Explain: KiloWatt & Break Horse Power

[michael_is]

I'm going to put myself on the line by asking a question to which most motor emphesus seem to know.

How strong is a KiloWatt (kW)?
How strong is a Break Horse Power?
Is there anyway to approx. the power output without running a dyno?
How doyou relate the kW/HP output in terms of the car out on the road - The acceleration? The top speed?

- Alright. so some of these questions may sound weak but I'm having trouble finding answers.
There's defintly other questions i need answering but I can't think of any at the present time.

I hear people talking about their cars and how much kW/HP it "puts out" but it's hard to compare it to anything.
Even when I started googling, alot of the answers I was finding were contradicting each other.

Please don't hurt me :p

[Magnus]

Regarding if it is possible to calculate you can look here:
http://www.dragtimes.com/horsepower-et-trap-speed-calculator.php
(Which is hp=mass/(ET/5.825)^3) and/or hp=mass*(speed/234)^3)
The very unscientific power on one hp is the ability to lift 75 kgs one meter in one second.
One kilowatt is 1,36 hp.
There are a lot of different standards, the most important being DIN and SAE (something like Deutche Industrie Norme and Society of Automotive Engineers). DIN is a tougher measure which tells the engines output with all equipment (AC, Generaror, fans, exhaust etc) while the SAE tells the engines grossoutput without any energyconsuming equipment. Thus, the DIN figure is always lower then the SAE.

[Mark]

Kilowatt and horsepower are two measurements of the same thing namely power and power is work done per unit time usually per second so they are a measure of how much work is done by the engine. The figures are hard to relate to real life as the speed and acceleration depends on many other factors such as weight / transmission efficiency etc So you can't just say a car with x horsepower will do x miles per hour.

[Kneeslider]

As Mark says, Kilowatts and Brake horsepower are both measurements of the same thing. When trying to measure 'how good' an engine is, we need to find out how much energy it is capable of producing. Physicists and engineers call this sort of energy mechanical, or kinetic energy. If you look up Kinetic energy, you will find that it is defined by the following equation:-

Ke = 1/2 mv²

Where Ke is the quantity of kinetic Energy measured in joules
M is the mass in Kg
V is the velocity in meters per second, then squared (multiplied by itself)

One Watt, is one joule per second ( or Ke/time in seconds) so one Kilowatt is one thousand joules per second.

One horsepower = 745.69 watts

[Valve Bounce]

I am looking forward to how you can measure HP without a dyno; I am sure some of our top end nerds here have already figured out some way by pointing a mouse from a laptop at a passing F1 car down the straight.

Acceleration is dependent on torque and not HP. Again, I await some of the younger boffins here to explain all this in detail.

It is very interesting that, in comparison, how current cars prform against sports cars of old. I think the XK150's zero to 60 MPH time was 7.3 seconds while the corvette of the same era did it in 7.0. Nowadays, many family sedans would make that look like small potatoes.

Still, I wish to hell I could have a white convertible XK150. I have written to Santa all these years, but I must have been bad during the year. :(

[Magnus]

I am looking forward to how you can measure HP without a dyno; I am sure some of our top end nerds here have already figured out some way by pointing a mouse from a laptop at a passing F1 car down the straight.

Acceleration is dependent on torque and not HP. Again, I await some of the younger boffins here to explain all this in detail.
:(
I am not quite shure if you are joking or not, but to calculate energy development on the basis of a few variables is very simple math. Of course using a dyno is much more precise, but most boy racers cannot afford a dyno, so instead they calculate a little bit or buy a accelerometer(from abt 150-200euro).

And naturally you can make rough estimates of the power on an F1 car aswell if you have start speed, end speed, weight, Cw etc.

Regarding acceleration it is depending on a whole lot of stuff, most of all the design of your camshaft, lobe, flanks and so on which comes down to in what rpm-region you want your car to have its best acceleration.

And yes: torque is the force with which you can apply to your wheels. Power is how often you can do it.

[airshifter]

I'm going to put myself on the line by asking a question to which most motor emphesus seem to know.

How strong is a KiloWatt (kW)?
How strong is a Break Horse Power?
Is there anyway to approx. the power output without running a dyno?
How doyou relate the kW/HP output in terms of the car out on the road - The acceleration? The top speed?

- Alright. so some of these questions may sound weak but I'm having trouble finding answers.
There's defintly other questions i need answering but I can't think of any at the present time.

I hear people talking about their cars and how much kW/HP it "puts out" but it's hard to compare it to anything.
Even when I started googling, alot of the answers I was finding were contradicting each other.

Please don't hurt me :p

Here's a good link that relates the two measurements of power very well. It might surprise you who came up with the term horsepower, and how closely it is related to watts. :D

http://www.howstuffworks.com/horsepower.htm


In terms of accurate measurement, a dyno is the best way to calculate what torque and/or horsepower a vehicle will produce at the wheels. There are quite a few other methods, but none generally accepted at more accurate.

What an engine produces at the crankshaft and what it puts to the road are two different things, with losses created by accessories, transmissions, etc.

[Valve Bounce]

In terms of accurate measurement, a dyno is the best way to calculate what torque and/or horsepower a vehicle will produce at the wheels. There are quite a few other methods, but none generally accepted at more accurate.

.


You could try one of those programs you download from the internet onto a dual core laptop with a minimum of 4 gigs of memory and using a Logitech gaming mouse, you connect a Motorola mobile phone to the laptop and point it at the F1 car screaming down the track. Then you use the camera function and take a picture, then using your downloaded program, you extrapolate the BHP of the machine.

I am not sure exactly how this works, but you could ask Daniel to explain it to you.

[leopard]

I could be wrong but usually they are used differently.

KWatt usually used for measuring power resulted from any mechanical source of electricity for relative permanent installation purpose.

While horsepower used for measuring potential power of anything movable (car or automotive term) resulted from the mechanical source of power.

[Magnus]

Youre right to a certain degree lepslep, (argh, your name is so looong) but this have never been a formal way of deciding where to use kW and where to use hp. As it is today hp is not an SI unit, but most manus still displays it as people are used to it.
It is when you are abt to start calculating around it is good if you use SI-units, because it simplifies things a lot, and you can also "calculate" with the unit so that you get a proper one out in the end.

[LeonBrooke]

Youre right to a certain degree lepslep, (argh, your name is so looong) but this have never been a formal way of deciding where to use kW and where to use hp. As it is today hp is not an SI unit, but most manus still displays it as people are used to it.
It is when you are abt to start calculating around it is good if you use SI-units, because it simplifies things a lot, and you can also "calculate" with the unit so that you get a proper one out in the end.

In New Zealand and Australian sources that I read they use kilowatts for cars and it's confusing...

[cosmicpanda]

In New Zealand and Australian sources that I read they use kilowatts for cars and it's confusing...

oh, it is.

[leopard]

You must have read wikipedia for the source.

[MrJan]

You can judge horsepower by looking at how fast the car goes and saying "there's no way he only has 300hp in that" ;)

[michael_is]

You can judge horsepower by looking at how fast the car goes and saying "there's no way he only has 300hp in that" ;)

Must be a 6th sense that I don't have :confused:

[Magnus]

Must be a 6th sense that I don't have :confused:

If you have the slightest interest in cars and can sort a Datsun from a Veyron I think you have the 6th sence aswell :)

[MrJan]

Indeed, it all comes from experience and watching cars. Without rallying I still wouldn't have a clue :D

[airshifter]

You can judge horsepower by looking at how fast the car goes and saying "there's no way he only has 300hp in that" ;)

But, it might be massive torque too.

They had some diesel drag racing stuff on over the holidays. Guys were running 9's in the 1/4 miles in street legal trucks. :D

[Magnus]

Yep. It is truly amazing. When I studied we visited GIK turboteknik in Ljungskile on the west coast of sweden, not far from where I live.. They amongst other projects supply the swedish rally cross ace Kenneth Hansen with power and mostly worked with garret, as I recall it. Btw read the book Cosworth: The Search for Power, if you have the slightest interest in the mysteries of internal combustion engines.
Anyway; they told us abt their tractorpulling project in wich they had a boost pressure of 16 bar. that is 232 psi. I think it was a Scania v8, might have been a cat aswell though. My memory is not all that good...
They said it was really difficult to keep the heads on the block...
Strange...

[MrJan]

But, it might be massive torque too.

They had some diesel drag racing stuff on over the holidays. Guys were running 9's in the 1/4 miles in street legal trucks. :D

If it sounds like a truck and sprays out black smoke it's probably diesel and therefore torque, if it sounds good and smoke is absent then it'll be good ol' petrol and HP :D As basic as basic can be but it's a general rule of thumb I find very useful.

[Daniel]

You could try one of those programs you download from the internet onto a dual core laptop with a minimum of 4 gigs of memory and using a Logitech gaming mouse, you connect a Motorola mobile phone to the laptop and point it at the F1 car screaming down the track. Then you use the camera function and take a picture, then using your downloaded program, you extrapolate the BHP of the machine.

I am not sure exactly how this works, but you could ask Daniel to explain it to you.
I can? :mark:

[MrJan]

Yes you can. Go on :D