duels on stock 225

Dutra Duals are still a thing, yes—a very, very good thing. Pipe size and muffler: Yep, pick 'em carefully; loud exhaust is fun for a couple days, then it gets old in a hurry.

I like 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 (or get this unflanged one. 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.)