c.i. are little less then my 449. Ryan used the 1 7/8" into 2" Step header with 3.5" collector, i have not try any other size yet, will be cool to find extra hp/trq.i want to try a3 step w/2 inch to 2 1/8 to 2 1/4 with a 4 inch merge colector, just don't know how tight is going to be on my 65...