ALL THE PERFORMANCE WITH THE NOISE! The Hybrid valve is back! In 1999, GFB's first Hybrid valve pioneered the dual port design, which was so successful the technology has since been adopted by most other brands. By "staging" the two venting outlets, at low valve lifts most of the air is recirculated. As the car is driven harder, the valve opens further and more of the atmosphere venting port is exposed for a louder sound. As a benefit, this system makes it possible to use these valves on cars with sensitive airflow meters that often suffer issues such as backfiring and/or stalling, whilst still achieving the signature blow-off sound.