Crankcase
Crankcase
Four complex components and four large sealing joints have been dispensed with thanks to the one-piece design of the crankcase and cylinder housing (including cylinder liners) as well as the cylinder head and camshaft housing. The reduced number of screw connections also contributes to the reduction in engine weight. Component integration has made it possible to save a total of approx. 45 main screw connections (50 %) compared with the previous model and therefore approx. 2.9 lbs (1.3 kg) of hardware alone.
The basic engine for the 911 Turbo was enhanced on the basis of the current 911 Carrera generation of engines with the same objective of reducing weight by integrating components and functions. Component strength was ensured taking into account the much higher loads and additional demands placed on the oil supply.
Compared with the current 911 Carrera models, the new 911 Turbo features the following main modifications:
- Crankcase with integrated cylinder housing and cylinder cations:
- Lightweight crankcase made from Alusil with special heat treatment and gas-nitrided crankshaft
- Cylinder head with modified air flow channels and improved coolant flow
- Pistons and connecting rods with modified geometry for higher loads
- Improved cooling through enlarged water pump
The fully aluminum crankcase of the new 911 Turbo is made from an aluminum-silicon alloy (Alusil) and is manufactured in a unique casting process (chilled casting). Compared with the previous model with its own cylinder housing and separate aluminum cylinder sleeves, the new crankcase is much more compact and lighter.
The basic form of the crankcase is the same as the current 911 Carrera generation. To ensure that the higher load requirements for the new 911 Turbo are met, the strength of the crankcase was increased by reinforcing the cylinder walls and using special heat treatment. In addition to the heat treatment with approx. 482 °F. (250 °C) used in the 911 Carrera engines, the 911 Turbo engine receives advance heat treatment at approx. 932 °F. (500 °C). Structural changes occur during this phase which increase strength. After a cooling phase, internal stresses are reduced in a second heating phase. This stabilises the material properties, including the desired balance between strength and expansion.
The chill-casting process enables realisation of a closed-deck crankcase with integrated crankshaft bearings. In this design, the individual cylinders are connected by a closed cylinder deck. The advantage of this design is high cylinder stability over a wide load and temperature range, which enables low friction for favourable fuel consumption.
The consistent roundness retention of the cylinders also improves the sealing of the pistons and piston rings between the crankcase and combustion chamber. Oil ingress from the crankcase into the combustion chambers and transport of the fuel-air mixture from the combustion chambers into the crankcase are thereby reduced. This improves oil consumption and also reduces performance-inhibiting pump losses in the crankcase (blow-by).
The durability of the cylinder liners was ensured in the previous model by a Nikasil(R) liner concept with a galvanically applied nickel layer. This system requires a complex coating process and can be used only to a limited extent in complex component designs. Instead of individual cylinder sleeves, the new 911 Turbo has a complex crankcase with integrated cylinders in a closed-deck construction. The crankcase is made using a special casting process (chilled casting) from an aluminum-silicon alloy (Alusil). This enables realization of durable cylinder liners using an Alusil liner concept.