My '64Dog has 2 1/2" Super Turbos 17748 or 9s (I can never remember which) running from the stock Poly manifolds out in front of the rear tires.
"Weedburners"
I have received several compliments from strangers who said it had "just the right sound". The pipes are probably too big for the 318 but I like'em that way.
If I do it again I'll extend pipes to the rear bumper to cut noise a little on those 600 mile trips.

R.

PS: Thanks for the measured data, it is worth much more than the butt dyno.