So does it not seem feasible that a system that looks just like the stock manifold but bigger pipes would show a small gain....for $350???? Nine dollars less than this??
Look at how each pipe is point straight down the collector when they merge. There is a big reason they are made that way. Compare that to your design.
What carb adjusments did you have to make?
That design shows more promise than the one at the beginning of this thread.....if you sized/shaped the pipes correctly and get the price way down.