Recirculation Valves for the Porsche Cayenne V8 TurboWe recommend servicing your valve every 3 years, or 20,000 miles, whichever comes sooner A pair of piston type turbo recirculation valves for the Porsche Cayenne V8 Turbo. With the known failure of the original design which incorporates a rubber diaphragm, we use an alloy piston operating within a billet alloy body to ensure you get the response and turbo boost just when you demand it.