That's it - I couldn't remember Stillen. But their site link is stale, do they even make it any more?Stillen makes a replacement diffuser that rivets into the belly pan. It's made of polyurethane, so should be more resistant to backing into parking blocks and the like.
Haven't noticed any flutter at high speeds, but they will melt a little, with the stock exhaust at least. I noticed it when I was switching over my exhaust from the stock muffler to the X pipe.That's it - I couldn't remember Stillen. But their site link is stale, do they even make it any more?
The poly ought to be OK for most uses but I'd expect they'd "flutter" and would avoid trying them at the mile events.