This is a 12 gauge, CNC laser-cut stainless steel block-off plate for the Series 4/5, (1986-1991)13B NA (non-turbo) Air Control Valve (ACV), located on the lower intake manifold. Use a stock ACV gasket and/or silicone gasket material underneath for a positive seal.This also fits the 1983-5 12A. As with any product that defeats an emissions device, it is intended for off road use only!