What is the Control Valve?
The control valve is a simple butterfly valve that is actuated using the pressure from the vacuum lines. This valve controls the ehxuast efficiency, volume and torque characteristics. Some BMW models have actory valve systems in place.

The factory computer determines the timing for the opening and shutting of the valves.
For instance (335i model):
- Always closed on neutral shift
- Opens at 2000 RPM on 1st shift position
- Opens at 4000 RPM on 2nd shift position
Opening and closing are controlled according to any different parameters
(such as the degree of throttle plate opening)

Factory vacuum lines and settings for closing and opening the valves are used for all 3DDesign exhaust systems as the design of the exhaust has been cleverly developed to allow for expansion of these settings for better performance characteristics.
Since the factory exhaust systems (where applicable) has similar valve systems, the installation is simple and no extra modifications are needed.

3DDesign plans to develop and design exhausts with control valve systems for cars not equipped with valves from the factory.