It's a crank case breather. It's used to equalize the pressure in the head & crankcase on AVCS headed 207's.

The rear one is the one you use for the PCV system as it's has an oil/air seperator under the outlet (inside the rear of the block).

Alternately you can 'T' the rocker cover vents to this & run a single PCV source from the rear outlet.

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[CENTER][COLOR=#ff0000]Built Ej207: Semi-closed RA Cases - Wiseco Forgies - Manley rods - BC 272 cams - GDA Heads - billet f/whl - Vi-pec - WbO2 - 800cc Yellow tops - TD05-20G - 409Hp ath @ 1.75bar on E85[/COLOR][/CENTER]