Got to be careful-- I done dumped a completed essay once already tonight!
I say that the "twice pipe" sound may still be there, because the two pipes have probably been separated long enough to preserve the "growl". Much like an pre-smog MGB four banger, with its two outlet exhaust manifold and twin pipes separated perhaps for some 2 feet. Take off one of its two inline mufflers so you can hear it, and you'll hear a downright nice sounding growl similar to our much loved Raaap. Old '70's era 510 Datsun four banger sedans had a two outlet exhaust manifold with twin pipes separated for only six inches or so, with a loud muffler, just a single exhaust '54 Chevy with a glasspack, sound (or a turbo Cummins with a loud muffler sound-blah!). Separate the Datsun pipes for a coupla more feet, and wait fer th' tickets!
Anybody heard an OHC Pontiac four barrel carb six--they had a very swoopy, double outlet cast iron exhaust manifold with its pipes separated for 12" to 18"--cant say as I never heard one with a performance(loud) muffler, so I cant pinpoint at what length this phenomenon occurs.
Point being, at some point the two pipes can be combined to be a single exhaust system and still have that "normal" (to us) "twice pipe" sound.
