Jack,
You were close. It's the magic of heat, not pressure.
The hotter the exhaust gas in the header, the less dense it will be. Thus, improved/better scavenging. (The wrap helps keep the heat in)
I'm sure that's where you were going with this.......:s
At least that's the theory.
Is it practical for a street machine? I don't think there would be any noticable difference. Other than having "the look". That and having the desire to replace the exhause on a frequent basis.
Or I guess if someones exhaust system is looking a bit tired and they want to cover it up for a season? They are only prolonging the envitable to replace it.
Jack,
You're still right. And I need to stop reading this forum while I pretend to watch my children. I'm not doing either very well.
Reduced desensity of exhaust gases i.e. lighter.......requires less effort to expell.........less pressure.........
Back to the kids. My apologies..........