Check this out I was trying to figure out how much a difference in flow it might make going from the stupid 2" reducers and smashed downtubes on my shorty headers to 2 1/4" all the way through.
"Science be praised" lol
Pipe Diameter (inches) Pipe Area (in2) Total CFM (est.) Max HP Per Pipe Max HP For A Dual Pipe System 1 1/2 1.48 171 78 155 1 5/8 1.77 203 92 185 1 3/4 2.07 239 108 217 2 2.76 318 144 289 2 1/4 3.55 408 185 371 2 1/2 4.43 509 232 463 2 3/4 5.41 622 283 566 3 6.49 747 339 679 3 1/4 7.67 882 401 802 3 1/2 8.95 1029 468 935