/6 Exhaust: Dual or single? Your thoughts
Dutra Duals, better than headers unless you're going racing. 2" pipe off of each of the two exhaust manifolds, into
this wye connector, 2-1/4" pipe from there to
this muffler. It's in Walker's QuietFlow SS premium OE line, all stainless steel (which is nice for durability), made for the '01 Jeep Cherokee 4.0 so it's easily got the flow capacity for a healthy 225 and it's tuned to keep an inline-6's exhaust from droning, has a 2¼" inlet and outlet (can easily step down to a 2" tailpipe). The inlet has a 2-bolt flange meant to bolt directly to the outlet of the Jeep's catalytic converter, but there's plenty of length to the input pipe that the flange can just be sawed off in 5 seconds at the exhaust shop. It's got the 4¼" × 9¾" housing, muffler shell 20" long, so it'll be a bit of a tight fit in an A-body, but it will fit.
2" tailpipe with resonator. If I'm rich, I like a
Flowmaster HP2 stainless unit with 2" in and out. It's 18" long, which is a workable fit behind most A-body quarter panels. If I'm broke, I like a Walker №
17198 4" round can-type unit, 2" in and 2" out, with offset outlet next to a proper hanger bracket.
Speaking of that, whatever muffler you wind up with, make sure to use very soft hangers. The hook-and-O-ring type, for example. Today's popular "rod and rubber box" type transmits a lot of noise to the passenger compartment.
(Tailspout outlet 45° or greater downward.)
I want it to sound nasty.
Loud exhausts tend to be fun for a week, then get old in a hurry. But if you're real sure you're not gonna get tired of it, then Dutra Duals, 2" pipes all the way back with no crosspipe, two of the muffler I link here in this post. It'll be edgy at all RPMs, and when you rev it up it will be very "rappy". Remember, the lower the volume flow through any given muffler, the louder it's going to be. So a muffler with three cylinders' worth of exhaust going through it is going to be louder than that same muffler with six cylinders' worth of exhaust going through it. 2" pipe instead of larger because you want to keep your exhaust velocity up -- not just for flow but for the loud sound you want.
