I've heard that cutting the exhaust tips at a 45 to the discharge path will let the sound resonate away from the fuselage, thereby reducing cockpit noise. I have not done this so I can't comment on how effective it really is.
Don
I went with the mufflers for my IO-320. It is still loud, so if I were to do it over, I would skip them. Less weight. Easier installation. More space against the lower cowl. Less scat tubing. Less heat under the cowl (the mufflers need cooling air).
Best solution for noise is a good active headset.
A downturn really helps. I built a 4-1 for an airplane which originally had a muffler right at the collector - it was still loud. Ultimately the muffler was replaced with a slash cut downturned tip and that was more effective at cockpit sound reduction (and a LOT lighter).
Although I do like the cabin heat up here in the tundra, coming off the mufflers. Can fly in a T-shirt down in the 20's.
Can the standard Vetterman pipes be cut at an angle close to parallel to the fuse floor to come close to the turn down effect? I'd rather not add weight or parts. Does anyone have experience with this?
I wish they would quit calling our heat exchangers mufflers. They do nothing to (muffle) the exhaust noise.
Eddy