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The spark ignition engine is a prime source of vibration energy. NVH disturbances generated by the engine ultimately reach the customer in the form of objectionable noise or NVH. Exhaust Manifolds are one of the many sources of noise contributors among the engine components. Often, the exhaust manifold is identified as a source of objectionable NVH late in the design and development process. Due to the lack of an upfront NVH analysis tool, a new CAE NVH methodology for evaluating new exhaust manifold designs has been investigated and developed by the Ford Motor Company's V-Engine CAE and Exhaust Manifold Design Sections. This new CAE methodology has been developed to compare the NVH performance of current production exhaust manifolds to new design levels. Mechanical induced radiated shell noise is the predominate cause of objectionable NVH in exhaust manifolds.

An L16 orthogonal array parameter Design of Experiment (DOE) evaluated six design parameters of the mating thread interface between the exhaust manifold outlet flange and jointing stainless steel fastener. The objective of this study was to identify optimal parameters for the redesign the thread interface by ensuring 100% seating of the fastener into the manifold flange (here after referred to as stud seating). Since the current fastener and manifold outlet flange interface threads do not always achieve the design objectives, due in part to a form of abrasive wear, consideration was given to develop a testing strategy that would quantify the amount of remaining thread engagement for a given stud length. This testing strategy ensured that the control parameters considered in this experiment would reveal main effects and interactions between the stud and tapped hole threads thus providing the necessary parameters for the redesign on the joint threads.

This article represents the experiences encountered by Ford Motor Company Product Engineering while trying to define a viable method for reverse engineering an exhaust manifold. The intent of this investigation was to develop a reverse engineering technique that would result in the generation of a CAD math model so that current CAE tools, such as FEA, could be applied to analyze current production exhaust manifold designs which have no CAD data base. Investigation into the various types of reverse engineering tools available lead Product Engineering to investigate an X-ray scan or computed tomography (CT) technique. The article focuses on how this X-ray scan or computed tomography (CT) technique was successfully applied to the development of exhaust manifolds.