I had a set of the early ,not stainless steel, 14x7oval with 3.0 inch side inlet with center outlet mounted at the rear bumper on my pump gas Duster I built in 2002/2004. It had a 400 stroker motor that made over 600 HP with a 6 pack set up on it, it was loud at WOT with them on , not bad at light throttle cruise
It was NOT restrictive at all, my car only pickup .02 MPH and .02 ET in the 1/8 mile by removing the complete 3.0 inch system from the fenderwell headers back
I'm sure the gain was the weight, not the flow gains
I would buy several more sets of them if I could but I don't see them available anymore