Ok I have a working theory in my head. It goes as follows. Hp gives you a rough wager on a car's top speed and torque gives you a rough wager on a car's thrust/acceleration.

Now I'm going to try and somewhat prove this using very basic physics. If my reasoning is flawed someone please call me on it.

The following is in Metric units cause, well, English units suck.

ok HP is Rated at kWs Those are KiloWatts if you're interested. Kilowatts are a measure of power. Now what is power? Power is work per time unit in this case 1 kW= 1 kJ/s. A kilojoule is a measure of energy. Now energy represents several things and in this case could represent kinetic energy. Kinetic energy is just how fast an object is moving. the equasion for kinetic energy is E = 1/2 mv^2. m being the mass and v being the velocity. So from the top.

1 kW = 1 kJ/s (pick an arbitrary time of 1 sec and multiply it to cancel out the seconds)

1 kJ = 1000 J = 1/2 mv^2 lets give the car a mass of 2000 kg

(1000 J*2)/(2000 kg) = v^2 Square root after you're done with the math and you get

1 m/s So that's my wild ass theory on hp


Time for torque.

In metric torque is measured in N*m. N is Newtons which is a force and m is of course meters. 1 N = 1 kg*m/s^2. m/s^2 is in fact acceleration of an object.

So you take the N*m divide by the distance travelled, lets say 1 m. You get just Newtons. Divide that by the mass of the vehicle and you now now how fast the car is accelerating over that one meter.

Of course this is all so simplified its impossible to say "This much hp goes this fast". Really all it is for average car guys like me is just a guesstimate of a car's feel. High hp and low torque is zippy but doesnt pin you in your seat nessisarily, and if torque is higher and hp is lower then the car accelerates hard but might run out of breath at higher speeds.

Now none of this is taking into account the actual curves either so in reality this probibly is only confusing you further. But its my theory at least. Hp = speed, torque = acceleration.

I took a large chunk out of my life to come up with this formula= ((car weight in pounds)/(HP + ft.-lbs.)) *.68 +1.4

Gives a pretty decent estimate of 0-60 time.

Nope, gearing determines top speed.

Horsepower is a derivitive of torque.

Sorry I edited your post, new mod powers means edit is where quote used to be

Anyways as I was saying. Gearing also determines thrust and acceleration so in reality a different gearbox could change everything. But if you took two cars with identical transmissions you would probibly see the same results I just described, the car with more torque would accelerate faster and the car with more hp would have a higher top speed.

Edit: Torque is also a derivative of hp you just use RPMs to convert the two

I used your formula .... came up with approx 8.0 seconds for my current ride ....dead on accurate.

Also calculated 7.3 seconds for my old ride .... also very accurate.

There are exceptions to it, but it's pretty solid. I used data from a hundred or so cars and graphed it in excel to get a good curve. Funnily enough, the car farthest off the graph is my own.

The reason why probibly is because Volkswagen quotes its horsepower numbers extremely close to what the wheels are putting out, most other car makers just quote what the engines put out.

The funny thing is that, when you do the math on my car, that's what VW claims it'll do (7.5 seconds pretty much) but in reality it's good for about 6.5 or even less (even down to 6.2 with a really great driver at the helm.)

And yes, you're right, rumors abound that the 180 HP 1.8T is really 200+.

I found an accurate conversion for american figures (ft-lbs and HP) that goes

Horsepower=(tourque*RPM)/5252

Yes, that is the formula for HP.

Doesnt europe use 5500 instead of 5250? At least the UK does I mean. Which means their numbers are always a little shy of the US's's's's's

What on earth are you talking about??? 2250!?

The Cliff's notes.


HP Vs. Torque as explained by Car Craft. Read it, Love it, Live it

That's a pretty good site...I never knew where the 5252 number came from before.

5500.. So I was 3 grand off...

with your formula my car does 60 in a screaming 12.24 seconds. excuseme while i go off and cry in a corner

that gives my car 6.2 seconds. i can do better than that!

Yes, the WRX is one of those cars that doesn't adhere to the formula to well.

AWD Probibly throws it off.

I think it's just some cars magically don't follow the formula. As I said before, the GTI is farthest off from the formula that I've seen so far (formula says it's good for 7.1 but it's really more like 6.3)

Ha Ha clark I was right. Your equasion is just geared for engine hp and torque numbers. I did a rough estimate and adjusted the GTi's hp and torque to 200 and 194 respectively and i got 6.5 sec.

God damnit I'm awesome.

Considering the equation only deals with engine and car weight it's disturbingly accurate. Any and all differences between the formula and the actual I attribute to weird gearing and/or weird aerodynamics and/or odd test conditions.

Well 60 miles per hour no matter how you change it isnt really *that* fast in today's world. It makes sense because you have X amount of power being put out by the engine so obviously under ideal conditions its going to go so fast. Makes sense to me.

It crossed my mind that aerodynamics doesn't make a huge difference under 60 MPH, which is why I developed a formula to estimate 0-60 but gave up on one for the 1/4 mile.

The number of "Horsepower" is calculated by how many "foot/pounds" of work can be done in a given timeframe.

You can get an idea of how a dynamometer works in the following way: Imagine that you turn on a car engine, put it in neutral and floor it. The engine would run so fast it would explode. That's no good, so on a dynamometer you apply a load to the floored engine and measure the load the engine can handle at different engine speeds. You might hook an engine to a dynamometer, floor it and use the dynamometer to apply enough of a load to the engine to keep it at, say, 7,000 rpm. You record how much load the engine can handle. Then you apply additional load to knock the engine speed down to 6,500 rpm and record the load there. Then you apply additional load to get it down to 6,000 rpm, and so on. You can do the same thing starting down at 500 or 1,000 rpm and working your way up. What dynamometers actually measure is torque (in pound-feet), and to convert torque to horsepower you simply multiply torque by rpm/5,252.

Blatently stolen from http://auto.howstuffworks.com/horsepower.htm

Yes I'm aware of how horsepower is obtained an all that good stuff but if Horsepower is just taken from torque and RPMs then why dont people just measure it in torque then? I still stand by my broad generalization that cars with monster loads of torgue and few rpms (so less hp) have better acceleration and cars with little bits of torque but loads of rpms (More hp) have a higher theoretical topspeed.

http://auto.howstuffworks.com/question622.htm

Ok I know.

because horsepower sells more cars than torque does.

as for your broad generalization, torquey cars do have better acceleration at low speeds (i.e. off the line). cars with high horsepower tend to have higher top speeds, yes, but also have better acceleration at high speeds as well. so a high horsepower car will accelerate faster than a high torque car when they're trying to go from 50mph up to 70mph, assuming the gearing is set up for each respectively. of course if you put the car in top gear and did the same thing, the torquey car would be faster. also the high revving, high horsepower car spends less time shifting as it climbs from 0-60+, making it ideal for road racing. torquey cars are good for autoX

as my brother so wisely points out, "horsepower sells cars, torque wins races."

Which is bullshit. Otherwise F1 cars wouldnt be the kings of motorsports with their 3 liter 18000 to 21000 RPM engines.

Well, racing's a bad example...but I mean, he has a point. Perhaps a better saying would be "horsepower sells car, torque is what makes 'em perform"

again the RX-8 can still perform in a straight line even though they have like no torque. Probibly the most accuracte responce would be "Horsepower is what you buy and torque is what you feel"

Yeah, that's more like it. And why is the RX-8 an F1 car???

d'oh gotta fix that.

too bad you have to launch the RX-8 at 8,000rpm to get their claimed 5.9s 0-60 time

Why's that too bad?

Interesting thread.

Too bad i failed physics in high school

it is if you wanna go that fast day to day.

Well, who says day to day you have to cook off the fastest 1/4 mile time you can?

i do

Well in that case too bad the RX-8 is a rotary engine and it can withstand those kinds of stresses in day to day life where a piston engine will eventually fail you.

but the tires will not, and that, my friend, is where you need low-end torque. rotaries do have less stress to deal with, but historically they have leakage and emissions problems. hopefully the renesis will change that.

horsepower= torquexrpm/5250

thats about all i know. For converting kilowatts to horsepower, im just lazy and use proportions of a known value set . Like 300kw (Holden HSV GTS-R 300)=402.5 horsepower. So i set up (300/402.5)=(225/x) if im trying to find how many horsepower 225 kw is.

soo

300 225
----- = ----
402.5 x

402.5x225=90562.5
90562.5/300=301.875

pretty neat eh?

im still trying to find a propotion to determing lb-ft from nM, but the truth is I just dont' care enough. Oh, well.

1.483 Nm = 1 ft.-lb.