This exhaust manifold collects combustion gases from the engine cylinders and directs them into the exhaust pipe for routing to the after-treatment system. It is mounted directly to the cylinder head and forms the first sealed connection in the exhaust flow path. A crack or leak at the manifold-to-head joint allows unmetered air into the exhaust stream, which can disrupt backpressure and cause a drop in engine torque or trigger diagnostic fault codes. The original casting matches the thermal expansion characteristics of the cylinder head, maintaining clamping force across the operating temperature range. On reinstallation, clean the mating surfaces and use a new gasket; tighten the fasteners in the sequence and to the torque value specified for the engine.