Ji'ang is right on the relationship between horsepower and RPM. Like Honda's VTEC engine, it can rev to very high RPM like 8000-9000 RPM to get the peak horsepower, but the torque's peak comes at 6000-6500 RPM. At lower RPM, smaller engine has less horsepower and torque to dirve the car until you rev to higher RPM. So if you want to have a better acceleration, get a V6 or rev to high RPM then gear.