Hi all,

This group often sees questions about ratings (can my 2 hp electric
motor develop 3 hp? can I draw 150 A from my 100 A supply? etc.) so I'd
like to ask a rating question. I think this one might spark some debate.
If you buy a good electric motor, the power rating is a continuous one
(or it says otherwise). Same with most pieces of industrial equipment.
But what about a car? Is the 130 hp or whatever maximum engine power the
manufacturer quotes a continuous or an intermittent rating? I was always
under the impression that it was an intermittent rating, though quite
where I got that idea I can't remember. I'm not asking if the engine
will wear out quickly developing its maximum power rating continuously -
I'm sure it will - I'm just wondering if it will overheat?

Any thoughts? Just a matter of curiousity...

Best wishes,

Chris

"Christopher Tidy" wrote in message
...
Hi all,

This group often sees questions about ratings (can my 2 hp electric
motor develop 3 hp? can I draw 150 A from my 100 A supply? etc.) so
I'd
like to ask a rating question. I think this one might spark some
debate.
If you buy a good electric motor, the power rating is a continuous one
(or it says otherwise). Same with most pieces of industrial equipment.
But what about a car? Is the 130 hp or whatever maximum engine power
the
manufacturer quotes a continuous or an intermittent rating? I was
always
under the impression that it was an intermittent rating, though quite
where I got that idea I can't remember. I'm not asking if the engine
will wear out quickly developing its maximum power rating
continuously -
I'm sure it will - I'm just wondering if it will overheat?

Any thoughts? Just a matter of curiousity...

Best wishes,

Chris


HP is not directly measured in either case. It is based on an equation
using the torque and RPM. In a normal auto engine the torque and HP both
have a peak number. That is the number most often quoted. If the cooling
system is properly designed for the engine it will not overheat BUT it
will run warmer than it normally would. However most AUTO engines built
cannot handle running at the max numbers for long because they are made
so light to save fuel.



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In article ,
"Steve W." wrote:



HP is not directly measured in either case. It is based on an equation
using the torque and RPM. In a normal auto engine the torque and HP both
have a peak number. That is the number most often quoted. If the cooling
system is properly designed for the engine it will not overheat BUT it
will run warmer than it normally would. However most AUTO engines built
cannot handle running at the max numbers for long because they are made
so light to save fuel.


The rule of thumb we used for sizing brakes for overhead crane motors
was:

5250 X RPM / HP = torque

Should be able to get the HP as the unknown with a little algebra.






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"John Husvar" wrote in message
...
In article ,
"Steve W." wrote:



HP is not directly measured in either case. It is based on an equation
using the torque and RPM. In a normal auto engine the torque and HP both
have a peak number. That is the number most often quoted. If the cooling
system is properly designed for the engine it will not overheat BUT it
will run warmer than it normally would. However most AUTO engines built
cannot handle running at the max numbers for long because they are made
so light to save fuel.


The rule of thumb we used for sizing brakes for overhead crane motors
was:

5250 X RPM / HP = torque

Should be able to get the HP as the unknown with a little algebra.



Hi John

The equation in your post has been published with a significant error. I
am sure it is a "typo". HP equals Torque times RPM.
Yeah, the automotive design guys *do* measure the HP of the engines they
develop.

It is kinda interesting that at about 5,250 RPM the Torque *and* the HP
are the same number when measured with the commonly used USA dimensions.
So, an engine producing 200 HP at 5,250 RPM will be producing 200 ft lbs
of Torque.

Jerry

"Jerry Martes" wrote in message
news:GffSf.12418$%e1.4667@trnddc05...

"John Husvar" wrote in message
...
In article ,
"Steve W." wrote:



HP is not directly measured in either case. It is based on an
equation
using the torque and RPM. In a normal auto engine the torque and HP
both
have a peak number. That is the number most often quoted. If the
cooling
system is properly designed for the engine it will not overheat BUT
it
will run warmer than it normally would. However most AUTO engines
built
cannot handle running at the max numbers for long because they are
made
so light to save fuel.


The rule of thumb we used for sizing brakes for overhead crane
motors
was:

5250 X RPM / HP = torque

Should be able to get the HP as the unknown with a little algebra.



Hi John

The equation in your post has been published with a significant
error. I
am sure it is a "typo". HP equals Torque times RPM.
Yeah, the automotive design guys *do* measure the HP of the engines
they
develop.

It is kinda interesting that at about 5,250 RPM the Torque *and* the
HP
are the same number when measured with the commonly used USA
dimensions.
So, an engine producing 200 HP at 5,250 RPM will be producing 200 ft
lbs
of Torque.

Jerry


HP = Torque (lbft) X RPM / 5252



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The fundamental formula for horsepower sez:

HP = [ (WRN x 2 pi) / 33000 ] Visualize a rope on a windlass arrangement
wound around a shaft of radius "R"; the rope is supporting a load of "W",
and the shaft is turned at a number of revolutions, "RPM"

Whe R = Radius or length of a lever arm about the center of a shaft, in
feet
W = force, weight, in pounds
N = Number of revolutions, RPM

Supposedly, this is the original formula, traceable to James Watt.
Simplifying the formula by dividing out the 2 pi term yields: HP = [ WRN /
5252 ] WR is torque, thus the familiar form becomes: HP = [ (Torque x RPM)
/ 5252 ] or Torque = [ (HP x 5252) / RPM ]

Bob Swinney

"Christopher Tidy" wrote in message
...
Hi all,

This group often sees questions about ratings (can my 2 hp electric motor
develop 3 hp? can I draw 150 A from my 100 A supply? etc.) so I'd like to
ask a rating question. I think this one might spark some debate. If you
buy a good electric motor, the power rating is a continuous one (or it
says otherwise). Same with most pieces of industrial equipment. But what
about a car? Is the 130 hp or whatever maximum engine power the
manufacturer quotes a continuous or an intermittent rating? I was always
under the impression that it was an intermittent rating, though quite
where I got that idea I can't remember. I'm not asking if the engine will
wear out quickly developing its maximum power rating continuously - I'm
sure it will - I'm just wondering if it will overheat?

Any thoughts? Just a matter of curiousity...

Best wishes,

Chris


I would think that hooking it up to a Nextel Cup radiator would keep it from
overheating. Then again, racing engines have things like sodium filled
valve stems and such to manage the localized heat around the combustion
chamber so maybe not.

Steve.

Back in the muschle car days, they would do everything they could to
come up with a max Hp rating to advertise. IIRC, one major mfr took
all the accessories off the engine (water pumps, generator, etc. and
even used a vacuum system to extract waste gases to get a MAX number to
put in the ads.
I remember hearing that a mfr of industrial equipment ordered 60 hp
engines from both Caterpillar and from Ford to test for some continuous
duty application. The ford engine failed miserably when asked to
deliver 60 hp continuosly, even though it was rated for it. I have a
Ford engine in my backhoe. It has 3 different HP ratings, all the way
from 62 HP down to 42 HP depending on whether its pumping its own water,
etc., I consider it a 42 HP engine and it behaves that way.


Pete Stanaitis
-------------------------

Christopher Tidy wrote:

Hi all,

This group often sees questions about ratings (can my 2 hp electric
motor develop 3 hp? can I draw 150 A from my 100 A supply? etc.) so I'd
like to ask a rating question. I think this one might spark some debate.
If you buy a good electric motor, the power rating is a continuous one
(or it says otherwise). Same with most pieces of industrial equipment.
But what about a car? Is the 130 hp or whatever maximum engine power the
manufacturer quotes a continuous or an intermittent rating? I was always
under the impression that it was an intermittent rating, though quite
where I got that idea I can't remember. I'm not asking if the engine
will wear out quickly developing its maximum power rating continuously -
I'm sure it will - I'm just wondering if it will overheat?

Any thoughts? Just a matter of curiousity...

Best wishes,

Chris

spaco wrote:

Back in the muschle car days, they would do everything they could to
come up with a max Hp rating to advertise. IIRC, one major mfr took
all the accessories off the engine (water pumps, generator, etc. and
even used a vacuum system to extract waste gases to get a MAX number
to put in the ads.

They ALL do this! Latest procedure is to run the camshaft with a big
induction
motor on a flux vector drive, so it is in sync with the crank, but not
drawing any
power from the crankshaft. This runs the oil pump off external power,
too, on
most engines.


Jon

Jon Elson wrote:



spaco wrote:

Back in the muschle car days, they would do everything they could to
come up with a max Hp rating to advertise. IIRC, one major mfr took
all the accessories off the engine (water pumps, generator, etc. and
even used a vacuum system to extract waste gases to get a MAX number
to put in the ads.

They ALL do this! Latest procedure is to run the camshaft with a big
induction
motor on a flux vector drive, so it is in sync with the crank, but not
drawing any
power from the crankshaft. This runs the oil pump off external power,
too, on
most engines.

Uh huh. The SAE standards were revised to eliminate such practices
something like 20 years ago.

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

"J. Clarke" wrote:

Jon Elson wrote:



spaco wrote:

Back in the muschle car days, they would do everything they could to
come up with a max Hp rating to advertise. IIRC, one major mfr took
all the accessories off the engine (water pumps, generator, etc. and
even used a vacuum system to extract waste gases to get a MAX number
to put in the ads.

They ALL do this! Latest procedure is to run the camshaft with a big
induction
motor on a flux vector drive, so it is in sync with the crank, but not
drawing any
power from the crankshaft. This runs the oil pump off external power,
too, on
most engines.

Uh huh. The SAE standards were revised to eliminate such practices
something like 20 years ago.

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

They also raise the temperature from 60 degrees to 77 degrees to which
you correct HP and torque. At the same time dropping Barometric Pressure
from 29.92 to 29.23. In other words lower HP ratings from the same
engine. Old SAE J816 new SAE J1349.
Stan
Stan

On Thu, 16 Mar 2006 12:17:57 -0600, spaco
wrote:

Back in the muschle car days, they would do everything they could to
come up with a max Hp rating to advertise. IIRC, one major mfr took
all the accessories off the engine

This is standard practice in the USA. SAE ratings exclude auxilliary
drives, Euro ratings include them.

Just one reason why '70s US cars had huge engines with gazillion
horsepower ratings, but European cars were often faster in reality.

Corners were the other reason.

On Thu, 16 Mar 2006 03:13:05 +0000 (UTC), Christopher Tidy
wrote:

But what about a car? Is the 130 hp or whatever maximum engine power the
manufacturer quotes a continuous or an intermittent rating?

Continuous, but at a constant rpm which is unrealistic for anything
except motorway cruising. It's done by measuring on a dyno, either an
engine dyno or a rolling road.

It's usually quoted at some ridiculous rpm limit too, fairly close to
the redline. Long stroke engines with small valves will have failry
flat curves (i.e. torque is approximately constant with speed), highly
tuned engines (motorbikes) have "peaky" torque curves, so max power only
happens when you rev hard.

On Fri, 17 Mar 2006 23:31:11 +0000, Andy Dingley
wrote:

On Thu, 16 Mar 2006 03:13:05 +0000 (UTC), Christopher Tidy
wrote:

But what about a car? Is the 130 hp or whatever maximum engine power the
manufacturer quotes a continuous or an intermittent rating?

Continuous, but at a constant rpm which is unrealistic for anything
except motorway cruising. It's done by measuring on a dyno, either an
engine dyno or a rolling road.

It's usually quoted at some ridiculous rpm limit too, fairly close to
the redline. Long stroke engines with small valves will have failry
flat curves (i.e. torque is approximately constant with speed), highly
tuned engines (motorbikes) have "peaky" torque curves, so max power only
happens when you rev hard.

But most cars are driven with insufficient use of the gearbox. Whereas on a
bike the gearbox is a natural extension of the driving style. So the engine
types work for their intended uses.


Mark Rand
RTFM

On Sat, 18 Mar 2006 01:32:13 +0000, with neither quill nor qualm, Mark
Rand quickly quoth:

But most cars are driven with insufficient use of the gearbox. Whereas on a
bike the gearbox is a natural extension of the driving style. So the engine
types work for their intended uses.

Y'mean like Grandpappy, who's already in 4th gear by 25 kph?

--
"I'm sick and tired of having to rearrange my life
because of what the STUPIDEST people *might* do or
how they *might* react."
-- Bill Maher

On Sat, 18 Mar 2006 01:32:13 +0000, Mark Rand
wrote:

On Fri, 17 Mar 2006 23:31:11 +0000, Andy Dingley
wrote:

On Thu, 16 Mar 2006 03:13:05 +0000 (UTC), Christopher Tidy
wrote:

But what about a car? Is the 130 hp or whatever maximum engine power the
manufacturer quotes a continuous or an intermittent rating?

Continuous, but at a constant rpm which is unrealistic for anything
except motorway cruising. It's done by measuring on a dyno, either an
engine dyno or a rolling road.

It's usually quoted at some ridiculous rpm limit too, fairly close to
the redline. Long stroke engines with small valves will have failry
flat curves (i.e. torque is approximately constant with speed), highly
tuned engines (motorbikes) have "peaky" torque curves, so max power only
happens when you rev hard.

But most cars are driven with insufficient use of the gearbox. Whereas on a
bike the gearbox is a natural extension of the driving style. So the engine
types work for their intended uses.

Particularly when most American iron today turns less than 2000 RPM at
the legal speed limit in top gear. Where it's producing something like
75 HP at full load, or more likely closer to 35 or 40HP at cruise.

The engines, in most cases, ARE capable op putting out 80% power for
hours on end at the rated RPM though - which IS rather incredible. A
smallblock 8 cranking 6000 RPM for several hours at a time - with
virtually the same geometry a sicties or seventies engine had trouble
staying together at 4000 for a few minutes, or 6000 for 1/4 mile.


Mark Rand
RTFM

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Andy Dingley wrote:
On Thu, 16 Mar 2006 03:13:05 +0000 (UTC), Christopher Tidy
wrote:


But what about a car? Is the 130 hp or whatever maximum engine power the
manufacturer quotes a continuous or an intermittent rating?


Continuous, but at a constant rpm which is unrealistic for anything
except motorway cruising. It's done by measuring on a dyno, either an
engine dyno or a rolling road.

Thanks for some interesting opinions. It looks like most people think
the rating is intermittent (big for the purposes of advertising), but a
few think it is continuous. I had a thought last night which perhaps
sheds some light on it. Car manufacturers are cheap, and not all car
buyers are as mechanically minded as us. They'll build the lightest,
cheapest engine that'll do the job, then figure out a way to bump up the
horsepower rating. Makes sense!

Chris

On Sat, 18 Mar 2006 02:48:30 +0000 (UTC), Christopher Tidy
wrote:

Andy Dingley wrote:
On Thu, 16 Mar 2006 03:13:05 +0000 (UTC), Christopher Tidy
wrote:


But what about a car? Is the 130 hp or whatever maximum engine power the
manufacturer quotes a continuous or an intermittent rating?


Continuous, but at a constant rpm which is unrealistic for anything
except motorway cruising. It's done by measuring on a dyno, either an
engine dyno or a rolling road.

Thanks for some interesting opinions. It looks like most people think
the rating is intermittent (big for the purposes of advertising), but a
few think it is continuous. I had a thought last night which perhaps
sheds some light on it. Car manufacturers are cheap, and not all car
buyers are as mechanically minded as us. They'll build the lightest,
cheapest engine that'll do the job, then figure out a way to bump up the
horsepower rating. Makes sense!

Chris

OK, maybe we're mechanically minded, but I'll bet you can't find car
owners cheaper than this bunch. From reading the posts, I'd guess the
average transportation for this group has about 150-300,000 mi. and is
old enough for vintage tags.

Pete Keillor

On Sat, 18 Mar 2006 06:54:10 -0500, Pete Keillor
wrote:



OK, maybe we're mechanically minded, but I'll bet you can't find car
owners cheaper than this bunch. From reading the posts, I'd guess the
average transportation for this group has about 150-300,000 mi. and is
old enough for vintage tags.

Pete Keillor


Gasoline? We don't want no skinkin' gasoline... It falls right off the shovel
and runs right through the bars of the grate. BG


Mark Rand
RTFM

Pete Keillor wrote:

On Sat, 18 Mar 2006 02:48:30 +0000 (UTC), Christopher Tidy
wrote:



Andy Dingley wrote:


On Thu, 16 Mar 2006 03:13:05 +0000 (UTC), Christopher Tidy
wrote:




But what about a car? Is the 130 hp or whatever maximum engine power the
manufacturer quotes a continuous or an intermittent rating?


Continuous, but at a constant rpm which is unrealistic for anything
except motorway cruising. It's done by measuring on a dyno, either an
engine dyno or a rolling road.


Thanks for some interesting opinions. It looks like most people think
the rating is intermittent (big for the purposes of advertising), but a
few think it is continuous. I had a thought last night which perhaps
sheds some light on it. Car manufacturers are cheap, and not all car
buyers are as mechanically minded as us. They'll build the lightest,
cheapest engine that'll do the job, then figure out a way to bump up the
horsepower rating. Makes sense!

Chris



OK, maybe we're mechanically minded, but I'll bet you can't find car
owners cheaper than this bunch. From reading the posts, I'd guess the
average transportation for this group has about 150-300,000 mi. and is
old enough for vintage tags.

Pete Keillor



My Toyota only has 140,000 on it. Almost broken in! grin

Fred

Christopher Tidy wrote:

Hi all,

This group often sees questions about ratings (can my 2 hp electric
motor develop 3 hp? can I draw 150 A from my 100 A supply? etc.) so I'd
like to ask a rating question. I think this one might spark some debate.
If you buy a good electric motor, the power rating is a continuous one
(or it says otherwise). Same with most pieces of industrial equipment.
But what about a car? Is the 130 hp or whatever maximum engine power the
manufacturer quotes a continuous or an intermittent rating? I was always
under the impression that it was an intermittent rating, though quite
where I got that idea I can't remember. I'm not asking if the engine
will wear out quickly developing its maximum power rating continuously -
I'm sure it will - I'm just wondering if it will overheat?

If it is a typical liquid cooled engine then whether it will overheat or not
depends on components external to the engine, so as posed it's an
unanswerable question.

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)