 The naturally aspirated 16-valve version of the 2.0 L— —cast-iron-block engine is the successor to the OHC-engines and a predecessor to the 16-valve Ecotec-line of engines.The 20XE (or C20XE with catalyst) evolved into the X20XEV(1994) with and taking on the GM Ecotec name and finally it evolved into the X20XER(1999).This lineup features the same block as the OHC based engines with an bore & stroke and a Cosworth-developed timing belt-driven double overhead camshaft (DOHC) 16 valve cylinder head (Cosworth Project KB).