Why isn't the Prius slow?

A typical internal combustion engine makes the most power near Redline and the most torque near the middle of the RPM range.



However, a typical electric motor makes the most torque near 0 RPMs, and Power tends to be centered in the RPMs band.



This means your Prius is quite robust off the line, even though its high speed power is limited.
(This is also why Toyota does not just add the Motor's HP to the Engine's HP to get a total, they make power in different bands)

 

Actually, they don't add the motor HP to anything - they add the battery horsepower to the engine HP to get the total. The motor HP is higher than what the battery can supply because much of the time, part of the engine's power output is being split between the electrical and mechanical paths through the transmission: one motor converts the mechanical energy to electrical energy, sends it to the other motor, which converts it back to mechanical energy. The only way to get power in addition to what the engine is supplying is for the battery to provide it. Hence, the motors are 80 horsepower, the battery is 36 horsepower, and the engine is 98 horsepower. Total system output is 36+98 = 134 horses.