One of the most significant changes ever made to the VW flat four…
The twin-port cylinder head holds a very special place in Volkswagen history. It was first used on a production vehicle in the US-market Type 3 in 1968, and immediately heralded a vast improvement in design. The individual intake ports, one for each cylinder, made it superior in every way and far more efficient than the single ‘siamesed’ one-into-two intake on the heads of all previous VW production engines.
Though it was new to the VW range, the twin-port head could never be classed as new technology in 1968. Franz Xaver Reimspiess, the engineer who, in 1936, came up with the 985cc E60 air-cooled flat four (the basis for the VW production engine) designed the heads with twin inlet ports but, by the time the VW38 prototype series engine went into prodcution in 1938, the cylinder head had reverted to a single inlet port.
The reason for this was the 1131cc production engine was designed to be a frugal, reliable, low-revving engine, so two ports were deemed an extravagance. However, VW owners in search of more power in the 1950s found Gerhard Oettinger’s tuning company, Oettinger Kraftfahrtechnische Spezial Anstalt (Okrasa for short), had exploited the benefits of the twin-port configuration on its TSV heads, selling them as part of their engine tuning kit. Fitting a pair of Okrasa heads, manifolds and twin Solex 32PBIC carbs could wipe 12 seconds off the zero-60 time of your Beetle!
Throughout the 1950s and ’60s, VW continued to see no benefit in a high-performance Beetle, so soldiered on with the single-port head design, on all including the largest engine offered, the 1493cc (1500). Even the 1584cc (1600) Type 3 with its dual carburettor engine had single-port heads, though perversely, the saving grace came in the US National Emissions Standard Act, introduced in 1968.
To comply with this, the 1968 Type 3 model used Bosch’s D-Jetronic fuel injection system, which worked on pulses from the inlet manifold to monitor the correct fuel delivery to each cylinder. Twin-port heads were essential for the Bosch system to work.
As a result, the twin-port head arrived at last. It took until 1971 for the benefit to reach the Beetle range, with the introduction of the new 1302 model. This was 30kg heavier than the previous Beetle and needed more power to haul that extra weight around, while keeping performance at a similar level. To achieve this, VW made slight adjustments to the Type 3 head and fitted it to the 1302 and 1302S models.
Though it was never VW’s plan, the separate inlet port design gave far greater scope for tuning the flat four, and the twin-port head went on to become the foundation for just about every aftermarket performance cylinder head produced to this day.
There’s no doubt the twin-port cylinder head is a VW Icon.