Plastic air intake manifolds are successfully replacing aluminum air intake manifolds in most passenger cars and light trucks. Lower weight, performance and costs are the main reasons behind this trend. Of late, welded manifolds are becoming more popular than the lost core manifolds due to ease of manufacturing, lower costs, design flexibility and parts consolidation. The main disadvantage of welded manifolds is the reduced strength of the weld joint resulting from the fact that the glass fibers do not flow across the weld during the welding process. The Original Equipment Manufacturers (OEM's) specify a minimum burst pressure requirement for air intake manifolds and are continuing to seek higher burst pressure values. General design guidelines and welding processing conditions to improve the burst pressure strength of air intake manifolds are given in this paper.The general shape of a manifold, particularly the plenum, plays an important role in the burst pressure strength of welded manifolds. The advantages and disadvantages of various shapes with respect to burst pressure strength are discussed in this paper. The effect of incorporating ribs and posts is also evaluated. The weld thickness and quality, which play a major role, are also discussed. Numerical simulations using the finite element method were conducted to come to these conclusions.Also, discussed in this paper is how welding variables affect the burst pressure strength (a measure of weld strength of the plastic joint) for a particular weld joint design.