CDI Unit Top Performances variable ignition Yamaha Aerox / BW’s after 2004. Most stock CDIs are restricted so the engine cannot rev up as high as it potentially could. If you replace it with an “open” derestricted model, you can improve performance of tuned setups. In addition, the CDI with variable ignition timing will optimize ignition which is no longer static but dynamic and controlled by RPM; in most cases this means that ignition timing is advanced to take better advantage of torque. This open CDI with variable ignition timing will allow your engine to unleash its full potential. Perfect for racing engines.