T-3 24 Valve Stainless Diesel Exhaust ManifoldStainless Exhaust mainfolds are made with shell molding. Its a super smooth inside and out casting technology that has superior flow over and above the old type 60 grit sand paper like and filling casting that all the other exhaust manifolds are made from. The manifolds have 3 4 inch thick center section [for those of you that like to custom port to your specs]. Thick wall casting to keep heat in and the inside runner sizing is 1. 650 inches all the