The opportunity for composites in engine closure systems such as valve covers, oil pans, and timing belt covers is expanding rapidly. The primary driving forces are lighter weight finished components, integrated designs, improved isolation of engine noise, improved materials systems, and matured manufacturing processes for composite materials. Thermoset-based composite materials, particularly those based on high-temperature resistant epoxy vinyl ester matrices, offer improved performance with respect to thermoplastic and thermoset polyester-based composites and can be manufactured using different processing methods.This paper presents the current state-of-the-art design, engineering and optimization techniques for engine closure systems. The performance requirements of different systems such as valve covers and oil pans are explained in detail. Techniques for long-term structural stiffness evaluation, vibration performance assessment and noise transmission estimation are described. The paper also shows the material characterization required to develop design allowables for long-term, high-temperature composite applications. Definitions of design allowables and examples for thermoset-based composites are also included.COMPOSITE ENGINE CLOSURE SYSTEMS such as valve covers, oil pans and timing chain covers offer several advantages over systems based on traditional materials, including cast aluminum and stamped steel. Composite systems can provide the same design flexibility as cast aluminum at a lower total cost. Unlike stamped steel systems, features such as brackets, bosses, tubes, grooves and lettering may be integrated into the part without additional fabrication or machining. This design flexibility also allows noise emission reduction and parts consolidation opportunities such as providing structural support for other engine compartment components.Since composites typically have half the strength and one-fifth the stiffness of aluminum, the composite closure systems require detailed global and local engineering analyses during the design process to provide acceptable deflections and stresses upon static and dynamic loadings during long-term exposure to under-the-hood conditions. This paper presents techniques and recommendations for designing and optimizing composite engine closure systems.