My 239 flathead is rebuilt but basically stock, I might upgrade carb at some point but for now it is just like it left the factory with the exception of a set of Reds "Fat Fender" Headers. The header outlet is 2" and I'm looking for a nice note, should I be reducing the pipe size down? What mufflers are people running? It will be a full dual system.

 

I have red's long tubes on my 276 flathead, with the 2" outlet. It steps down to 1 1/2 after the 17" mellowtone steel packs, just ahead of the rear axle. Initially I had the mellow tones at the header outlet and no pipes. It was kind of crazy loud. I had the pipes run out the back and now in the cab I hear wind noise more than the exhaust. From the back now it really sounds sweet at idle.
I would probably put on shorter steel packs if I had it to do over. Maybe even straight pipes, the pipes quieted everything that much. Sorry I don't have any audio. I'm in the middle of adding dual carbs. Thought I'd have that done in a day, but now I get to wait for parts.

 

I too have Red's headers so I chose mufflers with a 2" inlet and outlet . As yet I don't know what it's going to sound like going down the road .

 

I'm running Red's with 22" Smithy's and 1-3/4" pipe all the way to the rear. Like BK said, the tailpipes really made a difference.

 

When people are talking about glasspacks, are you meaning an actual muffler or just a "hot dog" style resonator. See link below for examples.

PERFORMANCE UNIVERSAL Mufflers / hot dogs | Products

 

Generically, any straight-thru perforated tube muffler with glass or steel packing around the perf'd tube. The linked "hot dog" mufflers for example.

 

I have always used 1 3/4 pipe all the way back. High performance engines may need larger

 

Sounds like 1 3/4" with hot dogs is the go then. I can get the dogs in 12" or 15" long, heart says 12, head says 15.