Originally Posted by rlchv70:
You can't have 300hp and 300 lbft at both 3000rpm and 6000 rpm.

300 lbft @ 3000rpm = 171 hp.

300 lbft @ 6000rpm = 343 hp.

hp = torque * rpm / 5252.

Horsepower and Torque
by Matthew Kramer :
Take two engines, one that develops 220ft-lbs from 3,000 RPM to 6,000 RPM and one that only holds its 220ft-lbs of torque from 4,000 RPM to 5,500 RPM. Beyond those ranges, both engines fall off quickly. While they have the same torque from 4,000 RPM to 5,500 RPM (meaning they will accelerate at the same rate then), from 3,000 to 4,000 RPM and 5,500 to 6,000 RPM the first engine has more torque and will therefor accelerate faster. In a race that takes each engine from 2,000 RPM to 6,500 RPM, the first will clearly win, despite the fact both owners can boast about having 220ft-lbs of torque.

Once again, though, it needs to be noted that a car's quoted power is at one specific place in the engine's range of operation. Let's say it takes a certain car 160HP to go 120mph and 200HP to go 150mph. The manufacturer claims the car makes over 200HP at 6,500 RPM. As luck would have it, this car's gearing is set up so that it travels 150mph at 6,500 RPM, which would lead one to believe that this car can do 150MPH, since it has enough HP to reach that speed. However, through lack of engineering, the gearing is setup so that the engine runs at 4,000 RPM at 120mph, and it is only capable of 150HP at 4,000 RPM. The car could never hit 150mph, because it doesn't have the power in the right place to climb pass 120mph.

As RPMs get higher, there is less torque for a given amount of power. For example, compare two engines that make 250HP at their peaks. The first peaks at 5,000 RPM, the second at 7,000 RPM. At the time the first engine is making its peak horsepower, it will be making 263ft-lbs of torque. Where at its power peak, the second engine only makes 188ft-lbs of torque. Even though both engines boast the same peak power, the first is going to have higher torque the majority of its power band, meaning quicker acceleration. This is complicated some by gearing, though, as the second engine has a much longer range of operation before it needs to shift to a slower gear.

Conclusion:

A car's performance isn't as cut and dry as simple peak horsepower and torque statistics. It's mainly a result of the area under an engine's torque curve, a car's weight, and its gearing. Horsepower, it turns out, is really only useful as an indicator of a car's top speed. However, because of the relationship between torque and power, horsepower can also be used as an indicator of the engine's torque band. In the real world, though, the best way to figure out a car's performance is to drive it, or read results from others who have driven it.