for my info I don’t use a pipe because like you said it varies with size so why bother. It does make your flow numbers look better. I know I’ve said it 100 times but honestly I really don’t care about percentages or flow numbers on the exhaust side. I want to see 325 plus FPS airspeed, be a nice quiet port, and I know it will work. Piston travel is helping so if it’s fast and shaped right, it will work.