At its very basic, the turbo system channels exhaust gas via an exhaust manifold to the turbine side of the turbocharger. When the turbocharger is mounted directly to or very near the exhaust manifold, the manifold must be sufficiently thick and strong to withstand not only the heat of the turbo system, but also the reduction in temperature when the system is not under load or the engine is turned off. Thick cast-iron manifolds traditionally do the best job at this, because they resist warping.
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