Exhaust manifolds, or exhaust ports, were components of starships responsible for venting plasma from the vessel's propulsion systems into space. Exhaust manifolds could often get clogged with EM residue, and required periodic purging. Vectored exhaust ports, as those installed on the Delta Flyer II, lent themselves to increased speed and maneuverability. (VOY: "Drive") In 2152, upon discovering a a vessel from the 31st century, initial scans indicated no signs of any plasma exhaust ports, leaving the Enterprise crew confused as to the vessel's method of propulsion. (ENT: "Future Tense")