wieder ein Thread zu Motorschäden "Tschüss Porsche - der Motor ist im Eimer ..." motiviert mich zu diesem Beitrag.
Im Netzt lese ich viel über die Motoren der unterschiedlichen Baureihen. Über Foren hinweg gibt es Verächter der neuen Konstruktionen (ein gewisser "flieger" war hier ja auch mal aktiv) und Lobhudeleien der Mezger Konstruktionen.
Nakasil, Lokasil und Alusil und was ist denn jetzt wo zu finden; außer bei den GT-2, 3 und Turbo herrscht da Verwirrung.
Und der neue Turbo ist nun auch kein Mezger mehr ...
In einem britischen Forum habe ich die bisher beste Zusammenfassung gefunden, was die Änderungen (Verbesserungen) bzgl. der aktuellen DFI Motoren betrifft. Nach der Lektüre kann ich mich mit dem 997.2 entspannt zurücklehnen.
Hier ist der Forenbeitrag:
(eine Frage noch zusätzlich an die Experten wie 996-Frank und racertb und Andere: was ist von dem Einsatz der Stahlbuchsen zu halten, den z.B. die Fa. Theimann anbietet? Ich frage aus rein technischem Interesse)
Von Ian_UK1 am 6. Mai 2011 in Piston Heads ( http://www.pistonheads.com/gassing/topic.asp?t=999473
If these engines coke-up like other DFI engines, yes it bl**dy does matter! I don't want a car that only makes 300BHP in a couple of years time because of the valves being choked with crap and Porsche doing a 'What problem sir...'? I'll put good money on Porsche NEVER decoking one of these engines under warranty.
For the moment, this whole topic is on hold until I get (or someone else gets) a borescope down the inlet tract of one of the DFI engines and we can assess the extent of the coking problem. There will be one as all DFI engines (and Diesels) have this issue to a greater or lesser extent - it's just a case of how much and what effect it has on the engine's output.
As for the machanical issues - yes the DFI engine seems to have cured all the previous generation's ills. Anecdotally, there's no tales of woe on forums across the world and technically, they addressed all the right parts of the engine. Below are some excerpts from the Porsche Technical manual about relevant changes to the new engines:
A totally redesigned generation of engines is used for the new 911 models. As on
the previous model, these engines have a different displacement -
a 3.6-litre flat-six engine is used on the 911 Carrera, while the 911 Carrera S has a
3.8 litre flat-six engine.
Although the displacement is the same as on the previous models, the performance
and torque have been increased significantly, while fuel consumption is reduced by
This was primarily achieved through the use of direct fuel injection (DFI), by reworking
the intake and exhaust system and by improving the engine internally in order
to reduce friction and drive losses. By reducing the oil pan height, it was possible to
lower the installation position of the engines by approx. 10 mm, thereby lowering
the vehicle’s centre of gravity and improving driving dynamics.
The new 911 models feature a two-part, vertically split crankcase with an integrated
crankshaft thrust block. The advantage of this design is that smaller components
can be used, while the separate bearing saddle with cast-in cast iron elements is no
longer needed, thereby reducing the overall weight of the engine.
The actual crankcase on the new 911 engines is made completely of an aluminiumsilicon
This procedure offers the following advantages:
• With ALUSIL, the crankcase can be made from one cast, without cylinder
sleeves and without having to coat the cylinder bores afterwards.
• ALUSIL is an excellent heat conductor and thus allows high specific engine
• ALUSIL has excellent friction properties. Since the pistons and piston rings
slide on the exposed silicon crystals, they have a low tendency to seize.
• ALUSIL does not present any recycling problems because the crankcase
does not include any foreign materials, e.g. cast-in cast iron cylinder sleeves.
The listed advantages of the alloy are certainly important arguments in its favour.
Indeed, the low-pressure chill-casting procedure, which has since proved to be the
best solution by far for casting ALUSIL, is an important prerequisite for reliable,
mass-produced crankcase cast parts.
Cylinders are now connected differently in the cylinder-head cover area. The individual
cylinders, which originally stood freely in the water jacket (open deck design),
are now connected by a closed cylinder deck (closed deck design). The advantage
of this design is high cylinder stability, particularly the cylinder shape (roundness
and low cylinder deformation) over a wide load and temperature range. This has the
added advantage of reducing friction and thus reducing fuel consumption. Even
piston and piston-ring sealing has been improved as a result of the higher retention
of roundness of the cylinders. The entry of oil from the crankcase into the combustion
chambers and the entry of the fuel-air mixture from the combustion chambers into
the crankcase is reduced. This both improves consumption and reduces performance-
inhibiting overpressure caused by blow-by in the crankcase.
The drop-forged crankshaft runs in eight bearings and has twelve counterweights.
Main bearing 4 is designed as a thrust bearing. Axial play is determined by two
thrust plates, which are inserted at the left and right of the bearing.
The main bearings are designed as plain bearings with a diameter of 63 mm. Main
bearings 1/3/5/7/8 are smooth bearings, while main bearings 2/4/6 are grooved
bearings. These grooved bearings supply oil to the lubrication points of the crankshaft
The drive mechanism for the two drive chains for the camshafts and demandcontrolled
oil pump is located on the pulley side.
The piston crown temperature in the 911 Carrera engines is reduced by means
of piston injection cooling. The spray nozzles are forced-fitted into the crankcase
and cannot be replaced. To ensure the necessary engine oil pressure at low revs
and high engine oil temperatures, these spray nozzles only open at a higher oil
Another special feature of the new generation of engines is that these engines no
longer have an intermediate shaft. This drive shaft, which was fitted between the
crankshaft and the camshafts on previous models, was required in order to reduce
the transmission ratio and thus the dynamic forces of the timing chains. Through
the use of new, high-performance timing chains, it was possible to simplify the drive
mechanism for the camshafts in spite of higher revs, thereby reducing the weight of
the engine significantly by removing the intermediate shaft. Together with an additional
crankshaft bearing location, this allows greater stability and a significantly higher
engine speed potential.
The oil supply in the new generation of engines has been essentially redesigned
with the following objectives in mind:
• To ensure the supply of oil even during very high lateral and axial acceleration
• To reduce friction and drive losses
The main differences between the new oil supply system and that used on previous
models are as follows:
• Additional oil extraction point in the cylinder head
• Electronic demand-controlled oil pump
• Additional watertight sheetmetal panel between crankcase and oil pan
Compared with the previous models, the new 3.6 and 3.8-litre engines have not
only one, but two extraction points in each cylinder head. In addition, the new 911
engines now have a total of 5 oil pumps instead of 3. These are located in the oil
pan and are driven by a shared shaft. They include 4 extraction pumps for the
cylinder heads (2 per cylinder head) and a new demand-controlled oil pressure
As you can see from the above, almost all the points that have been described by Hartech and others (and identified as potential weak points in the M96/7 engines) appear to have been totally redesigned. The exception, as it's not described in the technical manual (other than via a couple of diagrams) is the cooling system, so I have no way of knowing how the system is designed on the DFI motors or whether the idiosyncrasies of the previous generation engine are repeated.