An integrated Exhaust Manifold, or “headifold,” is an exhaust manifold cast into an engine’s cylinder head and cooled by antifreeze. This type of design, where the exhaust manifold is no longer a separate part, is becoming a lot more common in the auto industry (see 2017 Honda Civic Type R). Here’s why.
Source: Gizmodo – Automakers Are Changing To Integrated Exhaust Manifolds Because The Benefits Are Staggering