i too plan to wrap my downpipe, but i purchased COOL IT's Thermo Tec Exhaust Insulating Wrap (but i would not personally use such a product on headers or the exhaust manifold, nor would i wrap my turbo. my reasoning is the fact that these parts can get so hot they will actually glow. if some of the heat within the pipe was not escaping through it, i can only imagine how much hotter the exhaust would be.
turbo cooling has been addressed in Saab engines through the use of engine oil and water, but dont forget that a huge amount of heat is also disippated through the metal to the air. a turbo that is wrapped can only be that much hotter inside and will take that much longer to cool off.
on the other hand, i see absolutely no issue with wrapping the downpipe, as by the time the exhaust has reached this point, it has generally cooled enough that it will no longer cause the pipes to glow.
also, wrapping the intake pipes is certainly a good idea, as a cooler air charge will produce more power and less risk of engine damage due to knock/detonation. i have wrapped the turbo to intercooler piping in an aluminum-backed cloth insulation. i had noticed how hot this pipe gets due to its location directly behind the radiator (too hot to touch at times) and since wrapping the pipe, and sticking my finger in between the layers of wrap to touch the metal after some 'spirited' driving midday. the intake pipe was not uncomfortably hot, though the air being moved by the cooling fans certainly was.
P.S. most header wrap packing will include a disclaimer stating something along the lines of 'use of this header wrap will void all header warranties'. i cannot recommend use on the exhaust manifold nor any type of turbo wrap.
