These are high temp VITON valve stem seals for the BA BF 5.4L 4V Cylinder Heads including FPV GT Boss 290 Heads, Ford GT / Shelby GT500 Cylinder Heads.

These Viton Valve Stem Seals for the Ford Modular 4.6L / 5.4L 4V DOHC Cylinder .
 
High Temp Valve Stem seals
 
These seals are designed as a direct replacement for the OE part but with performance in mind. The OE type seals are recommended for standard OE diameter valve stems only. We use only OE type materials for these seals including Viton©, polyacrylate and nylon. While many competitors use low quality nitrile materials we use only OE material or better. We've got you covered with a full line of seals for your rebuilding requirements.