gross hp vs. net hp vs rear wheel hp revisited
sven...@my-dejanews.com
any. I just happened to come across an answer while looking through edmunds
site of all places. Here it is:
" The disparity between these two figures comes from the fact that one is a
gross horsepower rating and the other is a net horsepower rating. Gross
horsepower is a measurement of engine output, taken at the flywheel, without
the engine installed in a vehicle. Since the engine has no load on it, all of
its energy can be used for making horsepower.
Net horsepower, by comparison, is a measurement taken at the driven wheels of
a vehicle on what’s called a dynamometer. This is done by placing the
vehicle’s driven wheels on a large roller and accelerating the wheels up to
redline in first or second gear. The vehicle’s ability to turn this roller is
measured and calculated to come up with a figure that represents how much
horsepower is actually available to move the vehicle around. Because a
frictional loss between the engine and the driven wheels is unavoidable, net
horsepower will always be less than gross horsepower. "
The rest of the article can be viewed at:
http://www.edmunds.com/edweb/editorial/tech/horsepower.html
Sven
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Erich Coiner
>
> A while back the question was asked about the difference between the three, if
> any. I just happened to come across an answer while looking through edmunds
> site of all places. Here it is:
>
> " The disparity between these two figures comes from the fact that one is a
> gross horsepower rating and the other is a net horsepower rating. Gross
> horsepower is a measurement of engine output, taken at the flywheel, without
> the engine installed in a vehicle. S
> a vehicle on what’s called a dynamometer. This is done by placing the
> vehicle’s driven wheels on a large roller and accelerating the wheels up to
> redline in first or second gear. Th
>
> -----------== Posted via Deja News, The Discussion Network ==----------
> http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
You have only covered two of the three measurements of horsepower.
You got gross, which is what was advertised by the automakers prior to
1972.
You got rear wheel net horsepower. Measured by a wheel dyno.
You missed SAE net horsepower. This is what all car manufacturers
advertise since 1972.
This horsepower is measured at the flywheel. All of the engines
accessories are installed and driven by belts but they are not operating
under load. What this means is the alternator is not trying to charge a
battery and the powersteering pump is not moving the rack.
The SAE net horsepower IS NOT measured at the rear wheels (or front on
FWD). If you notice Ford does not rate the 4.6L as having different
horsepower when equipped with 5speed or automatic.
We all know the automatic sucks up horsepower and is much less efficient
than the 5 speed. If they were reporting rear wheel horsepower, the auto
would have a lower rating. They don't and the reason is the horsepower
is taken at the flywheel and not the wheels.
QED
Erich
Mark Kovalsky
sven...@my-dejanews.com wrote in message
<71lgvv$5ih$1...@nnrp1.dejanews.com>...
>A while back the question was asked about the difference between the three,
if
>any. I just happened to come across an answer while looking through
edmunds
>site of all places. Here it is:
There it was. Edmund's apparently has no clue.
Gross horsepower is a fictional number. It is the amount of total horsepower
an engine produces, including the amount of power used to overcome friction
inside the engine. Nobody can get gross horsepower because a frictionless
engine has never been made.
Gross horsepower can be measured, if you have a motoring dyno. Use the
dyno to spin the engine, without fuel or spark. Measure the amount of
horsepower used to turn the engine. This is the frictional horsepower.
Now run the engine and measure it's output. Adding these two numbers
together gives gross horsepower.
Net horsepower is gross horsepower minus the friction horsepower. This is
the amount of power that an engine dyno reads.
SAE net horsepower is net horsepower measured under conditions specified
by the SAE (Society of Automotive Engineers.) SAE specifies that all
accessories
are on the engine, such a power steering, A/C, alternator, engine fan, if so
equipped, etc. None of it is operating, but it's there and the belts are,
too. The
engine also will have the air cleaner and a vehicle exhaust, or an orfice to
duplicate
the exhaust system backpressure. This horsepower is also measured at the
flywheel.
Rear wheel horsepower is just that. It is measured on a chassis dyno, not an
engine dyno.
All automotive companies advertise SAE net horsepower. It's the industry
standard.
Mark Kovalsky, P. E.
WindsorLX
SVO23turbo wrote:
> >From: "Mark Kovalsky"
>
> >All automotive companies advertise SAE net horsepower. It's the industry
> >standard.
>
> Yes it is and thank goodness it is.
No way!! I think they should post RW hp. Maybe if they posted both.
BEcause a 5.0 is a 5.0, I bet the RWHP is lower on an Explorer than on a
Mustang.
WindsorLX
Mark Kovalsky wrote:
> All automotive companies advertise SAE net horsepower. It's the industry
> standard.
>
> Mark Kovalsky, P. E.
So how does this relate to Brake Horse Power, or is that an old name for rear
wheel horse power??
WindsorLX
WindsorLX
WindsorLX
Erich Coiner wrote:
> > So how does this relate to Brake Horse Power, or is that an old name for rear
> > wheel horse power??
>
> A brake is an old term for a dynomometer. So brake horsepower is
> horsepower measured on a dyno. It could be gross, or SAE net. It is not
> likely to be rear wheel horsepower because I don't think people call a
> chassis dyno a "brake".
>
> I guess the real answer is brake horsepower is not specific enough term
> to have real meaning.
>
> Erich
I was thinkink bbrake as if it had something to do with the car brakes. You exp.
sounds more plausible though. I have an old book which lists all cars produced in
the worl in 1957 or 58, and in all cases it lists "BHP" or brake horse power.
ASmall9494
>A while back the question was asked about the difference between the three,
>if
>any. I just happened to come across an answer while looking through edmunds
>site of all places. Here it is:
>
>" The disparity between these two figures comes from the fact that one is a
>gross horsepower rating and the other is a net horsepower rating. Gross
>horsepower is a measurement of engine output, taken at the flywheel, without
>the engine installed in a vehicle. Since the engine has no load on it, all of
>its energy can be used for making horsepower.
>
>Net horsepower, by comparison, is a measurement taken at the driven wheels of
>a vehicle on what’s called a dynamometer. This is done by placing the
>vehicle’s driven wheels on a large roller and accelerating the wheels up to
>redline in first or second gear. The vehicle’s ability to turn this roller is
>measured and calculated to come up with a figure that represents how much
>horsepower is actually available to move the vehicle around. Because a
>frictional loss between the engine and the driven wheels is unavoidable, net
>horsepower will always be less than gross horsepower. "
>
>The rest of the article can be viewed at:
>
>http://www.edmunds.com/edweb/editorial/tech/horsepower.html
>
>Sven
Not to be overly rude, but Edmunds is wrong. Don't go to them for much. They
know less about autos than consumer reports. Their definition of net hp is an
accurate description of rear wheel hp. Rear wheel hp is less than net hp. Net
hp is less than gross hp. Net and gross are both determined at the flywheel.
Go to your local bookstore and read some automotive tech. Don't count on
Edmunds for anything but those cutesy little star ratings like consumer
reports. These people give car enthusiasts very bad information. Its the
equivalent of taking your car to a dealer and paying them $150 just to run a
diagnostic. If you are willing to do such ludicrous things, they'll take you
for every penny you have and then some. The best thing anyone can do is
educate themselves about their cars. It really pays to know more than the
dealer and the mechanic thinks you know. You'll save yourself lots of money
and not fall victim to such incorrect information. Go to www.datsuns.com, Dave
some great info on net, gross, and rear wheel hp and how mods affect hp, his
information is correct which leads me to believe Dave is reading the correct
books.
Anthony TBA #2
'97 Cobra #301, '85.5 - '86 SVO wanted
<a href="http://members.aol.com/asmall9494/index.html">My Cobra Page</a>
<a href="http://members.aol.com/SVO23turbo/index.html">My SVO Page</a>
member ramfm since 1/21/98
ASmall9494
>You have only covered two of the three measurements of horsepower.
>You got gross, which is what was advertised by the automakers prior to
>1972.
>You got rear wheel net horsepower. Measured by a wheel dyno.
Lets call it rear wheel hp to eliminate confusion and be more precise.
>You missed SAE net horsepower. This is what all car manufacturers
>advertise since 1972.
>This horsepower is measured at the flywheel. All of the engines
>accessories are installed and driven by belts but they are not operating
>under load. What this means is the alternator is not trying to charge a
>battery and the powersteering pump is not moving the rack.
>The SAE net horsepower IS NOT measured at the rear wheels (or front on
>FWD). If you notice Ford does not rate the 4.6L as having different
>horsepower when equipped with 5speed or automatic.
>We all know the automatic sucks up horsepower and is much less efficient
>than the 5 speed. If they were reporting rear wheel horsepower, the auto
>would have a lower rating. They don't and the reason is the horsepower
>is taken at the flywheel and not the wheels.
Lets call this net hp for the same reason.
SVO23turbo
>All automotive companies advertise SAE net horsepower. It's the industry
>standard.
Yes it is and thank goodness it is.
Anthony TBA#2
YZ250Racer
>Anthony TBA #2
>'97 Cobra #301, '85.5 - '86 SVO wanted
><A HREF="http://members.aol.com/asmall9494/index.html">My Cobra Page</A>
><A HREF="http://members.aol.com/SVO23turbo/index.html">My SVO Page</A>
>member ramfm since 1/21/98
You can't find one? Here are a few....
1986 Mustang SVO, orig. owner, 51k miles, Eibach springs, Koni shocks, ROH
wheels, new tires, Borla mufflers, garaged until recently, car cover, have all
orig. parts, wheels and tires, one nice ride, 304-524-2527 (red)
1986 SVO, absolutely flawless, CA, garaged collectible, 44k orig. miles, highly
detailed, 9 trophy winner, 2nd owner, never in rain, no leaks or squeaks,
beautiful origional paint, great driver, exc. investment, $8,500, 760-320-2573
(white)
1986 SVO Mustang white/grey lthr., 49k miles, 1 owner, all orig. equipment,
sored last 9 years, exc. cond., $8295, ph.-614-529-9992, fax-614-529-9925, OH
Mustang: 1986 SVO, jalapeno red, leather, 40k, stored winters, 1996 SAAC
Councours winner, $8,950 obo., trades, 518-272-5597, NY.
Mustang: 1986 SVO, blk., cloth int., 18k miles, orig. owner, never modified,
abused, raced, kept garaged, covered, CA emissions, shop manuals, bra, $9k,
Steve - 541-582-3672
1986 Mustang SVO, charcoal grey, grey lthr., all power, 37k miles, from CA,
never in snow or salt, exc. cond., always garaged, cover, shop manuals,
security system, spare set SVO wheels w/BFG R1s, $10,200, 248-922-9810
1985 1/2 Mustang SVO Competition Prep. option, black, grey lthr., 379 miles., 1
of 10 comp. prep., possibly lowest mileage SVO cpe. in existence, museum
quality, $30,000 obo, Joe, days-508-384-8000, nights-508-668-2909
I don't know where you live, or if you mind buying out of state, but maybe you
live in one of these places... (If you want to see these listings, just pick
up a copy of Mustang & Ford Trader.)
Nicholas, 2 '94 YZ250s, 1995 Trans Am/M6/TT/red,
1992 Grand Prix (soon to be replaced by a '95 Mustang GT)
"Beware! I'm underage and overeducated."
You want to put some money on this game? Sure thing. I break... :-)
SVO23turbo
>You can't find one? Here are a few....
>
>$8,500,
>$8295,
> $8,950 obo.,
>$9k,
>$10,200,
>$30,000 obo
>I don't know where you live, or if you mind buying out of state, but maybe
>you
>live in one of these places... (If you want to see these listings, just pick
>up a copy of Mustang & Ford Trader.)
No, but at those prices, I sure won't be looking to buy one from the Ford
trader.
Anthony TBA#2
<a href="http://members.aol.com/SVO23turbo/index.html">My SVO Page</a>
<a href="http://members.aol.com/asmall9494/index.html">My Cobra Page</a>
member ramfm since 1/21/98
Erich Coiner
> > Rear wheel horsepower is just that. It is measured on a chassis dyno, not an
> > engine dyno.
> >
> > All automotive companies advertise SAE net horsepower. It's the industry
> > standard.
> >
> > Mark Kovalsky, P. E.
Erich Coiner
>
> SVO23turbo wrote:
>
> > >From: "Mark Kovalsky"
> >
> > >standard.
> >
>
> BEcause a 5.0 is a 5.0, I bet the RWHP is lower on an Explorer than on a
> Mustang.
On that explorer would that be 2wd or 4wd? 4wd with 4wd engaged or not?
Automatic or manual transmission. All of these combos would need to be
quoted.
I guess is 4wd was engaged you would need a dyno on both axles to
measure the hp. Sounds like a pain to me.
The system the way it is works. It is a good system.
Erich
Mark Kovalsky
WindsorLX wrote:
> So how does this relate to Brake Horse Power, or is that an old name for rear
> wheel horse power??
Brake Horsepower is an obsolete term that was the same as Gross Horsepower.
--
Mark
---------------------------------------------------
'30 Ford Model "A" Tudor '98 Ford Taurus
'59 Edsel Corsair '99 Mercury Cougar
'94 Ford Club Wagon 7.3L Diesel with Hypermax Turbo
'98 SunnyBrook 33' Travel Trailer
---------------------------------------------------
The views expressed above are mine, and mine alone.
sven...@my-dejanews.com
mkov...@prodigy.net wrote:
>
>
> WindsorLX wrote:
>
> > So how does this relate to Brake Horse Power, or is that an old name for
rear
> > wheel horse power??
>
> Brake Horsepower is an obsolete term that was the same as Gross Horsepower.
>
Brad Swidzinski
I don't care what you say to complicate this. Gross hp, as described by
every American car maker and auto mag, has ALWAYS been the horsepower
generated by the engine without accessories (power steering) or drivetrain,
that is, at the fly wheel! For a fictional number, Ford managed to get
225gross for my '67 289 and 225net for my '91 5.0. Go figure.
Brad
Mark Kovalsky wrote in message
<71ltas$8qs4$1...@newssvr04-int.news.prodigy.com>...
>
>sven...@my-dejanews.com wrote in message
><71lgvv$5ih$1...@nnrp1.dejanews.com>...
>>A while back the question was asked about the difference between the
three,
>if
>>any. I just happened to come across an answer while looking through
>edmunds
>>site of all places. Here it is:
>
>Rear wheel horsepower is just that. It is measured on a chassis dyno, not
an
>engine dyno.
>
>All automotive companies advertise SAE net horsepower. It's the industry
>standard.
>
>Mark Kovalsky, P. E.
>
>
Mark Kovalsky
Brad Swidzinski wrote:
> Better fill in Road and Track and Car and Driver.
>
> I don't care what you say to complicate this. Gross hp, as described by
> every American car maker and auto mag, has ALWAYS been the horsepower
> generated by the engine without accessories (power steering) or drivetrain,
> that is, at the fly wheel! For a fictional number, Ford managed to get
> 225gross for my '67 289 and 225net for my '91 5.0. Go figure.
In 1972 the automakes stopped using gross horsepower and started
reporting net horsepower.
If you were to take your '67 289 and put the engine on a dyno it
would not make 225 horsepower. You would need to measure the
frictional horsepower and add it to the horsepower measured at
the flywheel to come up with 225 gross. That's why I said it is
a fictional number. You can't put an engine on a dyno and directly
measure gross horsepower.
If you put your '91 5.0L on a dyno with complete air intake, car
exhaust, and all front end accesories ona dyno, it will make 225
net horsepower. If the results are corrected to the SAE standard
air pressure and temperature you would have SAE net, which is
the 225 HP that Ford advertises.
Nobody reports gross horsepower anymore. Not even Road &
Driver :-)
SVO23turbo
>If you were to take your '67 289 and put the engine on a dyno it
>would not make 225 horsepower. You would need to measure the
>frictional horsepower and add it to the horsepower measured at
>the flywheel to come up with 225 gross. That's why I said it is
>a fictional number. You can't put an engine on a dyno and directly
>measure gross horsepower.
>
No if you took your '67 motor put it on the dyno and yanked all the accessories
force fed water to cool it from an external pump, yanked the air intake off,
put a stack on the carb, and put tuned length pipes after the exhaust manifolds
you'd get gross hp.
Mark Kovalsky
SVO23turbo wrote:
> No if you took your '67 motor put it on the dyno and yanked all the accessories
> force fed water to cool it from an external pump, yanked the air intake off,
> put a stack on the carb, and put tuned length pipes after the exhaust manifolds
> you'd get gross hp.
No you wouldn't. Gross horsepower includes the power the engine produces to
overcome it's internal friction.
SVO23turbo
>SVO23turbo wrote:
>
>> No if you took your '67 motor put it on the dyno and yanked all the
>accessories
>> force fed water to cool it from an external pump, yanked the air intake
>off,
>> put a stack on the carb, and put tuned length pipes after the exhaust
>manifolds
>> you'd get gross hp.
>
>No you wouldn't. Gross horsepower includes the power the engine produces to
>overcome it's internal friction.
>
No it does not. Gross hp is measured the way I described that's why the SAE
stepped in and said it was bogus and strongly recommended that auto makers use
net hp instead.
You are describing flywheel hp and adding frictional hp to it as gross hp.
I've never seen this mentioned anywhere. On top of that it has very little use
since the frictional loses of an engine can vary widely. Why on Earth would
someone choose to use such an ambiguous system? I doubt they would hence the
whole reason gross hp was dropped. You could no doubt measure the frictional
hp it takes to spin an engine a certain rpm, but its meaningless in
relationship to that engines output. Output is all that is cared about. Gross
hp is hp output with few specific concerns. Think of it as an engines ideal
output. Net hp is the output the engine makes with the accessories in place,
the exhaust in place, and the induction system in place as mounted in the car
including the air silencer and things of this nature. Please go read the SAE
handbook or some automotive books at your local bookstore. It amazes me the
amount of misinformation spread on this subject. This thread started with
gross misinformation and is continuing in a like manner.
Mark Kovalsky
SVO23turbo wrote:
>You are describing flywheel hp and adding frictional hp to it as gross hp.
> I've never seen this mentioned anywhere. On top of that it has very little use
> since the frictional loses of an engine can vary widely. Why on Earth would
> someone choose to use such an ambiguous system? I doubt they would hence the
> whole reason gross hp was dropped. You could no doubt measure the frictional
> hp it takes to spin an engine a certain rpm, but its meaningless in
> relationship to that engines output. Output is all that is cared about. Gross
> hp is hp output with few specific concerns. Think of it as an engines ideal
> output. Net hp is the output the engine makes with the accessories in place,
> the exhaust in place, and the induction system in place as mounted in the car
> including the air silencer and things of this nature. Please go read the SAE
> handbook or some automotive books at your local bookstore.
I sit corrected.
I got out my SAE handbook and read SAE J1349, Engine Power Test Code
Spark Ignition and Diesel.
I was thinking about Indicated horsepower. That is net plus frictional.
Gross horsepower is an engine without aircleaner, fan, etc.
SVO23turbo
>I sit corrected.
>
>I got out my SAE handbook and read SAE J1349, Engine Power Test Code
>Spark Ignition and Diesel.
>
>I was thinking about Indicated horsepower. That is net plus frictional.
>
>Gross horsepower is an engine without aircleaner, fan, etc.
Thanks. I really just wanted to clear up the confusion on this rather
laborious topic of late. I wish I had that book handy such as yourself. I
haven't had access to one since college, but I remember making good use of it
while there.