Beyond the Vega - 50 years of Al-Si engines · Today’s liner-less aluminum engine blocks allow for smaller high output engines with

Beyond the Vega - 50 years of Al-Si engines Today’s liner-less aluminum engine blocks allow for smaller high output engines with reduced weight, tighter bore centers, and larger bore sizes than previously possible with a similarly sized iron sleeved aluminum block. This allows for an increase in displacement and output without the need for increased cooling system capacity.16 Improved thermal conductivity also allows water jacket depths to be reduced 30 to 65%, reducing engine weight and cooling system volume, which improves engine warm-up and reduces emissions.17 The long term durability of aluminum engines has always been a concern for manufacturers. In Porsche’s own testing, cylinder deformation was much lower with Alusil than earlier cast iron cylinders and engine blocks. Extensive testing by Porsche with air-cooled 2.7 and 3.0 engines as well as their water-cooled 944 and 928 engines showed that early Alusil cylinders did not exhibit scoring of cylinder walls or pistons. Although wear was twice as high as cast iron, it was still within acceptable wear limits, and the use of hypereutectic aluminum alloys in the construction of both air-cooled and water-cooled engines allowed engineers to overcome thermal and geometric limitations.18 Alusil hypereutectic (Al-Si) engine blocks are low pressure die cast from hypereutectic aluminum with 17% silicon content. The silicon particles in the bore are exposed through an activation process and the piston skirts are coated with iron or other dissimilar material to prevent aluminum to aluminum contact. This eliminates the need for iron sleeves. Although Chevrolet’s Vega was not successful, it paved the way for later engines based on this technology. For example, with the 944, Porsche was able to get 30% more power and 25% increased displacement over the 924’s cast iron engine it replaced, without any added weight.19 Besides casting blocks in Alusil, all-aluminum liner-less blocks can be manufactured with heterogeneous cast-in hypereutectic aluminum sleeves such as Albond and Silitec, just to name a few. In the case of the Boxster, Porsche’s first production water-cooled horizontally cooled engine was also the first to utilize Kolbenschmidt’s “squeeze-cast” Lokasil I MMC (metal matrix composite) cylinder technology. Asian automakers developed their own liner-less engine blocks using selective reinforcement and MMC cores. Starting in 1990, Honda first introduced a carbon fiber and alumina reinforced aluminum engine block20 with the Prelude Si and later performance models including the NSX and S2000. Toyota’s first all aluminum MMC engine was the 2ZZ-GE which also used preforms with ceramic alumina-silica fibers and mullite particles21 rather than Lokasil’s selective reinforcement with silicon and alumina.22 Pistons are 16 The Boring Truth: Everybody's got ideas about treating cylinder bores; strong ideas. Wards Auto. April 1, 1999. 17 Reconditioning of Aluminum Engine Blocks. MSI Motor Service International. 18 The new Porsche 944 4-cylinder aluminum engine. Paul Hensler. Porsche AG. SAE International. 19 The new Porsche 944 4-cylinder aluminum engine. Paul Hensler. Porsche AG. SAE International. 20 Replacing the Cast Iron Liners for Aluminum Engine Cylinder Blocks: A Comparative Assessment of Potential Candidates. John Lenny Jr. 21 MMC All Aluminum Cylinder Block for High Power SI Engines. Toshihiro Takami, et al. Toyota Motor Corp & Toyota Central Research and Development Labs, Inc. SAE Technical Paper Series 2000-01-1231. LN Engineering Technical Library. Copyright ©2019 LN Engineering LLC