I use these on the street. I'v never tested them to see what kind of power they lose.
I saw this one on a car at a show; I didn't get to speak with the owner. But I have heard it's available from TWM.
On the track I use these stacks, But I leave them open. The "Tea Strainers" cost me an honest 100hp, dyno proven.
This diffuser gives me about 8mph at the top end.
