Turbo blanket

[freebeard]

That's one of the advantages.

I'd like to see a rat rod bobber pickup with a flathead and rear mounted turbos.

[aerohead]

One argument for 'any' R-Factor associated with the 'exhaust system' stems from under-hood intake snorkels, where charge density ( horsepower ) suffers from 'ANY' elevated temperature.
Wrapping the headers, downpipe, turbo, etc., reduces the heat transfer coefficient from the exhaust system to the engine bay, providing the lowest possible ambient air temperature entering the intake tract, hence, greatest horsepower.
There'd also be an extremely small increase in available blow-down gas energy available to the turbine side.
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Perhaps the 'best' reason to do it though has to do with burn protection in the pits, between runs.

[to_achu]

I'm not a fan. I'd imagine they do work to some extent, but they're also a fire risk if you wind up with any sort of oil leak. Usually minor leaks will not result in a fire and you have ample time to fix them, but a blanket can both conceal the leak and absorb enough oil to make it a big problem.