After recently driving the B8.5 S4 with its lovely V6 Supercharged engine and with the all new B9 generation of the Audi S4/S5 starting to appear more frequently on the road, I thought it would be a good time to look at the new heart of the beast.
The all new turbocharged V6.
- Reverse flow header (which makes using twin-scroll turbocharger possible)
- Integrated exhaust manifold into the header
- Cast-in iron cylinder liner (not Alusil, which is an aluminium-silicon alloy, like in the old supercharged V6)
- Direct injection system changed to spray-guided type (Audi has been using air-guided type previously)
- Single turbocharger with twin-scroll design
- Introduced Miller cycle (a.k.a Atkinson cycle) in its operation
- Air-to-air intercooler
- Modified version to be shared with the 2017 Porsche Panamera in V6 form
- Bore pitch/spacing: 93 mm
- Displacement: 2,995 cc
- 354 hp, 369 lb-ft (500 Nm) @ 1,300-4,500 RPM
Now let’s look at the new engine in a little more detail.
The below image indicates the new turbo V6 is still using the closed-deck design, same as the previous supercharged V6:
One major change is the cylinder sleeve. On the new V6, Audi is using cast iron cylinder sleeve, totally different than the old supercharged V6, which is using the Alusil layer. If you ever drove the B7/8 and experienced excessive oil consumption, this should be eliminated in the new B9 engine.
Due to the lightweight design principle, the new V6 only weights at 172 kg, a significant decrease from the predecessor’s 189 kg.
The new V6’s 90-degree bank angle, means it will naturally require uneven firing, Audi uses offset split crank pins to correct this. The 90-degree geometry also brings in unbalanced vibrations, so that is the reason why you can see in Audi’s design, an extra balance shaft is added on top of the crankshaft, as shown in the below illustration.
Reverse Flow Header
The new B9 S4/5 will be the first modern turbo V6 that uses the reverse flow design.
Reverse Flow means the exhaust manifold is on top, and the intake is on the side. The reason that Audi has chosen such a design is in order to adopt the single twin-scroll turbocharger for the V6 engine, without complex pipping and routing.
A design like this minimises the path length that exhaust gases need to travel to reach the turbocharger, which means better throttle response and less (or no) lag.
Turbocharger: Why No Twin-Turbo Units?
The benefit of using a a single twin-scroll turbochager gives better throttle response in the lower RPM range, whilst the tighter flow volume can limit high RPM and high load driving.
Whereas the use of twin single-scroll turbochargers, is that the boost can still be kept strong for high RPM workload, which helps the engine to reach a very high peak output. But throttle response in the lower RPM range will be impacted.
In the S4/S5’s this engine makes 354 hp, not high enough to justify the twin-turbo plan, so this is the reason why Audi engineer select the single twin-scroll chargers as the final solution.
Generally speaking, for a 6-cylinder engine with around 3.0L displacements, if its application is aiming at output level around 350hp, a single twin-scroll turbocharger brings more benefits than disadvantages. BMW have also gone down the same route in their new 3.0l B58 engine.
The cylinder head’s cooling loop
Due to the centre of the V bank valley being occupied by the turbocharger, which is a preferable mounting location if it wants to use the air-to-liquid type; on the other hand, relocate an air-to-liquid intercooler to other places of the engine is not beneficial too. Therefore the packaging constraint prompts Audi to use the air-to-air type intercooler, as you can see in the below picture.
There are separate coolant paths in the engine’s crankcase and cylinder head.
Co-developed with Porsche, this new turbo V6 has the same advance level as BMW’s B58 engine.
Compared to its predecessor (the 3.0L supercharged V6), the new V6 is much lighter, which is critical for Audi vehicles since they are all based on the FWD layout, and puts the engine 100% ahead of the front axle. The new engine is more efficient too, due to the elimination of mechanical air compressor, and also the adoption of spray-guided direct injection.
This turbo V6 will be also used in next-generation of the Porsche Panamera (starting at model year 2017). However, in Porsche’s application (and perhaps the future Audi RS4/RS5) the current cast-in iron cylinder liner will be replaced by plasma spray coating layer, for better performance.
So it looks like Audi have heavily invested in this engine for the future of their performance brand, now I just need to get hold of one to test drive and compare to the old supercharged lump!