mike g, are u using a stock exshaust manifold or a after-market type? the spacer is alluminum on the exterior, the outter shell, and the inner phenolic. the four hole themself's is just plastic, the rest alluminum. here's the site,,. www.spectreperformance.com the part number is, #5764. check it out all. and let me know. if i should use it or not . thanks.