I'm finally getting to work on this pair of '01 H6 OBWs, both acquired over the last year.  Today I got under one to bolt up the junkyard trailer hitch I snagged last weekend, and noticed this weird growth on the muffler - a pair of tubes welded to the body of the muffler go in/out of this little bulbous thing.  Never seen one before.  What is it?

 

the H6es have a hi-flow bypass. Promoted as doing a coupla things, reducing noise but 'perhaps' maintaining scavenging at low rpms, then, allowing higher flow , with more noise, at highway speeds. Noisier at highway speeds anyway so - why not.

makes for a very pricey replacement, many folks at this point in the models' life have just replaced it with some 'normal' aftermarket. Mine is still original but, no rust down here.

Edited May 24, 20205 yr by 1 Lucky Texan

Interesting.  I'm not anxious enough to understand this to cut up a perfectly good muffler, but I"m curious how it works.  Is it just a clever fluid dynamics thing, or is there something in there like a flapper valve that diverts to the bypass at higher flow rates?

 

there is a spring-loaded valve. appears to be pretty 'dumb'/just mechanical.

 

some info/pics here too; https://www.subaruoutback.org/threads/ez-exhaust-mod-anyone-try-it.139/page-2

https://www.subaruoutback.org/threads/header-install.27380/page-2

 

Edited May 26, 20205 yr by 1 Lucky Texan