t.henss,

You're correct, you feel the acceleration, neither the torque nor power. Humans also sense acceleration change (second derivative of velocity, usually in meters per second cubed, also called "Jerk").

Physically, the acceleration comes from the propulsion force at the tire patch (which, when vehicle speed, trans and tire gearing are known, then the engine torque producing this force is known). The Jerk is how non-linear this acceleration is.

Humans percieve a constant jerk and gradually increasing acceleration as "fast". Zero jerk and constant acceleration can, in some cases, feel slower but result in quicker overall acceleration.

If I get some time, I'll resurrect some graphs I did for a Vehicle Systems class I participated in showing the difference, but let me try to tell you in words:

If you have a motor (like and electric motor) that has a constant torque throughout the entire range of useage, say from 0-60 MPH, you have a vehicle that will accelerate at a constant acceleration. If you have the correct torque to produce the tirepatch force that results in about 0.45 g's of accleration for your mass, your electric vehicle will get to 60 MPH in about 6 seconds.

BUT, it will not FEEL very fast. This is because people acclimate to acceleration very quickly. Physiologically, the body can acclimate to a new acceleration in about a third to a half a second - the body senses increasing forces, when the forces stop changing (like in your seat back), the body acclimates and settles in - for another 5 1/2 seconds, even though you are gaining speed quite quickly. Throughout the entire period of acceleration, you experience an acceleration of a constant 0.45 g, and a jerk of zero. The average acceleration is the same, about 0.45g, and the peak was pretty much identical: 0.45g. The speed just increased at a constant and linear rate right up to 60 MPH.

The power curve for the motor is basically linear and increasing - right up to the max power rating of the motor. After which the torque drops in proportion to increasing motor speed.

If this vehicle is powered by an internal combustion engine, this torque has a function that looks a bit like a logorithmic function, with some secondary term. Some torque curves are very linear at the beginning, then "curl" over. Turbo curves tend to be linear up to max torque, then somewhat flat topped as the boost controller kicks in... Superchargers tend to be linear on the lower end - a kind of blend between N/A or Turbos (yes, they DO feel different) Bottom line: the torque is not CONSTANT with respect to vehicle speed.

This means that the tire patch thrust is not constant - and since the thrust is changing, so is the acceleration. If this the acceleration is changing and increasing, the occupants experience "jerk".

If this theoretical IC vehicle is set up to coincidentally have a constant jerk of around 1.47 m/s^3, this vehicle will get to 60 MPH in 6 seconds too. BUT it will FEEL much faster. This is theoretical, but at the end, the velocity is increasing non-linearly and acceleration is approaching 0.90 g. If you look at the curve of acceleration, it starts low, you're only pulling about 0.14 g at 1 second, matching the electric motor vehicle (0.45g) at about 3 seconds, and your body experiences this "rush" of change in acceleration we all associate with speed.

So, for internal combustion engines, BOTH power and torque are important. Peak power, since most internal combustion engines operate in similar manner, has THE SINGLE MOST CORRELATION WITH ACCELERATION. Since we associate acceleration with speed, and we all feel the need for "speed", we all really want power in an IC motor.

However, there are exceptions to all of this: low end torque is good to have, high redline is good to have, because the higher the torque, the higher the acceleration that can be maintained. Low end torque gets us moving and gives us that initial "oomph" when driving below the peak torque RPM of the engine. Hi power at hi RPM's means this torque curve is still increasing through a large range - allowing us to experience increasing tire patch thrust for a greater speed range. If you get to use all of the engine and have great range of coverage in your transmission, and you really care about ET's and 0-60's, you ALWAYS WANT HIGH POWER.

**I suppose you can also sum it up like this: The torque curve tells you at any point what the acceleration is (torque translates to force at tire patch which = acceleration). The power curve for a motor is nothing more than the time derivative of the torque curve. The vehicle jerk is nothing more than the time derivative of the vehicle acceleration. And since we associate "jerk" with "percieved speed", the more jerk, the faster the car will feel (and actually be, due to the non-linear nature of the torque curve). To get more jerk, you need more power.**

Bottom line - you want more power. Even though engines are really torque devices.

If you still don't buy this, look at a diesel engine. Great low end torque. But a scant few thousand RPMS above this, you reach a lackluster peak power and decreasing torque (even turbocharged diesels). This means you need a multitude of gears, or a continuous transmission, to maintain this torque (or tire thrust) over a large speed range (say from 0-60).