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A Guide To The Future Of High MPG: It's About Efficiency, Not Economy.

Rex Roywriter

Enthusiasts have reason to be concerned about high-performance cars being regulated out of existence. Consider the recent passage of the Obama administration's new CAFE standards as well as the looming specter of cap and trade carbon taxes. Some Draconian scenarios predict an over-regulated future filled with dull cars.

More hopeful readings of the vehicular tealeaves portray a vibrant automotive market. For the sake of this article, we'll operate under the assumption the industry is headed in this happier direction. Based on decades of trend watching, technology is the avenue automakers will take to meet new regulations while still providing exciting levels of performance.

There is no one correct path to the future and automakers will likely use a variety of strategies and combinations of technologies to reach their government-set goals. To help identify possible tracks, this article looks at five different highly efficient vehicles that could foreshadow things to come:

You will likely agree that none of these cars is dull

2010 Chevrolet Corvette
Environmentalists have succeeded in categorizing C02 as a harmful greenhouse gas. While some believe that the argument over C02's effect is completely understood, legitimate scientists counter the negatives may not exist at all. Regardless of whatever the truth may turn out to be, C02 is a byproduct of combusting carbon-based fuels, and to meet future emissions regulations, vehicles must burn less fuel. On this, math is math and everyone agrees.

Currently, the 2010 Chevrolet Corvette takes a decidedly Detroit approach to fuel efficiency. Its powertrain formula matches a large displacement, high torque engine to a drivetrain that features tall gearing. Packaged in an aerodynamic body with a chassis that features minimized rolling resistance, the big engine barely needs to rev above an idle to motor the Corvette down the road.

The stock 430-horsepower LS3 generates 424-lb-ft of torque at 4600 rpm, but more than 300 lb-ft is available at 1000 rpm. This would be the definition of low-end grunt. Transmission gearing for 5th and 6th gears is 0.71 and 0.50:1, which translates to a 70 mph cruise with the engine barely turning 1500 rpm for cars equipped with a six-speed manual gearbox and the standard 3.24:1 final drive ratio. Given room to run in 5th gear, thusly equipped, the base Corvette can achieve 190 mph.

With an aerodynamic Cd of just 0.286, the Corvette officially achieves 26 mpg on the EPA highway cycle. Unofficially, the web and some respectable media outlets are full of anecdotal evidence of Gen 6.5 Corvettes averaging over 31 mpg at highway speeds.

The Corvette's approach to efficiency yields huge benefits on the performance side of the equation. The same features that benefit fuel economy are plusses on the performance side of the ledger. When the big 6.2-liter overhead valve V-8 wakes up from its idle, its 424 lb-ft of torque generates serious hustle. Given a grippy launch surface and feet like Fred Astaire, one hits sixty mph in just 4.2 seconds. Mileage for that sprint will, however, be less than the Corvette's city rating of 16 mpg.

Greenies and bureaucrats choose to only recognize the Corvette's more aggressive side, while ignoring its efficiency. This makes America's sports car a favorite object of ire. If these groups only knew how efficient the 2010 Chevrolet Corvette was, perhaps they'd pick on somebody else and show Detroit a little love.

2010 BMW 335d
A decidedly different approach to efficiency is embodied by the 2010 BMW 335d. The technically sophisticated and more costly approach relies on a sequentially turbocharged, compression-ignition engine.

The 3.0-liter in-line six-cylinder BMW diesel produces 265 horsepower at 4200 rpm. While the horsepower is nothing to write home about, its torque bests the Corvette at 425 lb-ft, and this peak comes at just 1750 rpm. Driving the rear wheels through a conventional six-speed automatic, 0-60 mph performance (about 6 seconds flat) is similar to that of a V-8 sedan, but its fuel economy -- 23 mpg city, 36 mpg highway -- shames some four cylinder economy cars. Top speed for 335d models with the Sport Package is 149 mph.

Here's how the BMW achieves its numbers: Diesel engines are hearty by nature. Their heavy-duty construction is needed to handle static compression ratios that would turn gas-fueled mills into grenades. The BMW 3.0-liter utilizes a 16.5:1 static compression ratio and injects fuel directly into each cylinder at 26,000 psi.

This precisely metered and fully atomized fuel charge combines with a pressurized air charge that's the product of sequential turbochargers. The twin turbos are not a matched pair as they are on the 2010 Ford Taurus SHO. One is small and the other large. The light mass of the small turbo enables it to spin up quickly, and it alone produces boost from approximately 700-1500 rpm.

As engine speed increases, there is enough exhaust energy to spin up the larger of the two turbos. From 1500-3200 rpm, both blowers add boost. Above 3200 rpm and to the engine's red line, the efficiency of the small turbo falls off and the boost duties fall to the larger unit. Maximum boost from the turbos is 23.9 psi above atmospheric.

This approach comes with a cost that BMW pegs at about $2500 for comparably equipped vehicles (335i with an automatic transmission compared to a 335d). This premium is directly related to hardware costs. The high-pressure fuel-injection system and turbos account for roughly 75-percent of the upcharge, while the multi-stage exhaust system consumes the rest.

To make the diesel clean enough for North America, the 335d's exhaust requires an oxidation catalyst, a diesel particulate filter, a urea dosing module, and a selective catalytic reduction catalyst. These components aren't free, nor is the urea refills required to keep the 335d on the road (it will not start if the urea tank is empty).

While costly, the approach works, and if CARB ever gets its head on straight, diesel-powered vehicles like the BMW 335d could be a hit in America.

2010 Porsche 911
Another efficient six-cylinder solution featuring direct fuel injection is offered up by Porsche. Porsche fans have followed the roll out of direct injection throughout their brand; first on the non-turbo 911 models in 2009, then later that year to the Cayman S/Boxter S models, and most recently to the 2010 911 Turbo that will debuted at the 2009 Frankfurt show.

By itself, direct injection delivers increases in both power and efficiency. The gains vary by application, but estimates range from 5-10 percent, give or take a few. For those who need a primer on DI, our own Don Sherman wrote a piece on the technology when it was selected as
Automobile Magazine's 2009 Technology of the Year.

Suffice it to write that having a computer-controlled, high-pressure (200 psi) piezoelectric injector firing atomized fuel directly into the combustion chamber works wonders for efficient combustion. A staged, or stratified, injection of fuel burns better than one single squirt, and helps the 2009 911 with the 3.4-liter flat-six produce 20 more horsepower (345 hp) than in 2008 while achieving a 13-percent fuel economy improvement. Part of the gain comes from a higher compression ratio (12.5:1 vs 11.3:1 for 2009 vs. 2008) that the stratified fuel charge makes possible.

These gains from the engine are added to by Porsche's first mass-production version of its PDK double-clutch transmission (Porsche-Doppelkupplungsgetriebe). While Porsche has used this technology for two decades in racecars, none of the brand's volume road cars have benefited from this seven-speed gearbox.

In principle, the PDK consists of a conventional manual gearbox and a hydraulic control system divided into two separate transmission units. Two hydraulically controlled wet clutches in radial arrangement form the heart of the transmission. One clutch is for the first transmission unit with the uneven gear ratios (1, 3, 5, and 7) and reverse, and the other clutch is for the second transmission unit with the even gears (2, 4, and 6). Via a number of pressure valves, the hydraulic control unit masterminds both the wet clutches and the shift cylinders activating the transmission ratio required.

Compared to a traditional automatic transmission or Porsche's own Tiptronic S (no longer available on the 911), Porsche's PDK saps less powertrain energy, thus helping improve the fuel economy of 911 models fitted with the technology. Having five closely spaced gears helps keep the engine operating in its most efficient range when driving around town. Additionally, the PDK's top two gears are overdrive ratios, 0.88 and 0.62:1. These tall ratios help keep engine speed lower at highway speeds, another dynamic contribution to fuel economy.

Certainly, the base 911's performance hasn't been compromised in any way as the company pursued improved efficiency. The factory states that the top speed for a PDK-equipped 911 is 178 mph, and 60 mph gets passed at the 4.7-second mark.

2010 Ford Taurus SHO
Ford Motor Company talks about its "Plan For Sustainability" at nearly every major product press conference. The plan highlights how FoMoCo will deliver vehicles that people will want to drive while meeting the government's new CAFE and emissions regulations. Greenies and government types rejoice when they hear phrases like "enhanced sustainability," and "reduction in carbon consumption."


What's truly important are the facts, not the blather, and Ford's plan is reasonable because it's technology- and fact-based. Their strategy employs using smaller displacement engines to help boost its corporate fuel economy numbers. But Ford knows that Americans want performance, so these smaller engines will feature turbocharging and direct fuel injection to boost power. Eco and Boost -- get it?

AutomobileMag.com has recently driven four EcoBoosted products including the 2010 Lincoln MKS, Lincoln MKT, Ford Flex, and Taurus SHO. The first three models get a 355-horsepower version of the 3.5-liter twin-turbo V-6, while some secret sauce gets added to the SHO's engine to boost power another 10 hp. In these applications, the EcoBoost variants deliver about 100 more horsepower than the naturally aspirated, non-DI version while achieving identical EPA mileage. (Note: to manage the power, these EcoBoost models all feature all-wheel drive. Economy figures are compared to naturally-aspirated models with all-wheel-drive to make the comparison apples to apples.)

Unlike some turbo cars of yore, when the driver goes WOT (wide open throttle) in the Taurus SHO, there is no turbo lag. The matched set of Garrett turbos are so small, that almost any time the engine is running, the blowers are ready to produce instant boost. The max fed into the manifold is 12 psi.

Modern engine electronics give the SHO 350 lb-ft of torque from 1500 revs on up to near the horsepower peak (5250 rpm). The torque curve really isn't a curve, it's a broad, flat plateau that results in effortless acceleration at any speed. Turbo waste gates bleed boost pressure to maintain that plateau, and its acceleration comes on in a linear fashion. The magic 60 mph appears in under six seconds, while quarter miles are effortlessly dispatched in about 14 seconds at about 100 mph. Not bad for a two-ton-plus sedan that achieves 17/25 mpg.

With the 3.5-liter, Ford is using EcoBoost as a substitute for using a larger displacement engine in high-performance applications. Plans call for an expansion of the technology's deployment. The 3.5-liter V-6 will end up in the F-150 and may become an option in the Mustang. Another EcoBoost engine will be a 2.0-liter four-cylinder that could be used in a variety of vehicles including the company's mainstream sedans. The 2.0-liter EcoBoost matches the power of many naturally-aspirated V-6 engines while still delivering the economy of a four-cylinder.

Ecoweenie blather aside, EcoBoost works. You'll certainly be seeing more of it.

2010 Lexus RX450h
Totally restyled for 2010, the Lexus RX is the benchmark for luxury crossovers. Cadillac and Audi are both gunning for it with the all-new SRX and Q5, just as Acura, Mercedes-Benz, and BMW have been doing for years. The gasoline-powered RX350 is easily the best-selling Lexus and luxury crossover in 2008-2009, just as it has been since it was introduced in 1999.

Despite the fact that the all-new 2010 RX350 offers little excitement for enthusiasts, the hybrid technology behind the RX450h is something one can sink their teeth into.

Lexus improved the 3.5-liter V-6 engine for the new RX350 so that it produces more power (275 hp) with better mileage of 18/24 mpg city/hwy. The transmission is an all-new six-speed automatic (up from a five-speed in 2009). But the 2010 RX450h uses its hybrid drive to amp up (sorry) the RX's performance.

Beyond delivering 30 mpg city, 27 mpg highway, the RX450h is rated at 295 horsepower, 20 more than the conventionally-powered RX350. With the Atkison-cycle 3.5-liter V-6 opened up, the engine itself produces 245 horsepower. The late-closing intake valve of the Atkison cycle helps improve the engine's efficiency, but comes with a loss in power compared to a conventional Otto-cycle four-stroke engine.

This power loss is more than made up for by another 50 horsepower from the hybrid's two motors; one where you'd expect the transmission to be, and a second where you'd expect to find the rear differential. More important than the horsepower is the valuable torque these motors generate with juice from the 288-volt nickel metal hydride battery array. Because the torque from these motors is heavily managed, Lexus engineers won't release their torque ratings, but their contribution is significant and well into three digits of oomph.

Lexus engineers employed other tricks to maximize the efficiency of the RX450h. To get the engine to peak operating temperature quickly, there is a heat recovery system connected to the exhaust system (and it's more than a foil tube hovering over an exhaust manifold like in the old days). Cooled exhaust gasses are also introduced into the intake charge to make the mixture more dense and powerful. Additionally, the power steering is electrically assisted, eliminating the need for a constantly running drive belt.

The complete hybrid drive system provides performance that feels as lusty as some competitors with V-8 engines. The fact that two motors function as a continuously variable transmission mean that acceleration comes on, and stays strong. Should an RX driver ever want to brag about their vehicle's 0-60 mph time, it's about 7.6 seconds, identical to the gas-RX, even though the hybrid is heavier. While softly sprung it its standard form, the firmer Sport package adds some entertainment to what is already a highly efficient vehicle.