While browsing the 2007 Los Angeles Auto Show we discovered Audi's 5.2L V10 FSI engine in all its 450 hp glory. It was perched on a stand in the Audi booth mated to a six-speed Tiptronic automatic transmission, and was strategically displayed amongst the S6 and S8 sedans, which it powers. We remembered reading about this engine in the January 2007 issue of SAE's Automotive Engineering International, so we dug it out to give you a rundown of its specifications. The first thing that must be pointed out is that contrary to popular belief, this engine is entirely different from the V10 used by the Lamborghini Gallardo. The Lambo engine was designed for high RPMs, while the S6/S8 V10 was put together for high torque and fuel economy.
The 5.2L V10 is built for two different outputs between the S6 and the S8 applications. The S6 receives a version that puts down 435 hp at 7000 rpm and churns out 398 ft-lbs of torque, while the S8's creates 450 hp at 6800 rpm and also produces 398 ft-lbs of torque. The varying power numbers are achieved through both its exhaust design and tuning, and the differences in output equate to relatively similar power-to-weight ratios for both cars. Follow the jump for a detailed look at the display engine along with Audi's own renderings.
The key feature that makes Audi's 5.2L V10 engine different than others is the integration of FSI technology. FSI is Audi's name for its direct injection fuel delivery system, and Audi is the first manufacturer to utilize this system in a ten-cylinder engine. In the close-up image of the engine cutaway, the injector can be seen extending into the combustion chamber on its left side. By injecting the fuel directly into the combustion chamber (as opposed to the intake runner) at an extremely high pressure, the fuel exits the injector nozzle as a vapor. This allows for increased fuel-air mixing in the chamber and thus, a more complete burn. The engine can operate at a leaner air-fuel mixture, around stoichiometric, safely without the occurrence of detonation. Fuel economy is increased and the compression ratio can safely be bumped up to 12.5:1 allowing for maximum power output.
On the backside of the engine, the timing chain drive is viewable through clear coverings. Chains are becoming common for coordination of timing as they are more wear-resistant than belts. They also don't stretch or slip which is a critical feature in order to maintain an engine tuned to meet tight emissions and performance standards. Four white cam gears are also noticeable on the engine's rear. They are hydraulically operated to continuously adjust the camshaft phase altering valve timing throughout the engine's rpm range and load conditions. This allows for the optimization of airflow into and out of the combustion chamber.
The engine also incorporates a variable runner intake manifold. Electronically controlled flaps disrupt the airflow at low engine speeds, thus ensuring the flow is turbulent. This increases volumetric efficiency as it sends more air to the combustion chamber. The intake manifold also has multiple stages. An electronically controlled valve switches the intake paths from a longer (26.6 in) to a shorter path (12.1 in). This switchover is dependent on engine speed and load, but is typically somewhere around 4,000 rpm. The longer intake path is intended to emphasis the engine's torque, while the shorter path is used reach maximum power output.
The materials used are as important as the engine design itself, so the 5.2L V10 is not without Audi's impeccable attention to detail in the materials selected for its casings, internal and external components. The crankcase is a die-casted hypereutectic aluminum alloy. Hypereutectic aluminum alloys have lower rates of undesirable thermal expansion. Also to assist in reducing expansion, grey iron bearing bridges are cast into the crankcase. They double as an aid in maintaining critical crankshaft bearing clearances by diminishing deflection under stress. Mated to the crankshaft are forged steel connecting rods and oil cooled aluminum pistons. Other notable material choices are found in the sodium-filled exhaust valves and magnesium intake manifold. The sodium melts in the heat of the combustion chamber and as the valve travels it circulates inside, acting as a heat exchanger between the valve head and the cylinder head. This increases the lifespan of the valves. The use of magnesium in the intake manifold significantly cuts the weight of an otherwise significantly heavy casting. Low weight is important to give the V10 a significant advantage over the W12 configuration.
Audi's 5.2L V10 FSI engine puts together a race-proven package in a roadgoing sedan. It uses many of the most modern and efficient internal combustion engine technologies, and shows the direction where future engine development will be directed -- as long as dino-juice is still around. There are many other design details not even mentioned. Be sure to check out the gallery to get a closer look at the engine internals or click on each image for a better view.