Tuned header?
 

I am having trouble finding a header that will work with my brodix track 1 heads. I found THESE but is says they are not "tuned" headers. What does this mean?

I am looking for headers with "D" ports and that will work with angle plugs and these are all that i could find.

I think what they mean when they say tuned headers they refer to the equal length of each tube all the way down to the collector.