GFB Whistling Trumpet (only for Stealth FX and WRX Hybrid) 5701

The 5701 can be used in place of the standard trumpet on GFB valves (Part numbers T9003 & T9503), and will make a whistling sound. However, it is necessary to run the valve so that all (or most) of the air vents through the trumpet ? Respons valves will typically not generate the velocity required to whistle when set to 50/50 venting. 5701