Practical Experience with Passenger Car Engine Blocks Produced in High Quality Compacted Graphite Iron

Although the superior properties of compacted graphite iron (CGI) are well known, its application to the series production of complex castings such as passenger car engine blocks has been precluded by the absence of a reliable foundry production technique. Despite the narrow chemistry range over which high quality CGI is stable, recent advances in cast iron foundry process control technology now serve as the starting point for a comprehensive CGI engine development programme at Adam Opel AG.

The Opel CGI programme originated with the 2.5 litre V-6 DTM racing engine which now delivers 2.7 times more power and weighs 20% less than the standard grey iron production. Acoustical evaluations where then performed on identically designed 2.0 litre Family II engines to show that the audible noise level of the CGI engine was 1.1 to 1.5 dB(A) less than that of the grey iron engine. Simultaneously the 35% higher elastic modulus of CGI relative to conventional grey iron resulted in a 7% increase of the torsional vibration frequency. Other benefits realised from the CGI studies include a 70% reduction in bore distortion, 44% improvement in honed surface roughness (Ra) and more than 40% improvement in cylinder bore wear resistance. As a result of these positive results Opel has recently undertaken a complete redesign of its 1.4/1.6 litre Family I gasoline engine block for series production. The new CGI block is 29.4% lighter than its grey iron predecessor while providing the same power output (105 hp). The purpose of this paper is to present the results of the compacted graphite iron engine development programmes at Adam Opel AG.