So below are the headers Mr P speced for me. I am having a problem with collector size. 3.5 inch small side easy to get exhaust adapters for, 4 inch big side and cant find any adapters ie neck downs to exhaust mufflers 3.5 inch, any advice on which to go with.



3 step
1st pri dia 1.986 ... length 18.2 to 19.6
2nd pri dia 2.111 ... length 9.1 to 9.8
3rd pri dia 2.236 ... length 9.1 to 9.8
same collector ... stay on the larger end of spec
all dimensions of tubing are OD with a wall thickness
of .062
collector dia 3.616 to 3.866