Because since 1980 I have been throwing away 1.625 headers on everything and going bigger. Have done so many dyno tests to prove the dumb small tube header thing it's now senseless.
Like I said...there is a current (last 90 days) magazine article with 1.875 heads that made big power. There is a TV show that dyno'd a 302 FORD that pick up 15-20 HP and about the same on TQ going from 1.625 to 1.75 headers. On a 302 FORD.