[ryker]

Originally Posted by habitat

Your beloved "flat torque curve" is due to the performance cam switch. Maybe you failed to realize that 100% of dyno charts show torque tapering down after it's intersection with the HP curve @ 5252rpm? So if you can imagine the K20Z3 using only the performance cam profile from 0rpm-8000rpm, you'd see the max torque peak sooner then take a dip at 5252RPM. Why? MATH BUDDY.

Power refers to Horse power. Torque refers to rotational force. Drive an old Diesel mercedes, you'll get it through your head why HP and Torque figures complement one another.

Class is about to begin:

Originally Posted by ryker

Accelerating a Car

Newton's second law of motion states that the acceleration of a body is related to the force being applied and the mass of the body, as seen below:

Newton's second law of motion. A greater force or a lower mass will result in a greater acceleration.


In order for there to be any acceleration, the force must be applied at the same speed that the object is traveling, for a non-zero length of time. A force being applied at a certain speed for a period of time is power, therefore, the acceleration force on a moving object is determined by the power being applied at that speed.

The wheels receive torque and rotational speed from the engine, and lay down a force onto the pavement. It is this force which accelerates the vehicle. The car's speed is determined by the rotational speed of the wheel.


The acceleration of a moving car is equal to the power divided by the speed and the mass. The product of speed and mass is known as momentum.

The acceleration force of a car comes from the torque at the wheels. This is why the acceleration is often calculated from engine torque by using the large formula seen below:


The acceleration force can be calculated by passing the engine torque through the entire drivetrain to the road.




The acceleration force can be calculated by passing the engine torque through the entire drivetrain to the road.



If the speed of a car and the power of its engine is known at a given instant, the force of acceleration can be calculated without knowing anything about the drivetrain gearing, tire diameter, or even the engine torque, as demonstrated below using imperial units:

When the power and speed are known, the acceleration force can be calculated directly without knowing anything about the drivetrain.



The torque method and the power method will both produce the same results, as seen in the example below.



The calculated acceleration force is the same when using the torque method or the power method.

Shaft power is the product of shaft speed and torque, and the speed and torque can be altered proportionally using gears. (Honda matched this perfect on the Si) If we want to apply a lot of torque to a shaft that is rotating, a lot of power is needed. The more power the better. However, the power must be accessible from all vehicle speeds, which can only be accomplished by producing a lot of torque throughout the rev range, or by having a transmission with many gears. (try 6th gear WOT at 70mph then downshift to a higher alter gear like 3rd) It is this fact that has spawned phrases like "Torque is King", or "Horsepower sells cars, but torque wins races", which can be misleading. Torque on its own isn't useful in accelerating a vehicle, because it is not at rest; it is moving. Therefore, power at the wheels is what matters. Cars are often described by their power-to-weight ratio, not their torque-to-weight ratio.
The vehicle with the largest average acceleration is the one that has the largest average force going to the pavement through a wide range of speeds. Which is why a turbo car or v8 is easier to drive than the low torque 4 bangers.

" Peak power sells cars. High average power wins races. "


Honda knows this and does an awesome job on BOTH the r18 and Si by providing a flat torque band that is useable throughout the entire RPM range and by using a close ratio 6-speed in the Si.