Assuming that you're using the same diameter pipes, identical mufflers, and a full length exhaust on identical cars with identical engines, which will be louder, single exhaust or dual exhaust? Using dual outlet headers, of course.
Also, which will have a better sound? ( more of a rumble, if possible, less popping, and no fart can/ pissed off bumblebee import sound)

I'm not by any means an exhaust engineer, but the straight-6 in my Land Cruiser has a single 2.5" Flowmaster system and the stock exhaust manifold (maybe headers at some point, but that's up in the air at the time being), and it sounds nice and mean. Likely sound even better when I straight pipe the catalytic converters.

I'm a big Flowmaster fanboy, but I'm told Mac mufflers are pretty good too.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me