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Navigating the streets of Valencia, Spain is challenging enough, but the thought of doing so in an underpowered but sizeable vehicle makes this especially daunting. Along the way, there are the countless transitions in and out of roundabout intersections and the merging onto highways from very short entrance ramps, maneuvers that clearly require a vehicle with some punch. Yet there we were, climbing behind the wheel of a seven passenger VW T5 Multivan powered by a diminutive 1.4-liter four cylinder engine and thinking, "this should be interesting."
The drive was actually quite enlightening. This VW Van was powered by Volkswagen's 1.4-liter TSI engine, a powerplant intended to demonstrate the potential of engine downsizing even on larger platforms. It did its job well.
VW's TSI utilizes both a supercharger and a turbocharger to improve performance. Its belt-driven mechanical supercharger boosts performance at low rpm and aids torque and off-the-line acceleration. At higher rpm, the supercharger is disengaged to reduce parasitic drag on the engine while the "free" power of an exhaust-driven turbocharger compresses the air/fuel charge for greater high-end power. The combination, along with some sophisticated engine controls, allows the small displacement engine to deliver power equal to an engine with an additional 1.0-liter of displacement. In this case, the first generation 1.4-liter TSI motivated our ride with an impressive 168 horsepower and 177 lbs-ft of torque.
The big payback comes in the form of improved economy since the smaller displacement engine doesn't require nearly as much fuel. Burning less fuel naturally delivers a corresponding reduction in greenhouse gas emissions.
Not since the oil crisis of the 1970s has fuel economy been the priority it is today. Until recently, the North American automotive market was isolated from high and sometimes volatile fuel prices. That's changed. One of the primary options for improving fuel economy and lowering greenhouse gas emissions is the use of smaller displacement engines. Engine downsizing is a popular trend in Europe where fuel is considerably more expensive. It's a strategy that works with both gasoline and diesel engines and it's also an important factor in a hybrid's ability to deliver high mileage.
Engine downsizing to displacements significantly lower than those typically used with today's vehicles is not particularly practical without power enhancing systems like turbocharging or supercharging. Advanced cylinder head designs with four valves per cylinder and variable valve timing are also crucial to making engine downsizing viable. The goal is to operate smaller displacement engines at higher specific engine loads while delivering the same level of performance as a larger displacement engine. While this is not easy, VW's example shows it is possible. In fact, a well-engineered downsized powertrain can deliver efficiency improvements as high as 20 percent.
If downsizing is employed to enable a vehicle to operate on a four cylinder engine where a V-6 was originally needed, or a V-6 where a V-8 was required, accompanying weight reductions can mean additional savings and fuel economy improvement. Auto manufacturers spend millions each year in efforts to reduce weight in their vehicle models because, as long as strength and durability are equal while achieving weight reductions, there is no downside. A lighter vehicle will deliver better fuel economy with improved performance. All things being equal, a lighter vehicle will also accelerate quicker, stop faster, and handle better. In terms of fuel economy, the Environmental Protection Agency projects that each 100 pounds removed from an average car will realize a 1 to 2 percent improvement in fuel economy. When paying $3.00-plus for a gallon of gas, this small savings equates to 3 to 6 cents per gallon.
Downsizing isn't a cure-all. There are applications, particularly with trucks that regularly operate at higher Gross Vehicle Weight Ratings (GVWRs), where downsizing the engine might actually reduce fuel economy. If a smaller displacement engine needs to operate at higher throttle levels to move a load, it may be that a larger displacement, high torque engine would do the job more economically because it wouldn't have to work nearly as hard. The well worn automotive phrase, "there's no replacement for displacement," does have a place in this operating environment.
Most vehicles aren't operated at high loads for long. Hard acceleration from a stop is the most demanding as a vehicle's mass is set in motion, with much less power needed to maintain momentum once a vehicle is rolling. With sufficient power to deliver a satisfying and safe driving experience, a boosted smaller displacement engine will offer big fuel consumption improvements at low or partial loads.
Driving the 1.4-liter TSI Multivan around Valencia made us believers. Overall drivability was excellent and the engine had plenty of power to make the boxy T5 quite fun to drive. Volkswagen sells the twin charged TSI in a variety of vehicles worldwide, including the Golf, Golf Plus, Golf Estate, Jetta, and Touran, delivering nearly 120,000 engines to date. With more performance on less fuel ... what's not to like?
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