Horse power limit with exhaust manifold 318

When I built the 318 in my 69 Dart Swinger I had the exhaust manifolds extrude-honed to increase the flow. This worked well as with street-slicks and 3.55 gears I ran in the low 12's at Union Grove Drag-a-Way. This was back in the 80's so I'm not sure who does Extrude-honing anymore, you might Google it and see.