454cid
Sooper Pooper
The stock 3" in/3" out cats on my Express van were actually quite restrictive. When I put the Tri-Ys on the Express I swapped out the cats for Thunderbolt 200 cell count metallic core cats and swapped the magnaflow for a bus muffler. ZERO drone from my 350. Almost all of my engine note is intake growl.
What makes you think it was the cats that were the restriction and not the exhaust manifolds?