Tupy revealed cast iron petrol engine with same weight as aluminium at Vienna Motor Symposium. Compacted (Vermicular) Graphite Iron (CGI) has effectively become the standard series production material for heavy-duty cylinder blocks and heads, and for V-type passenger vehicle diesel engine cylinder blocks. However, CGI has not yet established a series production reference in the high volume in-line petrol engine sector that comprises the majority of the global passenger vehicle market.

With CGI series production capability on seven lines, and production of more than 100,000 tonnes per year of CGI cylinder blocks and heads, Tupy initiated a comprehensive development programme to demonstrate the potential benefits of CGI for in-line petrol engine applications. The development culminates with the formal introduction of the engine, at the 2022 Vienna Motor Symposium. Beginning with a series production 1.2 litre three-cylinder engine based on an aluminium cylinder block, Tupy re-imagined and re-designed the cylinder block.

The running surfaces and structural areas were specified in high-strength CGI while the outer enclosures of the cylinder block were uniquely fabricated from low-density high-durability PA66GF30 plastic. The revised engine was simultaneously upgraded to a 48-Volt hybrid configuration to further demonstrate the potential of CGI in small petrol engine hybrid and range-extender applications. The CGI cylinder blocks and ladderframes were produced under full series production conditions at the Tupy foundry in Saltillo, Mexico, incorporating state-of-the-art 2.7 mm nominal thin-wall technology, fracture-split main bearings and an industry-first for CGI: Grade CGI 550, with more than 550 MPa tensile strength.

The introduction of CGI 550 provides at least 1.8 times higher tensile strength, double the stiffness and more than double the fatigue strength of the aluminium used in the original engine. Benefitting from higher strength, the CGI alternative required 54% less metal volume than the original aluminium engine, increasing the crankcase breathing area by a factor 2.25-times. Modal analyses simultaneously showed that the global flexural modes of the CGI 550 block were 5% higher while the main individual bearing caps were 20-40% higher, due to the combined contributions of the material stiffness and the ladderframe design concept.

Ultimately, the CGI alternative provided the same weight as the 48-Volt derivative of the original aluminium cylinder block assembly, finishing at 20.06 kg for CGI and 20.47 kg for aluminium. The outer dimensions of the CGI cylinder block were intentionally maintained the same as the aluminium block, in order to allow components from the original aluminium donor engine to be assembled into the CGI engine for durability testing. The CGI engine successfully passed a 100-hour proof-of-concept durability test including operating periods at full load of 5,000 rpm and 183 Nm, providing parity for weight, performance and power density.

While the carryover of the aluminium engine dimensions enabled the assembly of a running engine, it is estimated that a clean-sheet design approach would have enabled up to 5% of additional weight reduction for the new CGI design concept. Widely studied in previous research, the production of cast iron has significantly lower CO2 emissions than the production of aluminium. In the specific case of passenger vehicle cylinder blocks, even with the favourable assumption of infinite recycling for aluminium, the benefit of cast iron can save 40% to 70% of the manufacturing CO2 emissions compared to aluminium, according to a publication at the 2017 Vienna Motor Symposium by Cranfield University.