I agree. Maybe I,ll try to modify my smaller 4 into 1 header. It has 1 5/8 & 2 inch header tube 36 inches long and a 3 inch collector.
I will start by enlarging the flange ports and flair the 90 degree bends to match the larger head port sizes.
This still doesen't cure the difference in gas velocity entering the collector. The siamese tubes carry 2x the volume of gas but are only 1.6 times area of the single tubes so velocity has to be 1.3 faster.
