The exhaust manifolds has a port size of 1.5" and then there is a weld inside that holds the flange on. That weld is almost 1/8" that drops your exhaust gases trying to get out a hole of 1.25". The V8 exhaust manifold isn't much better at 1.75" but the weld is very small. Here are some pictures of my V8 exhaust manifolds after clean up.,,,,,had the hardest time loading pictures.