It was kinda a Joke, they are 4 inch 19.5 inchs long merge with 2 1/8 primary in. Mr. P helped me with header design and I would have never thought they needed to be that long, but that what the program said. The headers will be 2 step 2 inch 19.6 inchs long to 2 1/8 19.6 inchs long. It will make about a 60 inch long header should pull the gasses well.