Which blow-off valves will the ‘Whistling Trumpet’ work on?

The optional whistling trumpet works on the Stealth FX, Deceptor Pro and the updated model WRX Hybrid (not the old model WRX Hybrid or the 1003 Hybrid 'universal'). For the whistling trumpet to be effective, the BOV must be set to full vent-to-atmosphere, and boost must be at least 12 psi (0.81 bar).

The whistling trumpet does not work on any other blow-off valves due to their different airflow characteristics.

What does the ‘Whistling Trumpet’ sound like?

In normal driving conditions it gives a typical “whoosh” sound, but once the revs and boost level rise, a high pitch whistle noise takes over.