[QUOTE]Originally posted by no really

 

The S2000 can hang with the 2004 V-8 S4 untill about 70-80mph where the S4 pulls ahead. The S-2000 and S4 have almost identical 0-60 times but the S4 has quattro, which helps it out of the hole. If the S2000 driver can jump out of the hole faster he has an advantage but will probably still lose.

 

[QUOTE]Originally posted by Zoran

 

 

Not sure why this thread was resurrected after over 3 months, but apparently it deserves revisiting.

Can we agree that the work an engine performs can be measured in terms of pounds of thrust? And thrust is what accelerates a mass?

Pounds of thrust is determined by multiplying the torque output of the engine (in lb-ft) by the gear multiplication (both transmission and differential) and the parasitic loss (say, 20% for autos and 15% for manual transmissions), and then dividing by the radius of the wheel, in feet.

So:
thrust in pounds = engine torque in lb-ft * transmission gear ratio * differential gear ratio * 0.85 / radius of tire in feet

You need to graph this for the entire power band to compare two vehicles adequately, if that's your goal, as internal combustion engines don't produce the same amount of torque at all rpms. The more data points you plot, the more accurate your model will be. So dyno graphs for each car would be necessary.

You can use horsepower numbers at each rpm to calculate thrust values, but you need to convert horsepower back into torque before doing the gear multiplication and radius division. So, an easy way to compare the thrust of cars with identical transmissions and rear gears is by comparing torque numbers, the only variable in the equation. When you start comparing different transmissions and rear gears, it gets more complicated, but I think we can agree that it will take the same amount of thrust to accelerate 3000 lbs at a given rate, regardless of whether it says BMW or Ford or Honda on the back. So, unless one of the cars has a radically different gearset (a la S2000), you can usually compare the potential acceleration of different cars by comparing torque values and weight, or hp/weight ratios, which really amounts to the same thing, after you do the math.

[QUOTE]Originally posted by Destiny2002
Torque is not energy.

 

wow, 13 pages of all this. im not gonna read through all of it cuz damn, i dont have that kind of time. but i will chime in with my 2c as simply as i can.

forgive me if i am just repeating things, but thinking in physics, the only thing that can cause acceleration is a change in force. torque is a force. therefore torque causes acceleration. hp is a measure of energy and has a factor of torque in it, but is presented over time (in this case rpm). so in that sense, both contain forces, so both can change acceleration; just differently. now, which one producing more is dependant on the variables of how much torque and how fast its spinning. the ideas of peak or max hp and tq though, are completely meaningless. you would have to know the instantaneous tq at any given point (or at least enough points) to make any real use out of this information for comparing.

 

Read my post, at the end of page 13. If it is not clear, lemme know.

 

 

I guess I don't understand how one could make a statement like the one above, and then assert that horsepower is the only number that is important in accelerating the car.