more stupid questions!


Adam
03-14-2001, 03:08 PM
What does the "b" in bhp stand for? what is the difference between torque & horsepower? I have heard detailed descriptions of horsepower but not torque....

GOD
03-14-2001, 03:11 PM
base horse power .......does that answer ur question :rolleyes:

Adam
03-14-2001, 03:36 PM
1 of em:D

CraigFL
03-14-2001, 04:41 PM
actually the "B" stands for "Brake" because dynomometers used brakes(of some type) to resist the motor torque which is used with RPM to calculate HP

enzo@af
03-14-2001, 07:07 PM
Yes, it's "brake".

Torque is a rotational force. Kind of a strange concept, but I usually think of it like this....if you twist off a bottle cap, you apply torque. If you lift something, or pull something (straight line force) you are using power (hp).

Torque in a car can be found by this equation.....
(hp * 5200)/RPM

I think that's it...don't remember exactly.

JD@af
03-18-2001, 07:59 PM
You're almost right: its 5252. In layman's terms, horsepower is simply an application of torque. There are in general two ways to make big horsepower: large amounts of torque at moderate rpm, or moderate amounts of torque at high rpm.

A better measure of an engine's capabilities than horsepower is its torque, and in fact its torque curve. From that you can easily extrapolate the horsepower curve, as the horsepower curve is similar to a derivative (an old term from calculus - which by the way I passed by the skin of my teeth - but it follows the same principle).

Hopefully this example will help explain the horsepower versus torque principle. Texan posted a good explanation of this on SHO. I've got it on my computer at work, so I'll repost it here later.

Psman32@af
03-21-2001, 04:23 PM
hey enzo, you got that off of Popular Hot Rodding didn't you? I watch the same thing every chance I get. Thats what they said a few weeks ago.

JD@af
03-21-2001, 05:33 PM
damn, I swear I have typed this explanation out like four times but never have saved it . OK, so here's the speech again in layman's terms, hope it covers everything (and accurately)...

HP= a measure of forced over time, where 1 hp is equal to 550 lbs lifted one foot in one second. Expressed in terms of torque, 1 hp equals 550 ft/lbs per second. Noticed this measurement is time based.

Torque= the measure of instantaneous rotational force an engine can produce. Notice this measurement is not time based.

hp= torque x RPM / 5252
torque= hp x 5252/ RPM


With these two basic equations, you can figure out how much hp or torque you have at a given RPM with either measurement. Notice that because of this equation, an engine can NEVER make as much hp before 5252 RPM as it can torque, and the opposite is true above 5252 RPM. Any dyno chart you ever see where the two plotted curves don't cross at 5252 RPM is a bogus dyno chart.

What's important to understand as this pertains to vehicles is that hp is not a direct determinate to accelerative ability. Horsepower is more a way of easily summarizing the abilities of a car, but not an exact or necessary thing. Horsepower is basically a way of stating torque with gearing already taken into account, which makes the pain of figuring out torque multiplication factors less needed for generalized performance figures. Here's the three most important factors in determining how fast a car can accelerate...

-effective torque at the wheels
-overall vehicle weight
-available traction
-total drag (constituted mainly of aero drag at speeds above 50mph)

Since we are just talking about differences in power and how it effects acceleration, we can basically toss out everything except torque since the others can be assumed to remain constant(please remember this is just a simple hypothetical). So now you need to understand what torque multiplication is, and here's an excerpt from an older post I made on the subject...

"What this all means comes into focus when you understand the concept of torque multiplication.
Torque is the only productive force that an engine creates, so when talking about acceleration
relative to gearing this is all that matters. Torque multiplication takes the torque output of the
engine at any specific RPM and multiplies it by the overall gear ratio (think of this as gear
reduction) to show us how much torque is actually being transmitted to the wheels at any given
speed and in any given gear. An example:

Engine A is making 150 ft/lbs of torque at 3000 RPM, and is in our earlier hypothetical 1st gear
which has a ratio of 3.42:1 and a final drive of 4.27:1.

Effective torque at the wheels @ 3000RPM = 4.27 x 3.42 x 150...
which equals 2,190 ft/lbs of torque to the wheels! Ever wonder why acceleration is always better
in lower gears than higher gears? That's why. The true accelerative ability of a car is defined by
these laws, and in the most pure sense torque at the wheels is all that matters (meaning HP is
not directly important or a determinate of potential speed). "


So knowing all this new stuff, you should be starting to see the big picture. Now you have the
definitions of horsepower, torque and torque multiplication, along with a basic understanding of
what they mean. All the concepts surrounding this haven't been covered here, so if anything isn't
clear or I forgot something important please just say so, and either I or someone else can fill in
the blanks. Hope this helps, peace

Psman32@af
04-06-2001, 10:28 PM
Hey JD, thanx for the repost of that, I learned alot and have since developed a formula to calculate 0-60 mph time that will be within 5% of the true numbers.
I noticed something about those gears. The torque seems to be kinda on the small side so taking the tire size of a tempo (215/70R/14) with a redline of 6000 rpm, that gear will only last to 29.6 mph, and that is being a little generous.
And also to the texan, torque is directly related to acceleration but horsepower gets you the top speed.

Chris
04-24-2001, 05:57 PM
This is some good info, bu tI knew it all already. It took awhile, though. Could you post that 0-60mph formula? Please?
Also, you can calculate horsepower from the quarter mile time. It can be off by a fair bit (usually less than the car has) but it is a rough approkamentation.
hp=(mph\234)to the exponent 3, *vehicle weight.
Examle, it goes 125 mph in the quarter.
135/234=.534
.534*.534*.534=.15
.15*3000=457 bhp

Try it with other vehicles. If it is driven really well, it should be close. But some cars (like big SUV's) can be up to 20% off.
Still, a general rule is better than none:)

texan
04-25-2001, 03:59 AM
Psman32@af- Actually, I have never understood why people think hp is what determines top speed. Now I'm not saying it's not, but I would like you to answer this hypothetical on top speed....

A vehicle has an engine producing a perfectly constant torque output. For this example, we'll say 200 lbs/ft at all RPM, with a redline of 10,000 RPM. So it's now easy to calculate hp from this, but what about top speed based upon that hp output?

Let's say this vehicle's top gear allows it to put down 640 lbs/ft of effective torque to the wheels (a 0.8:1 gear with a 4:1 final drive) throughout all of said top gear. Now we'll say this motor at redline, in this gear, can reach 200 mph. Now at 150 mph the total resistance to motion is 640 lbs/ft of pressure, while 200 mph is 700 lbs/ft of pressure. So since the horsepower curve is still climbing (to a total of 380hp @ 10,000 RPM), would the vehicle continue to accelerate or reach top speed at 150 mph?

sracing
12-09-2004, 08:09 AM
Psman32@af- Actually, I have never understood why people think hp is what determines top speed. Now I'm not saying it's not, but I would like you to answer this hypothetical on top speed....

A vehicle has an engine producing a perfectly constant torque output. For this example, we'll say 200 lbs/ft at all RPM, with a redline of 10,000 RPM. So it's now easy to calculate hp from this, but what about top speed based upon that hp output?

Let's say this vehicle's top gear allows it to put down 640 lbs/ft of effective torque to the wheels (a 0.8:1 gear with a 4:1 final drive) throughout all of said top gear. Now we'll say this motor at redline, in this gear, can reach 200 mph. Now at 150 mph the total resistance to motion is 640 lbs/ft of pressure, while 200 mph is 700 lbs/ft of pressure. So since the horsepower curve is still climbing (to a total of 380hp @ 10,000 RPM), would the vehicle continue to accelerate or reach top speed at 150 mph?


All other things being equal hp DOES determine top speed.
IE. If the cars are drag equivelant (rolling and aero) the car with the greatest HP can go the fastest. (assuming final gearing is correct) Both cars will accelerate until all possible work energy is used. Please note that drag is not linear. eg. To double your speed takes 4 times the energy.

Jim
SR Racing

curtis73
12-09-2004, 11:16 AM
All other things being equal hp DOES determine top speed.
IE. If the cars are drag equivelant (rolling and aero) the car with the greatest HP can go the fastest. (assuming final gearing is correct) Both cars will accelerate until all possible work energy is used. Please note that drag is not linear. eg. To double your speed takes 4 times the energy.

Jim
SR Racing

True, but the only reason the one car has more hp is because it either has more torque, or the torque comes later in the RPM band. It either makes more overall torque, or the torque it does make has more inertia behind it... which is basically what hp is; torque over a period of time.

HP comes from torque, so in order to get more HP, you have to either have more torque, or make the torque peak higher in the RPMs so that it generates more HP. Without torque in a rotational engine, there is no such thing as HP.

sracing
12-09-2004, 11:51 AM
True, but the only reason the one car has more hp is because it either has more torque, or the torque comes later in the RPM band. It either makes more overall torque, or the torque it does make has more inertia behind it... which is basically what hp is; torque over a period of time.

HP comes from torque, so in order to get more HP, you have to either have more torque, or make the torque peak higher in the RPMs so that it generates more HP. Without torque in a rotational engine, there is no such thing as HP.

That is correct. Except... "or the torque it does make has more inertia behind it".? There are no free lunches in thermodynamics. Torque is Torque (or force is force). Inertia is simply stored energy (HP) that came from the engine at some point in time.

BTW, a quiz. Ever seen an engine that produces maximum torque at zero RPM?

Jim
SR Racing

curtis73
12-09-2004, 12:02 PM
Yeah a steam engine. Good question. I love those old steamies. My dad and I used to go the Grainger's Picnics when I was a kid. Growing up in Amish country, there were so many of those old steam tractors. *sniff* I can smell the coal burning now. :)

You're right... "inertia" was a bad word to use. I tried to use it as a metaphor for demonstration's sake, but it didn't come across.

sracing
12-09-2004, 12:34 PM
Good on the steam engine. It fools most people.

I see the point you were trying to make with "inertia". As a matter of fact, it is one way brake dyno operators fool the customer re: hp of an engine. If I make the run downward in RPM when applying the load I can use that extra stored "inertia" to pick up a few extra lbs of torque (ie HP) at the RPM range I want.

Jim
SR Racing

buymeabmwm3
12-13-2004, 01:41 PM
An electric motor produces max torque at zero RPM. If i remember correctly, it actually produces infinite torque at zero RPM.

psychorallyfreak
12-13-2004, 01:45 PM
I think you may have missed the point...
Creating maximum torque at zero RPM, because it has no balls.

buymeabmwm3
12-13-2004, 01:49 PM
What?

sracing
12-13-2004, 05:23 PM
An electric motor produces max torque at zero RPM. If i remember correctly, it actually produces infinite torque at zero RPM.

Infinite? Nope. I can hold a 1/4 HP motor back by hand from 0 RPM.

Jim
SR Racing

CBFryman
12-13-2004, 06:51 PM
Well just to let you all know. HP is totaly reliant on torque.
Torque is Work. Horsepower is work done over time with speed. HP is a fine way to measure an engines performance. only thing is you also have to look at what RPM that HP is at. sure an S2000 makes 240hp but its at well over normal operating range.
people always say "has good botom end torqe, so it gets off the line quicker" well this is true. if you launch 2 cars from the same RPM. but if you make peak power at 6000RPM then you should launch from there. because This is where you are going to do the most work the quickest. so this is where you are going to accelerate the quickest. good low end torque is great for everyday driving because this means you have more low end HP. but as far as for pure pwerformance a smaller amount of torque doing its work quicker is more valuable.
also, all of the formulas above are for 33,000 lb/ft seconds and Lb/Ft. other ways to rate "Horse Power" often used in europe is in KiloWatts. 1 Hp=746w. and N/M (neuton meters) and Kilogram/Meters is used in countries other than america.
Damn our standard system.
as for the BHP. BHP stands for Brake Horse Power as has been said. this measures horsepower and torque to the flywheel. it uses a brake to put anti rotation force (counter torque) on the flywheel to simulate a load. these are more acurate compared to a cyntrifical or jet dyno but they only rate to the flywheel. what matters is what yo uget to the wheels.
a Cuntrifical dyno measures how quickly an engine can accelerate a very heavy cylender. a Jet duno uses a stream of fluid to create counter torque. both will give a very close figure but if you dyno a car once and then dyno it 5 seconds later on the same dyno it may be a few HP points off and it can be as much as 20hp off between dyno's. Jet Dynos are largely used to measure WHP but cyntrifical dynos are also used.

sracing
12-13-2004, 07:44 PM
Well just to let you all know. HP is totaly reliant on torque. Torque is Work.

Nope. Torque is Force only. Usually used in reference to rotational force. It is NOT work.

..also, all of the formulas above are for 33,000 lb/ft seconds and Lb/Ft. other ways to rate "Horse Power" often used in europe is in KiloWatts. 1 Hp=746w. and N/M (neuton meters) and Kilogram/Meters is used in countries other than america.

Nope. HP can be converted to Watts, BTU or Calories / sec, but they all come out to the same when converted. Some countries do use watts interchangably. I think what you thinking of is other countries use of different correction factors. DIN, vs. SAE, STP, etc.

BHP stands for Brake Horse Power as has been said. this measures horsepower and torque to the flywheel.

Often true. But it really refers to the meaurement via measuring torqe(force) with a brake. It can be rear wheel brake horsepower just as easily and flywheel brake horsepower.

it uses a brake to put anti rotation force (counter torque) on the flywheel to simulate a load. these are more acurate compared to a cyntrifical or jet dyno but they only rate to the flywheel.

Nope again. :evillol:

Actually a brake dyno is usually a bit LESS accurate than an inertia dyno. (What you are calling a jet dyno is probably a Dynojet dyno. This is a brand name. Which can be either a brake or inertia dyno.)
A brake dyno is a bit less accurate in most cases due to it being used to run an engine up and/or down it's RPM range. This is prone to operator error and will measure differently depending upon the rate that the engine is accelerated at as engine component inertia will cause errors.
An Inertia Dyno is all other things equal the most reliable for the actual HP as far as repeatabity etc. It simply measures the amount of time it takes to accelerate a known mass. Usually drums or rolls that equate to about 2000-2500 lbs of rolling mass. This makes calculations very precise with little chance for operator error.

a Cuntrifical dyno measures how quickly an engine can accelerate a very heavy cylender.

Actually it's called an inertial dyno.

..a Jet duno uses a stream of fluid to create counter torque.

Actually it uses a hydraulic brake or eddy current brake to simply hold the engine back. The hydraulic type is usually an impeller in a seal container called the load cell. The Edddy current type is sort of an electric brake.

The brake dyno measures Torque and RPM and computes the HP based upon that. (The Torque is measured with a Strain Gauge or Pressure Transducer of some type. This tranducer is also one reason why it is sometimes not as accurate. They are sensitive to environmental conditions and noise.)

The Inertia dyno simply measures the time it take to accelerate the drum. An accurate timer is all that is needed. It has no other dependencies other than RPM measurement.

..it may be a few HP points off and it can be as much as 20hp off between dyno's.

Then one dyno is simply WRONG and/or the correction factors are wrong and/or the engine is broke. (heat swamp, etc.)

Jet Dynos are largely used to measure WHP but cyntrifical dynos are also used.

Brake Dyno and Inertia Dyno, not "Jet Dyno and cyntrifical" dynos.

BTW, Good dyno shops use wheel dynos that have both Brake (Eddy Current) and Inertia Dynos integrated. It is the ONLY way to accurately test and tune a vehicle.

Jim
SR Racing
(Owners of Chassis Dyno's Eddy Current and Inertia and Engine Dyno's, and lots of other neat toys.)




Jim
SR Racing

bjdm151
12-14-2004, 08:53 AM
Jim,

Stop playing so rough,

The word of Jim Schings is law........almost always......... but especially when he signs my pay check!!!!!!

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