Flowmaster Flowfx sound on 340

I'm ready to find some stock mufflers, flowmaster, dynamax, pipes to the tail, doesn't matter. The drone in my 418 Dart at 55mph (3.55's) will deafen you till it hurts. My other Dart , stock 318, (3.55's), with dual dynmax is OK at 55mph, but at 40 mph, forget about it. Definitely going to a stock mufflers with it.
Has anyone tried the 180° pipe on the tail pipe with a cap ?