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An article by veteran automotive journalist Gary Witzenburg for AutoblogGreen discusses the results of a 3-year study by the National Research Council (NRC) on the cost-effectiveness (or lack thereof) of various fuel-saving measures and technologies available to auto makers. Here are the most relevant excerpts from Witzenburg's article:

The study concludes that a traditional gasoline engine with a portfolio of advanced technologies can reduce its fuel consumption by about 29 percent at an added (consumer) cost of $2,200. To compare, an advanced "clean" diesel engine offers a 38 percent reduction at an average added cost of $5,900 and a full hybrid a hefty 44 percent improvement for $6,000.

Accompanying CAR's summary is a chart ranking 28 of those technologies available now or soon by their incremental cost to the vehicle buyer per one percent fuel-economy improvement.

Technologies / Average Incremental Cost / Average Cost for 1% Improvement in Fuel Consumption
Low Viscosity Lubricants $6 $12.00
VVT-Coupled Cam Phasing (CCP), OHV $53 $21.00
Variable Stroke HVAC $80 $22.86
Turbocharging and Downsizing $129 $25.80
Low Rolling Resistance Tires $40 $26.67
Aerodynamics 5%-10% $45 $30.00
Electric/Hydraulic Power Steering $95 $31.67
Valve Event Manipulation $52 $34.67
7 Speed Transmission $235 $39.17
VVT-Coupled Cam Phasing (CCP), SOHC $105 $42.00
VVT-Dual Cam Phasing (DCP) $105 $46.67
Dual Clutch Transmission $350 $46.67
Continuous Variable Transmission $207 $51.63
8 Speed Transmission $425 $60.71
Valve Event Manipulation (Variable Value Lift) $760 $69.09
VVT-Intake Cam Phasing (ICP) $105 $70.00
Cylinder Deactivation, OHV $353 $70.50
Engine Friction Reduction $95 $75.60
Continuously Variable Valve Lift (CVVL) $450 $90.00
Mass Reduction 5% $297 $91.38
Mass Reduction 10% $713 $109.69
Cylinder Deactivation, SOHC $555 $111.00
Full Hybrid $6,000 $127.66
Discrete Variable Valve Lift (DVVL), SOHC/DOHC $293 $130.00
Mass Reduction 20% $1,600 $133.33
Stoichiometric Gasoline Direct Injection (GDI) $319 $141.78
Conversion from Gasoline to Diesel $5,900 $159.46
Stop/Start Hybrid $885 $221.25

At the very top is low-viscosity lubricants at an average incremental cost of just $12 per one percent fuel consumption improvement. Next comes coupled cam phasing (variable valve timing, or VVT), which varies both intake and exhaust valve timing simultaneously, on an OHV (pushrod) engine at $21 per one percent gain.

Downsizing engines and adding turbocharging to recover lost performance – which, coupled with direct fuel injection, Ford markets as EcoBoost – falls a surprising fourth on the chart at about $26 per one percent. Just below that are low-rolling-resistance tires at about $27, a 10-percent aerodynamic drag reduction at $30 and electro/hydraulic power steering (vs. conventional hydraulic) at nearly $32.

Second from the bottom is that $5,900 diesel at nearly $160 per one percent improvement. At the very bottom is a stop/start hybrid, fairly affordable at $885 total but costing a hefty $221 per one percent. By contrast, the $6,000 full hybrid system is nearly twice as cost effective at about $128 per one percent efficiency gain.

Looking at various valvetrain enhancements, dual cam phasing is good for about $47, variable valve lift (VVL) comes in at $69 and cylinder deactivation of a pushrod engine – General Motors ' Active Fuel Management (AFM), Chrysler's Multi-Displacement System (MDS) – at just over $70 per one percent. A seven-speed automatic transmission (presumably vs. the once-common four-speed) adds roughly $39, a dual-clutch gearbox $47, a CVT (continuously variable transmission) $52 and an eight-speed automatic $61 per one percent improvement. Further down the chart are vehicle mass reductions of five percent ($91 per one percent), 10 percent ($110) and 20 percent ($133) and gasoline direct injection at about $142.

What all this means is that, as CAFE requirements accelerate upward over the next several years, each automaker will have to pick and chose from a menu of such fuel-saving technologies and decide which combinations are most cost-effective. Then we, as potential buyers, will compare and decide which models from which makers will best suit our needs while delivering the best fuel efficiency at the most affordable prices.

At Witz' End - Comparing costs and benefits of fuel-saving technologies — Autoblog Green
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