Wrap are not good in climates like the Pacific NW where we have rain.. Any condition where water will hit and soak the wrap will cause corrosion. Welds will fail. I have seen my share of turbine housings that have been wrapped, and most of the time I just toss the housings into the scrap bin.. However, for a race prepped only car, wraps have done well. Provided that there is no rain.. All in all, ceramic coatings by a well known company, Swain, JetCoat.. are cheaper and if the headers and turbine housings are prepped good, you have good results..
Results are less than favorable if one uses used parts vs new stainless and high nickle turbine housings.. It also doesn't warrant one coating just the headers, and not the turbine housing.. It is the turbine housing that we want the concentration of heated energy.
Another side note... Wrapping turbine housings do cut the life-span out of the turbine side sealing rings.. The heat tends to prolong the heat soak. It is minimalized if one had water cooled bearing housing, but that out of the picture in our application.. Heat radiating into the turbine shaft and bearings from the insulated wrap is NOT good and can suck out 50% of the life of your turbocharger..