Extra quiet exhaust

If you have a big bad motor in your car/truck and you want it to be quiet (really quiet) could you put, say four (two on each of the duels) reverse flow mufflers on it without killing your performance? (given that you have the space needed for fitting them)

Lets say that you had 3 inch pipes and mufflers.

I’m thinking of ways to make a killer sleeper,

With the right mufflers I think this could be done with only 2 of them. Many years ago a friend of mine built a VW Bug (an old one, not a New Beetle) with a 401 Buick Wildcat in it.
The exhaust was comparatively short and he used a pair of quiet mufflers on that one. I’ve been beside it at a traffic light and could not even hear it running at all.

If you have a big bad motor and you put a restrictive exhaust on like the one you describe, you will hamper performance. Of course the easy way around this is to install remote cut outs before the mufflers, so you can have the best of both worlds on demand.

The laws of physics suggest that a quiet and low restriction muffler will be large in size.
Lots of internal volume.
Multiple mufflers in series should fit the bill, each one less restrictive than stock.

and cut outs, but please look for a NARA track for your quater mile shoot outs.

A couple of glasspacks or bullet-style turbo mufflers before a couple of quiet turbo mufflers should make for a super quiet system without being too restrictive. Thrush or Dynomax turbo mufflers are quiet, affordable, and free flowing. A pair of either of those, used in conjunction with a pair of glasspacks, would make a stone-quiet system.