Unfortunatley,cast iron manifolds may not offer as good of flow as tube headers,but the fact is that they retain heat better, which actually makes them better for turbo use.Another problem with tube headers( they get red hot with a turbo)is they do not support the weight of the turbo as well, so they are prone to bend, leak and crack. Having a good flowing exhaust system after the exhaust leaves the turbo is more benifical.Paul
