I'll check with GMG next week but has anyone ever used spiral or auger muffler inserts to reduce sound? I just received my new to me 6TT (GMG 3.8 WC) and peeked into the exhaust tips and sew these inn both sides. I'm sure they are restrictive but not sure how much power they rob. Anyone have an idea?

 

I've not used those on my 996, but I have used and seen them on other cars to meet sound regs.. The theory is that because it guides the air in a spiral it reduces turbulence/backpressure compared to a traditional baffled muffler. I didn't notice a difference in power, but the car with my experience was also not anywhere near the power output of a modded 996TT.