Do you guys have the lower exhaust manifold crossover from left to right pinched or flattened? It looks prefab or OEM but it's too flat to give free flow. Please check your vehicles if we have the same? That's the advantage of dual exhaust so it doesn't have to cross over.
http://youtu.be/ZPYdNxYgxEA
http://youtu.be/ZPYdNxYgxEA