Thanks for the inputs.
I made an error in my description of the larger header. The ported GMC head single ports have an area equilalent to that of a 1.75 OD tube which I used. But to get equal flow I transitioned the single tubes down to 1 5/8 OD. The ported head has siamese ports areas are equivalent to a 2 1/8 OD tube but I transitioned up to a 2 1/4 OD to get 2x the area of the 1 5/8 single tubes as they enter the collector.
The the tubes are all 36 inches in length. The collector is about 12 inches long.
As for the volume of gas moving thru the pipes, I figure the siamese tubes carry 2 cylinders worth of exhaust and the single pipes only one cylinder at any engine speed. I was trying to get the flow rates equal when the tubes merge together in the 4 into 1 collector. My thought was this would give a smooth merging of gas flow and less turbulance inside the collector.
