To add more horsepower and torque, go to "Customize", then tune a car up to level 3 parts. Then, go to "Performance Tune/Dyno". Choose for example, "Drag", then go to "Tune Settings". Go to "ECU" and set it so that from 5 rpm to 9 rpm or whatever is the most the maximum amount of torque you can add. Do the same for "Turbo". Then. go to "Nitrous" and set the duration to 4 seconds. This will add both torque and horsepower to your ride.