In the process of slowly getting my turbo kit installed. I was noticing how the heater core hard-line under the exhaust manifold can't have more than a 1/2" clearance beneath the manifold itself. That can't be beneficial to have all that heat put back into the coolant, so I wondered if anyone has tried wrapping it?
I'm sure any benefit would be fairly minor, but if it's even 1-2 degrees cooler I'll take it for practically no effort.

Something like this:

 

It could work to keep some heat away from the coolant. thermal dynamics always seem to work in the opposite way you'd expect.

The "real" solution is to flip your mixing manifold, weld over the hole, wrap your heater core line around by the top hat, and T it into your new, shorter, radiator hose.

Like so:



If you're too busy/lazy/poor to do something like that, especially because of the aluminum welding required, I'd rather see the rubber part of the hose behind the downpipe wrapped.

 

Not really worth the hassle and maintenance. The main thing you are concerned about from the manifold/turbo is radiative heat transfer. In other words, the manifold and turbo "glow" which is why we wrap everything around it with shiny stuff. Fortunately, that tube is already kind of shiny (silver colored). There isn't much conductive heat transfer in that location because you have good air space between that tube and the manifold/turbo, so adding insulation like firesleeve really won't do much.

All in all, I'd focus heat control efforts elsewhere.