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By: Conner Golden, April 30, 2015

I'm behind the wheel of a 350-hp Alfa Romeo Giulietta Quadrifoglio Verde built by global engineering consultancy AVL, and from the looks of my surroundings, I’m moving pretty fast. As the supercharger and turbocharger sing their songs in tandem while I bounce up and down the tachometer, the 1.75-liter feels downright addictive, with waves of torque and power in every gear, at every engine speed. If this is the future of CAFE-compliant internal combustion performance, everything is going to be alright for us gearheads.

The combustion experts at Austria-based AVL have been at the forefront of engine and drivetrain development and test equipment for the better part of the 20th century, working behind the scenes with major automotive manufacturers to develop mass-produced powertrain technology. Now, with a newly developed twin-charged system, they seem to have nearly solved some of the only downsides that accompany forced induction, closing the gap between naturally-aspirated engine response and forced induction packaging and efficiency. The biggest gap is low-end response, as even the best turbochargers still need some time to spool up before providing maximum boost.

AVL’s new twin-charged forced induction system utilizes a special electric supercharger to provide instant boost and power from lower engine speeds with little or no parasitic drag on the engine, quickly handing off to the large turbocharger that provides power through the upper rev range. The twin-charged setup results in an overall boost in efficiency, and engine systems can be tuned for either high-performance or to fill the torque gaps found in eco-friendly powertrains. The electric supercharger spins up via a dedicated electric motor, eliminating the need for the energy-sapping belt and pulley on traditional supercharger setups. The setup we’re driving retains the 12-volt electrical system architecture, replacing the stock battery with a deeper-cycling absorbed glass-mat battery, but future OE applications might more ideally utilize a 48-volt system.

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The Alfa Romeo Giuletta’s 1.75-liter four-cylinder equipped with AVL’s new system pushes out an astonishing 350 hp, resulting in an impressive specific output of 200 hp per liter. On the road, this translates into potent, linear power delivery at all speeds. The electric supercharger provides instantaneous low-end grunt off the starting line, helping to quickly boost exhaust flow to the turbine, and as soon as the turbocharger is producing sufficient boost, the supercharger disengages. Second gear acceleration is boundless, with power straight up to the top of the rev range. Interestingly, rather than programming for a flat torque plateau, the torque curve is contoured as to provide a linear power curve, as this has been proven to be the more ideal driving characteristic for sporting drivers.

AVL has already tested its electric supercharger on other vehicle platforms, including a Volvo, and hopes to continue developing the technology. If the near-instant throttle responses of this Alfa Romeo prototype carry over to other cars, the future of electric supercharging looks to be a promising option for automakers to balance fuel efficiency and performance.

AVL Demonstrates Electric Supercharging on 350-hp Alfa Romeo Giulietta
 

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Twin charging is the only way to get a broad power band out of a small displacement engine while achieving acceptable performance numbers. I'm not sure how I feel about the sudden push in electric superchargers, as all these things do add weight. The engine also needs to be built very stout to handle all the power while being so small, this adds cost.

There is no magical equation for efficiency and pretty soon all the BS will start being pushed by automakers. Weight, drag, gearing, and the efficiency of the engine decide the fuel consumption of the vehicle. These smaller engines do well due to the testing not pushing them hard enough to get into boost. The electric supercharger also can be tuned when to come on and off so this will be a further way to trick the system with misleading numbers. The best way to increase efficiency is by increasing the compression ratio. This is why direct injection was such a huge leap with cooling the combustion charge with out having to run a rich mixture. Diesels are more efficient for the same reason. A C6 Z06 doesn't achieve 30mpgs with pixie dust, they have a double over drive and basically idle down the highway (even at 80) but have the TQ to push the 3150 lb vehicle even though it has 505hp and 427CI engine.
 
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