What you're describing is not a true turbo muffler. It may be a turbo muffler by name only.
A "true" turbo muffler is a straight thru design, as reducing backpressure to as close to zero as possible in a turbo car is the ultimate goal.
I believe a true turbo muffler would be too loud for a car that does not have a turbo in the exhaust path, which helps to quiet the exhaust a little. That is why a lot of people use chambered mufflers on V8's.
I haven't seen a "true" turbo. But now I understand what you are talking about. What I said about a turbo muffler having an S-shaped exhaust path, as in the image below is a true statement. What you said about a "true turbo", straight through design is also true. We are just talking about different animals with the same name. Thanks for educating me as I learn more about exhaust systems.
"Turbo" mufflers may not be what you think they are; the name itself is somewhat deceptive, being more of a nickname derived from the design's original application than a descriptor of its construction. Call them what you want to -- turbo, glasspack or cherry bomb -- but no matter what they're called, you're talking about a design whose performance and signature sound have made it an enduring presence for longer than many hot-rodders have been alive.
The "Real" Turbo Muffler
Manufacturers can call their mufflers anything they want to -- Turbo, Cherry Bomb, Ultimate Titanium Reverse-Flow Carbuncle -- but the term "turbo muffler" actually hearkens back to the 1962 to 1969 Chevrolet Corsair. Chevy's "unsafe at any speed" sports car had a very unusual drive train layout: rear-engine, rear-drive and a horizontally opposed -- or "boxer" -- six-cylinder engine equipped with a turbocharger. This unusual package made for odd packaging, and Chevy had to engineer a very simple, straight-through muffler to fit into the confines of the Corsair's engine bay. This style of "turbo" -- shorthand for "turbocharged" Corvair -- muffler proved a very popular retrofit with muscle car enthusiasts, who loved it for its compact dimensions and excellent flow.
Turbo mufflers typically use a set of perforated tubes, which often guide the exhaust gasses through the muffler in an S-shaped pattern. Although this design is more restrictive than other styles, the S-design allows the gasses to travel through more tubing for better noise reduction. Ideal for street applications, some turbo-style mufflers also incorporate a sound deadening material, which is packed around the tubes for increased muffling.