Aluminium Hex Head oil Restrictors MI23100Aluminium Hex Head oil RestrictorsSuit SB & BB Chev MI23100 23100 These plugs solve the common high performance engine problem of too much oil in the head area. The plug restricts approximately 75% of the oil to the top end of the engine for better lubrication and prevents oil wastage at the lifters (which will cause windage problems). This also keeps the sump better supplied with oil. Installs easily into the back of the block in place of the stock