These manifolds can be used as a stock replacement as well as conversion kits for 1984 thru 1989 Big Twin models to eliminate the cracking and leaking problems associated with the stock "rubber" compliance fittings and manifolds. This is accomplished by mounting the carburetor like stock 1990 and later Big Twins and 1986 to present Evolution Sportsters using rigid style induction tracts. The manifolds are designed to improve induction tract air flow and they change the way a stock carburetor and air cleaner assembly fit. This means that these components may require spacing and/or a slight change in mounting bracket(s). Note: Special S&S manifold seals included, does not work with OEM style manifold seals.