We race a number of Small block Mopars.
Even our Superstock 340 Duster was definitely quicker
with 1 3/4 Hooker Headers than any 1 7/8
Header we tried and we tried a lot (The TTI Step 1 5/8 to 1 3/4
is faster yet in our applications particularly with correct stepped collector)
It was one of the First A body Superstock cars in the 9's (Especially
in SSKA @ 3400 lbs).
Of course for the last 30 years we have gone to Proprietary Multiple
Steps headers which a quite a bit faster than any single tube size pipe
header. We guard the specs on these and collectors pretty closely.
If you get to a Division or National Race try to get a peek at the headers
on any cars with similar engine family to yours (If you can without getting attacked).