The factory 401 has a 4.165-inch bore and a 3.68 stroke. Doing the math, you get 406 inches at 0.030-over, 408 inches at 0.040-over, and 412-inches at 0.060-over bore. Since we want to make the most power possible, we also want to build the largest engine possible. Not to say that the 406 isn’t a great engine, but we’ve already built a few and we know that they make between 450-500 horsepower with stock iron heads. We want 550-600 hp on pump gas and 800 plus with nitrous to keep up with those turbo Mustangs so we are going to have to increase the stroke if we want maximum horsepower. Stay tuned.