My education continues.

I keep reading about SSI's. I need a bit of definition here. Is this short form for Stainless Steel Heat Exchanges? And how does that relate to the exhaust manifold?

Can someone just run though the exhaust system for me, and what the ideal "current" upgrade is? My VG E has Stainless Steel Heat Exchanges, but having never had an air-cooled car before, I'm not sure what that means, other than it is a very nice upgrade.

thanks in advance

larry