Torque

[D4LY]

ibiza cupra tdi has the 160 bhp engine! imaging the power to weight/torque to weight ratios.

AYE KLASS 160BRAKE....WAT ENGINE IS THAT IS IT THE 2.0TDI THAT AUDI AN VW HAVE STARTED USEN IT MUST BE SCAREY QUICK IN SUCH A SMALL CAR

 

[brendy]

1.9 pd tdi

 

[D4LY]

1.9 pd tdi

OH ..U LEARN SUM FIN NEW EVERY DAY 160BHP :lol:

 

[Chrismac]

ibiza cupra tdi has the 160 bhp engine! imaging the power to weight/torque to weight ratios.

Picking my Ibiza Cupra 160 up any day now, it arrived last Thursday and I called over to the dealers to have a look and it looks well. The salesman said it will be ready to collect around the start of the week so hopefully tomorrow (Tuesday), eagerly awaiting his phone call.

 

[brendy]

agnews by any chance? i wouldnt use any other dealer for seat.

 

[Chrismac]

Yep, the new one on boucher road, first class service and I got an exellent deal. Agnews at Ladas drive never really seemed to interested in selling me the car. I was told that there would be a very long delivery time because the car was only out, and they where not willing to knock anything off the price. They told me that they would phone me later that day with some details and I am still waiting (two weeks). I was advised to go to their new dealership at Boucher and it was totally different, I was told that there where several Ibiza Cupras in stock and within a day the car was ordered and I got a much better deal than expected, the staff are very friendly aswell and couldnt be more helpfull

 

[al-sw20]

In most cars maximum torque is produced at fairly low revs. it is a myth that torque is a measure of low down power, this is not true! torque is the ability to change horse power into movement.

And the higher in the rev range that the torque is produced the better because u can take advantage of gearing!!

Mate you are all theory.

Torque, very simply put is the twisting force around a point of rotation. The simplest example of torque is imagine a wrench. Let's say that the wrench is 2ft long. So you put the wrench on a bolt and you exert 75lb of force on that wrench. How much torque is being exerted on the bolt? That is, how much twisting force is exerted on the bolt? The answer is 2ft * 75lb = 150ft-lb of twisting force or torque. Now if you got out a wrench that was 3ft long and exerted the same force you would exert 3ft * 75lb = 225ft-lb of torque on that bolt. To get exactly the same effective torque on that bolt with a 1ft wrench you would need to apply 225lb of force! So despite all the generalizations of torque (and often wrong) concerning cars, remember that the twisting force is all the torque is.
Now, you can work backwards to figure the reverse. That is, let's say you put that 3ft wrench on the shaft of an electric motor. Suppose the electric motor is rated at 225ft-lb. How much force must you exert on the wrench to keep it in place? Simple since the equation for torque is torque = force * leverarm then force = torque/leverarm. So in that example it is force = 225ft-lb/3ft = 75lb. With this understanding we can now approach torque's application in a car.

In a car the key parts that make up the drivetrain are the engine, gearbox, differential and driven tire. The thing we are interested in is the acceleration of the car. You have probably heard the equation F=MA. This means Force = Mass * Acceleration. Solving for acceleration we have Acceleration = Force/Mass. Now, let's investigate the acceleration of a mx5. We already know the mass. With driver, let's say the mx5 weighs 2500lb. We can also term this as 2500lb mass. We will also use the force in terms of lb. If we use those units in our previous equation we will get acceleration in terms of G units (gravitation units). 1 G unit is equal to an acceleration rate of approx 22mph for every second that passes. So now let's look at how to calculate the force propelling the mx5. You first start at the engine. Let's suppose the engine is at torque peak and thus at 5500rpm. The engine makes 125ft-lb. Now we follow the torque path through the drivetrain. We are using the standard 5-speed which has gear ratios of 3.14/1.89/1.33/1.0/.81. The gear ratio means how many times the input shaft turns to make the output shaft turn once. So in 1st gear the input shaft from the engine turns 3.14 times to make the driveshaft connected at the rear of the transmission turn once. This in effect multiplies torque by the said gear ratio. So we have 125ft-lb * 3.14 = 392.5ft-lb of torque at the driveshaft. Now the torque enters the differential. Same thing occurs. The differential has a ratio of 4.3:1. So the torque exiting the differential and thus turning the halfshaft to the driven wheel is 392.5ft-lb * 4.3 = 1688ft-lb of torque! Now that sounds like a lot of torque! However, to calculate the force the is actually propelling the car one must consider the radius of the tire. The tire is about 23" tall. Its radius is therefore 11.5". Converting to ft. that is .958ft. Remember the above example with the wrench? Force = Torque/Leverarm. The tire radius is the effective leverarm. So we have Force = 1688ft-lb/.958ft = 1762lb. We now have the force propelling the mx5. Thus the acceleration = force/mass = 1762lb/2500lb = .705G.

Now what happens in second gear? Let us look at the concise form of what we just figured for first gear. It is

Accel = T * G * D / R / W

where:

T = torque at engine
G = gearbox ratio
D = differential ratio
R = radius of driven tire
W = weight

So for 2nd gear we have:

Accel = 125ft-lb * 1.89 * 4.3 / .958ft / 2500lb
Accel = .424G

And now the other gears:

3rd:
Accel = 125ft-lb * 1.33 * 4.3 / .958ft / 2500lb
Accel = .298G

4th:
Accel = 125ft-lb * 1.00 * 4.3 / .958ft / 2500lb
Accel = .224G

5th:
Accel = 125ft-lb * 0.81 * 4.3 / .958ft / 2500lb
Accel = .182G

OK, so now you see what the acceleration is in each gear when the engine is making 125ft-lb of torque. Now, note for simplicity sake I have also neglected rolling and aerodynamic friction, drivetrain efficiency and rotational inertia. At this point they would just confuse the matter.

Now, since the acceleration is by far the greatest in 1st gear, why wouldn't we just stay in 1st gear the whole time? You already know the answer to this. That's right, you can only go so fast in 1st gear. You run out of rpm. At about 35mph you are hitting the redline and now to go any faster you must put it in second gear. You can see from our simple equation the acceleration will now drop. This is where the concept of horsepower comes from. In this case it is speed dependency of torque. In fact the engine doesn't always make 125ft-lb of torque. That is what it makes at 5500rpm. As the rpm climb, the torque drops. Now, since we know the gear ratios and tire size, we could create a chart showing the engine vs. mph in each gear. With that information, and with no concern for horsepower, we could plot the acceleration of the car in each gear as a function of mph. So why even bother with hp? Because it is a way that humans can better understand the performance potential of a car.

If we don't consider speed at all, it seems you could simply make a huge amount of force propelling the car by selecting a gear ratio like 1000:1. And in a sense you would be correct. You would have:

Accel = 125ft-lb * 1000 * 4.3 / .958 / 2500lb
Accel = 224 G !!!!!!!

Wow!!!! However, consider this: The car would hit redline at about 0.1 mph!!!! Now let's suppose we have a continuously variable gear ratio. I would keep reducing the gear ratio so that the car can continue to go faster. As speed increases the acceleration will be slower because the needed gear ratio will be lower. Remember in the previous example, I didn't even mention the corresponding speed in each gear at 5500rpm? Well here is the speed in each gear at that 5500rpm.

1st: 27.9mph
2nd: 46.3mph
3rd: 65.8mph
4th: 87.5mph
5th: 108.0mph

That means we would have the following acceleration rates at the given speeds.

.705G : 27.9mph
.424G : 46.3mph
.298G : 65.8mph
.224G : 87.5mph
.182G : 108.0mph

Now, by continously varying the gear ratio, imagine we simply are connecting the dots. That is between 28mph and 46mph the acceleration is dropping from .705 to .424, from 46mph to 66mph it is dropping from .424 to .298, etc. What does this mean? You are now understanding hp. Hp is speed dependent. Hp is actually just a specific unit measure of power. Power is defined as Force * Speed. Hp = 550lb-ft/sec BTW. So how does power relate to acceleration? Solving for Force we get: Force = Power/Speed. Substitute this into the Acceleration equation of Accel = Force/Mass we get Accel = Power/Speed/Mass. We can also turn that around and solve for Power. That is Power = Accel * Speed * Mass. Let's now calculate the power for the acceleration rate in each of the 5 gears. To make things simple I will convert mph to ft/sec. You will see the reason later:

.705G : 40.9ft/sec
.424G : 67.9ft/sec
.298G : 96.5ft/sec
.224G : 128.3ft/sec
.182G : 158.4ft/sec

To calculate power for the first one:
Power = Accel * Speed * Mass
Power = .705G * 40.9ft/sec * 2500lb
Power = 72086ft-lb/sec

Remember that hp = 550ft-lb/sec?
So...
Hp = 72086/550 = 131

Now let's calculate for the rest of the speeds:
Hp = .424G * 67.9ft/sec * 2500lb /(550ft-lb/sec)
Hp = 131!

Hp = .298G * 96.5ft/sec * 2500lb /(550ft-lb/sec)
Hp = 131!!

Hp = .182G * 128.3ft/sec * 2500lb /(550ft-lb/sec)
Hp = 131!!!

Hp = .298G * 158.4ft/sec * 2500lb /(550ft-lb/sec)
Hp = 131!!!!

Look at that! Hp is constant at all speeds. Now there is one final piece to complete the puzzle. Hp can be figured in terms of torque. The solution is a little longer than I would like to add to this already long post. It is:

Hp = Torque * Rpm /5252

That's it! Despite all the folklore, hearsay and general B.S. you might hear about Hp and torque, there relationship is completely describe by this simple equation. Now remember, we were using 125ft-lb @ 5500rpm? Let's calculate the hp at that rpm. Hp = 125ft-lb * 5500rpm / 5252 = .... guess? That's right 131hp!!! Just like it was calculated the "long way" above. This is the reason we are all concerned about hp. It shows the acceleration potential of a car as a function of speed without having to know the gear ratios or other complexities. That is, if all one knows is hp and weight, one can have a pretty good idea of the acceleration a given car will have. Of course this is not the only thing... there are LOTS of other factors.

So now, what does torque and hp mean for a car? I think you can figure that out now. When the car is at a standstill the best acceleration will be achieved by raising the engine rpm to the peak torque rpm, putting the gear in 1st (highest gear ratio... we are at 0mph) and taking off. So that is what the torque is good for... taking off. Once the rpm increases the driver will shift gears so as to maximize hp at all times. Hp will determine the acceleration. Well, as you now know, torque * gear ratio * diff ratio .... etc. etc. etc. also does the exact same calculation, but it is just as accurate (and a lot easier) to simply view it as acceleration = hp/speed/mass. Hp will also ultimately determine the car's top speed. That will occur when the forces opposing motion (aerodynamic and rolling friction) equal the force propelling the car. I won't go into that solution here, but suffice to say it is very similar to what we just solved for acceleration above... it is just a special case where acceleration = 0.

There are other useful things that horsepower and torque allow us to figure when it comes to the real world performance of a car. That is, if you look at the rpm that they occur, you can get an idea of where the engine will be in the powerband. The powerband usually starts between the peak torque and peak hp rpm and ends somewhere above peak hp rpm or redline (whichever comes first).

 

[brendy]

jesus H.
did the hero save the dog in the end? i fell asleep half way through!

 

[Max]

jesus H.
did the hero save the dog in the end? i fell asleep half way through!

:lol:

 

[D4LY]

*** me wat did u swallow :lol:

 

[Kerzo]

oh dear i read that all

 

[streetcar]

Who's all theory, I think most people would have understood wot i said alot easier than that garbage!!

Wot site did u pull that from? did u even read it urself?

 

[VEN©M]

well done, seems he's good at copy and paste and there really was no need or call for it..

seems we all know what torque is now.