Willy has some good points. I just want to add that finding a good intake and head runner size is not easy. You need to do the math to find a good mixture of Velocity/volume. You can find mathematical formulas to calculate the correct runner size. Usually as volume go's up velocity gos down, and vise versa. This is where experience comes in and may be why one motor makes 410hp but its almost identical twin is struggling to make 310hp. Its all in the details. Velocity vs. volume is something that is very debatable and many people have different opinions.