1 7/8 Header Selection

I have over the years test dozens of sets of headers on
our 340 Superstock cars and our 408 and 416 Stroker
A body.
Everything from 1 5/8 to 1 3/4 to 1 7/8 to 2 inch.

Nothing that did not cost $2500/3500 plus and was adjustable
performed as good as the now discontinued 1 3/4 Hooker Super Comps.
They were the header of choice for 20 years in Stock/Superstock until it
became a rich man's sport and they spend insane money on stepped/Merged Collector/
Stainless Steel works of art to pick up a few hundreds (not tenths) of a second.

That kind of money would buy you one heck of a lot more performance spent elsewhere.
Given that you are not running a crazy restricted Class like Stock/Superstock.

I still run them on a couple of our Superstockers today when we run conventional
rectangle ports. Some we port to a W2 shape exhaust port which requires custom
headers. The issue on your engine is the Edelbrock Heads are not really big ports
and flow numbers even when reworked (Similar to our stock/ss heads in flow).
If you had some large more "state of the art" heads and properly modifications
you would certainly be quicker with a 1 7/8 or even 2 inch tube header = Just
not the Edelbrock RPMs. I think the cut off would be around 300 CFM intake flow
where I would go 1 7/8.

I believe you would pick up at least several tenths or even more than that
over you Doug's 1 5/8.

A quite nice set of the 1 3/4 Hookers can be found for $300 to 400.

In my testing back to back (last Year) the Hooker Headers were well over a tenth faster that the TTI
Steps that cost me about a $1000.00 on our Superstocker.

Just my .02 Cents worth = For free
Your Mileage will Vary!