Duke's right - it's pure Silicon metal, not SiO2 that stands proud from the etched bore surface. At higher mag Silicon has a coca-cola color to it. This is a great wear surface with the relief areas acting as mini-reservoirs to hold the necessary oil for lubrication.

The drawback is that compared with cast iron, this alloy is a ***** to machine. It dulls tools in no time. For this and other reasons, I'm personally not a big fan of aluminum blocks and prefer cast iron for mass-produced vehicles.

Peter, the surface is not necessarily porous, except for some microporosity.

Vega's demise of the aluminum block back in 1975 was warpage. The block was otherwise a fine piece of metallurgy.

Steve - it's hypereutectic, not hypoeutectic.

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95 E320 Cabriolet, 169K