The Banzai Racing Billet Aluminum Filler Neck is designed to be a direct replacement for the 86-88 FC RX-7 plastic filler neck. This part is used to eliminate the AST (Air Separation Tank) on the 93+ RX7 that have the two piece thermostat housing. The kit comes with a new Viton O-ring and stainless hardware. Uses OEM or aftermarket pressure cap.

Air Separation Tank (AST) (93+ RX-7)

 

Here is a great example of why I designed this product.

 

Awesome!