From its introduction in 1964, the 911 has featured a flat six engine cooled by air. This design, which started at 1,991cc, proved unimaginably adaptable and with Porsche’s ingenuity it doubled in capacity and power over three decades while gaining in economy. However, the march of emissions regulations meant that by the late 1980s, the writing was on the wall for the last remaining production air-cooled engine. It was clear that a four-valves-per-cylinder head would be essential to create the more efficient combustion required to both improve performance and economy, and address looming CO2 reduction targets.
Experience with the 959 had shown that while it was possible to build a multi-valve cylinder head on an air-cooled block, the head would require water-cooling, and the complications of this made series production too expensive for 911s. Porsche, therefore, had little option but to abandon the air-cooled design, though courageously it stayed with the flat six architecture
