The reason an I-6 sounds different with a split manifold is that each successive exhaust impulse comes out a different pipe. With a firing order of 1-5-3-6-2-4, the front flange gets the exhaust from 1,3,then 2, and the rear outlet gets the gas from 5,6, and 4, in order. This creates a unique resonance which can only be (kinda) duplicated from a V-8 with a 180-degree firing order, requiring a special camshaft, crankshaft, and distributor setup. Those 180 V-8's were used mainly in sprint cars, etc., and the exhaust note is definitely different, kind of like a 4-cylinder on steroids! The 120-degree separation of a split-manifold 6 has a resonant frequency unlike any other engine. A set of "steelpack" mufflers, with steel wool instead of fiberglass packing added the final tuning to a split manifold setup, and it would rattle windows for half a block!
Jerry
