This is a GN1Performance "EGR Block Off Plate with an Engraved Turbo and Gn1 logo on it" for a 1986 or 1987 Buick Grand National, T Type, Turbo T, or GNX 3.8 liter turbo V6. Constructed out of billet aluminum.
EGR Block Off Plate
Thick, heavy duty aluminum block off plate. Cleans up the intake area, reduces unsightly vacuum hoses