Here are two interesting articles on intake manifold design :
https://horsepowercalculators.net/intake-manifold-design/intake-manifold-design
https://www.custom-car.us/intake/intake-manifold.aspx
https://horsepowercalculators.net/intake-manifold-design/intake-manifold-design
https://www.custom-car.us/intake/intake-manifold.aspx