Here is a high performance exhaust manifolds that GM never produced. We have designed and produced what everybody was asking for; true dual exhaust cast iron manifold. This is the performance solution instead of headers. Features: Large 2 1/4" outlet on the driver and passenger side manifolds (original stock manifolds are 2"). The crossover pipe is eliminated from the passenger side. The inner port design is larger with center divider for better air flow. Direct bolt on with no modifications. They will fit 1964 to 1988 small block Oldsmobile egines (307, 330, 350, 403). Will fit all GM A body cars, G body cars, F body Trans Am with a 403, and 1971 and newer B and C body cars.