manifold on left is off of a 1983 engine and allows for bolt up of oil vapors/liquid separation with liquid being returned to oil pan. Manifold on right shows 1980 manifold without liquid return. Also, manifold on the left has a butterfly that is operated by the mechanical throttle linkage. I'm not too sure what the butterfly is in there for. There are no butterflys in the intake of my 300D.

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Jim