My S4 has a Stasis ECU and Exhaust upgrade. Poor Alaskan roads do not spare cars with lowered suspensions. The upggrade vastly improved throttle response and acceleration. the exhaust note is appropriate for a car with a heart for performance. It sounds throaty with quality and appeal. No rattles or annoying cruising droan. With Stasis upgrades, I'm happy to have a four year/50,000 mile warranty, improved drivability, unchanged fuel economy and unbelievable performance. Oh, the price is a bargain!