This shape is taken from the world famous Harley XR 750 flat tracker. The intake port floor is raised for increased velocity and flow, allowing for a fuller intake charge. Made of alum. An easy drop in kit but some raised porting at 10:00 and 2:00 near the guide may be required for increased performance (see instructions).  Add a dab of JB weld to hold it securely - align with valve guide and tilt into place.  Two reusable teflon heat insulating gaskets included (more images) (installation instructions).