Noise in cabin is acceptable. And I just use passive headset. Is a glass plane. makes big diff from aluminium so hard to compare with others Ive flown as to whether its airframe or engine related.
Original exhaust exited at 90deg to cowl and was quieter than this one but did not flow as well. This time I turned the outlet about 30deg back so can actually see inside of pipe while flying. reckon I get a bit more noise because of this.
Was quick to make but had to do in right sequence to ensure could get full welds everywhere needed. Just used 5mm mild steel for end plates, ms mig wire to weld 1.6mm 304ss pipes to manifold & end plates.
Inner section of original mazda renesis manifold was not welded. Is just slip fit to allow movement.
Now wish I took pic's as we put it together but really did not expect it to work as well as it does.
Just the turbo by itself will tame the exhaust pulses lots on your plane if you use properly sized hot section rather than a wastegate.
Lots of things can be done to reduce noise. On your current setup just tack welding a washer into end of pipe will help lots. Just keep increasing hole size until backpressure is not an issue. About 25-30mm out is all thats needed. If your smart enough you end up with a tuned exhaust. But that is way beyond me.