Fuhrmann engine
Compare the Fuhrmann engine at the top with the one at the bottom. It's a 1500, but indeed it only has two single carburetors because there's just one shared intake channels for the two cylinders on each
side.
Just looking at the blower housing, the genuine Fuhrmann engine looks completely different. It has also been converted to use two electric fuel pumps that can be turned off. But the most important features are
the two intake channels with twin carburetors on each side.
As the ignition distributors on each side indicate, the valves are not actuated by a central camshaft via pushrods, but directly by two overhead camshafts on each side. And these, in turn, by a main shaft on
each side.
You can see it very clearly here. All that remains of the original camshaft in the crankcase is a shaft connected to the driven wheel on the crankshaft. This shaft, just like the former camshaft, is located beneath the
crankshaft. In addition to the bevel gear drive leading to the main shaft shown here, the one on the other side is also visible.
Of the usual four pushrods and their surrounding tubes, only one shaft remains connected to the cylinder head. The situation is further complicated by another set of bevel wheel gears, between the intake and
exhaust camshafts.
Although there remain still two valves per cylinder, they can now be arranged in a much more roof-like configuration, bringing them significantly closer to the hemispherical combustion chamber. A central
spark plug is not possible, but one or two that are located near the exhaust valve.
Thanks to the more favorable combustion chamber, the compression ratio can be increased, initially to 9.0:1 in the Speedster's engine. The overhead camshafts also enable a higher
output of 74 kW (100 hp) at 6,500 rpm.
The engine first appeared in the Speedster in 1957, to which we will pay attention in a separate chapter. Starting in 1958, it was available in the Convertible model with a compression ratio of 9.5:1, producing 77
kW (105 hp) at 6,500 rpm and 121 instead of 117 Nm at 5,000 rpm instead of 5,200 rpm.
By 1959, the engine displacement had been reduced to just 1,600 cm3, with the Fuhrmann engine, now featuring a compression ratio of 9.8:1, delivering 85 kW (115 hp) at the same rated speed
and 126 Nm at 5,500 rpm. The Roadster reached a top speed of 185 km/h.
In the end, the speedometer had to be calibrated up to 250 km/h because the engine displacement increased to 2 liters, allowing the car to reach 200 km/h with 96 kW (130 hp) at 6,200 rpm. The torque was
now 162 Nm again at a very civil 4,600 rpm. That was the final result for the fastest road-driving 356.
The 901 and 911, which came on the market at the same time in 1963, also did not have higher horsepower. Originally, the distributors were located at the ends of a camshaft on each side (top image), but
were then moved together to the end of the crankshaft with the appropriate gear ratio (bottom image).
The dual ignition system was also widely adopted later on; it was not only more reliable in terms of preventing failure but also allowed for control of the ignition in the combustion chambers. In general, the
engine was very dependent on a good setting, actually quite sensitive.
This was relatively harmless when it came to the valves, but it also affected the assessment of the bevel gear pairings with regard to noise, overheating and tooth flank corrosion. The axial
preload also played a major role in this valve train.
The worst part of the whole situation was that damage to the camshaft bearings, gears, and especially the valves led directly to a complete engine failure. This included, for example, a broken valve spring or damage to a
rocker arm shaft.
The consequences of incorrect synchronization of the now four instead of two carburetors were not quite so bad. It was estimated that a complete engine adjustment would take 5 to 8 hours. Even just to
change the spark plugs, the engine had to be removed.
Despite Porsche's reinforcements, the crankcase was still based on that of the VW Beetle. It was still considered unsuitable for improving performance even later on. At least the oil cooler was no longer
in the now slimmer blower housing and the system had been converted to dry sump.
| 
