[jambo]

Some of the road legal cans by companies like Remus don't use wadding they use solid metal baffles in their road legal cans. However that makes them pretty heavy.

There was a brief fad for active noise cancellation from one of the companies, Micron IIRC. There was a device on the can that supposedly produced it's own pulses to cancel out the ones from the engine. This still used packing I think, but the idea was to allow legal noise limits with race-can flow.

The fact we're not able to buy them at present suggests they weren't terribly effective.

Jambo