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Despite the fact that aluminum blocks have made major inroads into the small-block sector, iron continues to dominate the high-cubic-inch builds. This is primarily due to its strength, durability and cost-effectiveness. One of the main arguments against cast-iron heads is that they are prone to cracking from temperature changes, but this issue has been mitigated by the use of modern alloys and thicker deck surfaces.
A new type of compacted graphite iron (CGI) has been developed for cylinder heads that overcomes some of the issues associated with traditional gray cast iron. The key ingredient in this new material is magnesium, which makes the graphite particles nodular rather than flake-like, thus increasing their tensile and impact strengths. This nodular graphite also has an elongation factor, which allows the material to “flex” some within the bore and help resist the cyclic stress caused by valve spring opening and closing.
US Patent 6,318,330 discloses a cast iron cylinder liner with dual phase graphite morphology, having a pearlitic basic structure and graphite precipitations in both compacted and spheroidal forms. The patented alloy has superior mechanical properties compared to state-of-the-art cast iron.
For example, it has been shown to reduce the typical bore distortion under maximum piston side thrust by up to 27 % and have fatigue strength of more than 230 MPa. It also exhibits a Young’s modulus more than 15 % higher than existing iron liner materials and has a higher toughness and ductility.