I know nothing about headers but I do know I would like to quiet mine down. I run a 4.3L Chevy in an experiemental airplane at about 3500 RPM constantly and could use some quiet time. I see Jegs has something called Vortex inset cones and Summit has Car Chemistry inserts that go in the headers. Can anyone tell me if either of these work, what I can expect in noise reduction if so, power loss, etc. Also, the Car Chemistry type show 2 and 3 disc type. Where do these inserts go; in the exhaust pipe ends? Your advice will be appreciated.

 

I saw those, also. You should call Jegs or Summit and get some tech info and post it here for us.