Next S4 to be supercharged
Audi is embracing supercharging technology in a bid to blend fuel-economy and power in their new 3-litre TFSI, allegedly bound for the new S4.
Performance demands, market realities
With escalating oil prices engaging car buyer to make strong purchasing decisions towards frugality, manufacturers’ have had to redouble their engineering efforts in providing market relevant power plants able to deliver good fuel economy and requisite performance.
Stringent emissions and fuel-economy regulation have rendered the venerable 4.2-llitre V8, which has done sterling service in Audi performance models, to the performance history scrapbooks. Employing a forced induction engine to replace it would provide Audi with the flexibility of tailoring boost application for a variety of models whilst keeping pace with changing enviromental regulations.
Already a notable purveyor of turbocharging, Audi, harked back into their rich pre World War Two Auto Union racing heritage to rekindle a strong relationship with supercharging. A blend between forced induction technology and direct-injection yields the new 3-litre TFSI V6 petrol engine, both powerful and comparatively light on fuel.
Common-rail direct injection petrol – huh?
Audi’s exhaustive research revealed a supercharging solution as providing a superior performance to economy coefficient compared to the biturbo concept.
Common-rail direct injection, once nearly exclusively the domain of advanced diesel engines, has aided the supercharging exercise tremendously in terms of packaging whilst simultaneously providing fuel injection pressure of 150 bar.
The 3-litre TFSI runs at a 10.5:1 compression ratio – quite high for an engine featuring forced induction following conventional wisdom. Fortunately the direct-injection system, which feeds fuel into the combustion chamber at high pressure, causes a swirling effect which also actively cools the combustion chamber, reducing potential knock.
Boosting to efficiency
Nestled between the two cylinder banks, the Roots-type supercharger happily slots in where the intake manifold would be traditionally. Driven by the engine via a poly-V belt, the Roots-type ‘blower’ provides a 0.8 bar of maximum boost with practically no lag.
Twin aluminium water-to-air intercoolers are fed by separated coolant circuits to ensure optimal operating temperature is maintained. Ensuring a seamless interface between the supercharger boost and combustion are the two intake camshafts – once on each cylinder bank – which can be adjusted through 42-degrees on the crankshaft angle.
The net result of all this technical wizardry is a 3-litre, long stroke engine producing 213kW at 5 000r/min and 420Nm at between 2 500r/min and 4 850r/min. These figures night not match the award winning BMW 3-litre twin-turbo for outright power – 225kW versus 213kW – but it does best the Bavarian in a torque output comparison – 420Nm versus 400Nm.
Rumour has it the 3-litre TFSI engine has massive latent tuning potential, fuelling speculation the S4 will have in the region of 253kW on demand. The 'stock' version is expected to do duty in the forthcoming A6 and A8 ranges.
Although the entire exercise is heavily influenced to ensure very low fuel consumption Audi is at yet mum on exact average consumption figures for the ‘stock’ 3-litre TFSI, commenting only that it will be, “well under 10l/100km.”
So, as the oil-crisis drives unprecedented changes in consumer behaviour, manufacturers are reacting to these two powerful market forced by providing requisite performance with a blend of petroleum efficiency never before though possible.