Exhaust manifolds on turbocharged cars channel potential energy to the turbocharger. Any energy that is lost to either the manifold or ambient air will not reach the turbo. This energy, therefore, cannot be used to spin the turbine wheel and turbo performance will be reduced. This means it will take the turbo longer to reach target boost.

The goal of wrapping and coating manifolds is to keep as much heat, or energy, in the exhaust system as possible. Exhaust wrappings and coatings achieve this by acting as an insulation between the hot manifold and the cool ambient air rushing around the manifold. Stabilizing the temperature of the exhaust gas, with the use of exhaust wrappings or coatings, will improve turbo performance.

Deciding whether to use exhaust wrappings or a coatings is ultimately up to the end user, but generally cast manifolds take better to coating than tubular manifolds, just as tubular manifolds and headers are easier to wrap than cast manifolds since they have a more open design.

One last note on wrapping or coating exhaust manifolds, be sure to check with the manufacturer of your manifold to see if wrapping or coating it will void the warranty as different manufacturers have different policies.