Complex sentence: Muscle cars come with powerful engines with linear torque and horsepower curves, resulting in better acceleration and top speed, while tuners, because of their small engines, have sharper torque curves--especially when they have turbo-chargers installed.
Split into simpler sentences: Muscle cars come with powerful engines with linear torque and horsepower curves, resulting the better acceleration and top speed. While tuners, because of their small engines, have sharper torque curves especially when they have turbo-chargers installed.