 911 - Part 1
It is said that, at the very beginning, virtually nothing was clear about the development of the 911. So let’s start with the only constant: the fact that the engine for the new car is likely to have six cylinders.
Although there were several prototypes with four-cylinder engines, the new number of cylinders had been finalized.
That makes sense, since the four-cylinder engine already had a displacement of two liters. At the time, it was apparently still assumed that this could not be significantly increased. Later, things turned out
differently with inline engines. Suddenly, Porsche had a four-cylinder engine with a displacement of three liters.
After all, the new six-cylinder engine eventually surpassed that record as well, but let's take it one step at a time. The rest of the development history of this engine alone is actually quite interesting. It’s
important to note that the old model required a truly ingenious design to accommodate four camshafts in the cylinder heads.
That is why a bumper motor was initially under consideration. But that also meant a second constant: the decision to stick with the boxer engine. As a rear-engine vehicle, its compact design kept it relatively
close to the rear axle, resulting in minimal overhang and a rearward shift in the center of gravity. And speaking of the center of gravity, it was also particularly low thanks to the engine’s exceptionally flat design.
With cylinders divided into two groups, an inline engine naturally requires four camshafts at the top instead of two, whereas a bottom-mounted design can be made much simpler. In the case of these engines
from VW and Porsche, there is the added benefit that only half the number of cams is required, because each cam serves both sides at an angle of 180°.
However, in that case, only one camshaft is responsible for both the intake and exhaust valves. It remains unclear whether they were far-sighted enough back then to anticipate that these would someday be
adjusted differently. The fact is, however, that there was a design with one camshaft above and one below the crankshaft. It is highly likely that one was responsible for the inlet side and the other for the outlet
side.
As you might have guessed, nothing came of that plan. Lower-mounted camshafts unnecessarily increase the mass that must be accelerated back by the valve spring, especially if a hydraulic tappet is added
at some point. In the case of overhead camshafts with rocker arms, the design can be such that the rocker arm is no longer considered part of the moving masses. The exhaust valves are sodium-cooled.
While it is indeed possible to have four valves per cylinder (e.g., in trucks), this does little to simplify the issue of weight. Historically, OHV engines have only been expected to operate at speeds of up to about
7,000 rpm. You can probably guess that a limit crept in here as well, one that was far from sufficient for any future plans to compete in races.
All in all, it probably didn't take very long for things to become clear. However, there was only one camshaft per cylinder head, which actuated the two V-shaped valves via rocker arms. If you take the timing into
account, it should actually be clear which connection to the crankshaft was chosen. The complexity of two crankshafts was still clearly evident in the example of the Fuhrmann four-cylinder engine.
But the timing belt was also still in its early stages of development. Well, Glas had already implemented it in the 1004 back in 1962, but the company was also known for taking significantly greater risks than
Porsche could afford, given its much higher retail prices. What remained was the good old tried-and-true timing chain, albeit now combined with hydraulic chain tensioning.
| The exhaust valves are sodium-cooled. |
However, the design of the crankshaft was much more forward-thinking than that of the camshaft. When has there ever been a boxer engine with one more main bearing than the number of cylinders? Sure, in
the VW Boxer engine they're listed as 'four', but that includes one that's completely irrelevant to the actual crankshaft mechanism.
Perhaps that was also why the engine was so long, something Ferry Porsche lamented when he saw just how much it could still be bored out. No, it was a good thing not to make it any more compact. And to
give the crankshaft that kind of stability anyway. It is said that the crankcase was originally made of aluminum and that magnesium was added only later.
It’s important to note that the Beetle’s engine has always had this type of housing and has always suffered somewhat from the relative instability of its engine block. After all, the models built up to and
including Type 3 should really have been capable of producing more than 40 kW (54 hp) from a 1,600 cc engine, if one adds the corresponding Porsche engines. However, one did not dare to believe this, and
for good reason.
And while we're on the subject of performance enhancement, which is so important to Porsche. The VW engine was also very sensitive to even slight increases in temperature. Here’s a memory of my
workshop foreman, who had dared to perform a rather harmless tune-up and then, as a thank-you, was constantly tinkering with new ways to provide the engine with better cooling.
Porsche seems to have realized this early on. Even the earliest models had an oil circuit that included an oil filter. So it seemed perfectly logical to equip the 911’s engine with a dry-sump lubrication system,
which, incidentally, started out at a modest 9 liters at the time. Later on, the series reportedly reached up to 20 liters, and in some cases even more.
The basic idea was that if the engine still got too hot, you'd just make the reservoir a little bigger. However, it was important to keep in mind that this amount also needs to be warmed up by driving. It remains
to be investigated whether, as with the oil cooler, there were any thermostatically controlled options for adding coolant when necessary.
BMW has already referred to certain motorcycle engines as 'air-cooled' or 'liquid-cooled'. In other words, oil played an increasingly important role. But Porsche has also been making full use of air cooling for a
long time. The cylinder heads have always had more cooling fins than those made from other manufacturers. In addition, even though some of them had an oval double channel, they were large enough that the
cylinders just fit side by side.
Speaking of air cooling brings us to a characteristic feature of all 911 engines, at least until they became liquid-cooled, namely the blower with a directly downstream generator, essentially a relic of the good
old Beetle engine.Speaking of air cooling brings us to a characteristic feature of all 911 engines, at least until they became liquid-cooled, namely the blower with a directly downstream generator, essentially a
relic of the good old Beetle engine. In that case, the alternator warning light would come on if there was a risk that the V-belt had broken and the cooling system was no longer working.
And why was the option of using an axial fan, as in the later VW engines, not considered? Because you would likely have needed two of them for each side, and then you would have had to cool three cylinders
in succession, as is always the case with air cooling, to the disadvantage of the second cylinder and even more so the third.
This way, the air flowed in from above, and every cylinder, especially the cylinder head, was reached by air that was just as cold. In racing engines, horizontal blowers were later introduced to provide even more
effective heat dissipation. Here, however, they were content with 1.3 times the crankshaft speed, which, at 6,000 rpm, resulted in the staggering volume of over 80,000 liters of air.
We will discuss fuel mixture preparation and other topics in the subsequent chapters on the 911. It is worth noting here the understated claim that the first series, launched in 1963, offered the same power
output, and thus the same horsepower per liter, as the latest Carrera engine.
| A cross-section of the engine . . . |
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