Replaces stock, plastic manifold. Must have for big bore engines. Includes new rubber seal. High-Flow, adds 3-5 hp. Easy to install. AVVISO: For closed course competition use only. Not intended for street use. Legal in CA only for racing vehicles which may never be used, or registered or licensed for use, upon a highway. Not legal for sale or use nationwide on any federal pollution controlled motor vehicle under the clean air act..