlb's per minute = one horsepower?
That's what I said wasn't it?

Horsepower = torque x RPM / 5252

Horsepower might not be an actual function of torque but look's pretty clear that horsepower is a measurement of torque.


"First of all, from a driver's perspective, torque, to use the vernacular, RULES "
"Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same"

Not trying to debate,but the link seems to agree with me (a driver) that torque rules.

Torque is a torsional measurement-it's what get's you there.
Horsepower is how long you can keep it there pretty much.

I only wanted to point out that dyno's and power measurements are not exact.

Torque is measured.
Horsepower is derived.

Kevin

[This message has been edited by Lambo nut (edited 08-17-2009).]

Horsepower is a function of TWO variables, BOTH of which need to be measured.

Formula 1 engines push just a touch over 200 ftlbs to 19,000 to produce over 700 HP out of 2.4 litres.
The PT6A in a T34 (turbine) produces ~100 ftlbs at 33,000 RPM...

...Buuuut that 100 ftlbs at 33,000 RPM gets geared down to 1500 ftlbs at 2200 RPM to drive the prop.
The largest piston engines used on ships engines produce 101,000 HP at 101 RPM by developing 5 *million* ftlbs.
However, most Navy ships are driven by gas turbines that turn 10,000 RPM or so, while the screw RPM is less than 250. Shaft horsepower is in the 30K-60K range.
In Aircraft carriers, steam turbines drive about 80K horsepower to each of FOUR screws, again turning less than 250 RPM or so.

So the nature of the application needs to dictate what the best power band characteristics are. You can't say that an engine with low RPM torque is always best, or vice versa. Even the RPM ranges of diesel engines have been climbing dramatically this decade. You can buy diesels that turn over 5,000 RPM nowadays.

that is why there are multiple methods to rate
if you are bothered by HP's ratings - the easy answer is:
1/4 mile time
skip potential, and go straight to results

as long as there is a need to BS, there will be new ways to confuse established rating systems

The turbine deal is interesting will.
But your talking about gearing and drive ratio's then-and that is a different subject from the core engine power.
Dropping to a lower gear ratio in your truck may make the truck quicker but you've not changed horsepower any.
Raising it will make you faster,but still doesn't change horsepower/torque either.
Of course doing the same thing internally with rod/stroke ratio would be concieved as changing the core power as it's an
internal engine modification.
But when you get down to it,the core hp/tq goes back to actual cylinder and combustion dynamics which goes into thermal and volumetric efficiency etc..
and on and on and on...

hp/tq is always an interesting topic.
"I just wanna go fast"
If your not an engineer trying to push something to a exceed a given limit then who really cares?
I'm not even close to an engineer,the only thing i'm an expert on is my own opinion.

quote Originally posted by DefEddie: 33,0000 ftlb's per minute = one horsepower? That's what I said wasn't it?

No. You said it was to lift 1 pound 1 foot from a tree branch. That is only a measure of torque. Factor in time and then you have a measure of horsepower.

quote Horsepower = torque x RPM / 5252 Horsepower might not be an actual function of torque but look's pretty clear that horsepower is a measurement of torque.

No. Horsepower is how much torque is produced for a given time or rate. In the case of an engine it is how much torque is produced at a specific RPM. A horsepower rating is the peak number at a specific RPM that an engine achieves over its operating RPM range. It does not necessarily coincide with its torque peak and does not fully characterize an engine's performance over its operating RPM range because it is only a snapshot of its power at a single RPM. But it does still matter.

quote "First of all, from a driver's perspective, torque, to use the vernacular, RULES " "Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same" Not trying to debate,but the link seems to agree with me (a driver) that torque rules. Torque is a torsional measurement-it's what get's you there. Horsepower is how long you can keep it there pretty much.

No. Horsepower is how quickly you get there, because it is expressed as a function of time. You missed the most important quote of all, which is "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*."