 The last version was called "C20LN" (Low Noise) and has a stronger engine block.In 1991, the "Coscast" cylinder head was replaced with the "GM" cylinder head which was manufactured by Kolben-Schmidt.One of the most prominently recognized qualities of the "Coscast" head is its inherent lack of porosity; this was achieved by pumping the liquid metal into the mold rather than pouring it, hence, minimizing the presence of tiny air bubbles that usually form during the standard casting process.