[wrogers55]

Check the sprint car racing community. They too have been hit hard with sound requirements, some as low as 90 db. And that's on an alcohol burning 850 HP race motor. They solved it but the cars sound more like really fast vacuum cleaners than race cars.

I owned the racing school at Laguna Seca in Ca when sound became a major issue for road courses (track days for Cobra guys). The level for professional racing was lowered to 101 db (including Indy cars) and schools were set at 85 db. Our factory pace cars couldn't meet the 85 db limit at full throttle, but the race cars could. It was disgusting. We finally settled on a system that uses something that looks like the old cherry bomb muffler, but inside is an augur looking thing that spins the charge and there is a noise cancellation effect. It's a commercial product, I just can't recall the name. It worked pretty well, with several Supertrap discs mounted on the end.

Also, if there is a standard position for the sound microphone at your track, you can use that to your advantage. The Cobra produces sound on each side without a cross over and only exposes the dual notes from behind, as the car has passed the microphone and getting farther away, which is the biggest help. You might be surprised if you make something that will aim the tip of the exhaust at the track surface to take a lot of energy out of it before it get in the wild. The other side might not be having much of an impact, depending on the location of the microphone.

But, I think the sprint car guys have pushed the technology lately and really have it down. They use little "suit case" stainless steel boxes at the end of the headers (very Cobra like headers) and that does the trick for them. Borla, as I recall, might be the manufacturer. Good luck, I suspect this will only get worse as time goes on.

Good luck,