Select from 7 Motorsports Systems based upon you choice of Performance. Very Mild Performance, fuel economy, maximum torque, peak torque at lower RPM Mild Performance, trailer towing, RV, street and off-road 4x4, maximum torque, low to moderate RPM Strong Performance, moderate street/strip, hot 4x4, torque and RPM, mid to moderate RPM Serious Performance, street/strip, mid-range torque plus upper RPM horsepower (2 Motorsports Systems) Radical Performance street/strip, pro/street, ET brackets, mid-range, strong upper RPM horsepower (2 Motorsports Systems)