kreativ

What's the performance difference between two engines with these power #s?
1. 230 hp, 210 lb-ft torque
2. 210 hp, 230 lb-ft torque

JBrady

This is a question that has been discussed many many times on many many forums... nevertheless, it is rarely understood. The majority claim torque (force) is the only thing that matters because horsepower (power) is only a calculation. Without getting to complex the important thing to remember is that there is ALWAYS a torque AND a power figure for any given rpm at WOT (wide open throttle) be it 2000, 3000, 4000, 5000, 6000rpm or ANY other rpm. Peak power and peak torque occur somewhere in the range. Torque always peaks before power. Horsepower and torque are ALWAYS the same number at 5252rpm but are different things. Torque is how much force is available at any given instant. Power is how fast that force is made available.

Now, the critical factor is that force (torque) can be multiplied with gears. Power (HP) can not. Changing rear gears (or tranny gears) can yield more torque but power is not increased. All things being equal (vehicle weight, rotational mass, traction, etc) the engine with the highest AVERAGE power rating will be the fastest accelerating. Average meaning the rpms used with the gearing. This is generally a 2000-3000rpm operating window near an engines redline. A very peaky engine may have more peak HP but another engine with less peak power could have a higher average power over the above described operating window.

Now, since I probably told you more than you wanted... does this help? If not ask more questions, I will try to explain in plain english.

kreativ

hehe, I think I got the jist of it. Thanks.

VSsc400

iTrader: (1)

Horsepower vs torque
here is the formula

1HP = 33,000 ft/lb over 1 minute time or
1HP = 550 ft/lb over 1 second of time
Torque is the force that roates things.
Torque = force * distance from the center or radius
60 = number of seconds in 1 minute

Horsepower can only be measured distance covered
Torque can only be measured in rotation force

thats why they tell us HP and torque


here is the formula
(Torque * engine speed)/5252 = horsepower

the number 5252 is derived by 550/((2*pi)/60) = 5252

example of 1992 lexus sc400

(260torque*4400RPM)/5252 = 217.821HP

of course the dynanometer or DYNO shows shows a graph that shows HP going from 0HP to 250HP because you need to cover distance to show HP and since there is no straight line distance covered at the very moment you slam on the accelerator.

Lets take the 2001 Honda S2000 as example
(153torque*7500rpm)/5252 = 218HP

so to settle the argument. There is no such thing as more important. They first measure torque and derive the horsepower. The higher the engine is able to revv the more horsepower it is able to generate (discounting friction etc). But due to engine inefficiency, friction, ability to deliver fuel and air etc torque and HP top off at different points..Therefore if your maximum torque is low you need a high revving engine to create more power. Since it takes time for an engine to revv up the more torque you have the more power you will have initially.

so to compare the top 2 examples when the S2000 reaches 7500rpm it will start going faster than the SC400 @ 4400rpm if both cars weigh the same


Dennis Lee