Warren - Nice pun.
The first header was a 4 into 1 with 1 5/8" and 2" pipes (to match the ports) 36 in long and a 3" collector 12 in long. I bought the tubing from Doug Robinson, (a Land Speed record holder) and he thought 2" pipes were too large. It ran well but 1 7/8" pipes might have been better as Doug suggested.
At the time, I thought the opposite knowing that twice a much gas is flowing out the middle ports. I made a second 1 into 4 header to match a newly ported head and to equalize flow rates. It had 1 3/4" and 2 1/4" pipes. The engine and ported head developed little power below 2000 rpm. I learned the hard way that big pipes do not work and equalizing average flow rates is not the answer. I now see that exhaust pulses are short, separated and flow at high speed. Two cylinders can be serviced by the same size or a slightly larger pipe compared to a single cylinder.
When the smaller header was put on the ported head the car's performance improved quite a bit even though the pipes were smaller than the enlarged ports. In fact the car turned the best time and speed ever: 15.87 sec and 88.68 mph with 3400 lb 40 Chevy Coupe.
Now I am running a dual exhaust system with each header having 1 1/2" and 1 5/8" pipes flowing into 1 3/4 pipes. Total length is 17 inches. 12 inch extensions are added for racing. The best I have done with this combination is 16.018 sec and 84.1 mph. This is slower due to :the driver is getting older, car has been on the road for 23 years, 11 years of racing at LA's Antique National Drags wears things out, and I may have reduced the smaller pipes by 1/8 or so too much. I went to dual headers because the 4 into 1 type has a lot of exposed pipe and they get very hot. I also like the sound of the duals. I am running Jaguar XJ6 1 3/4 exhaust pipe and Jaguar mufflers driving on the road.
I am now planning to build a Tri Y header. I am thinking about two sets of 1 5/8 and 1 3/4 primary pipes 10 inches long combining them into two 1 7/8 secondary pipes about 20 inches long. The secondaries would combine into a 2 1/2" collector pipe about 6 inches long and flowing into some sort of extension or megaphone. What do you think?
