Combining these two sets of data resulted in a plot of combined fuel economy against BMEP (below, right). The sweetest spot, combining the greatest power and the best fuel economy, is the upper right corner.

What does this all mean? From the point of view of fuel economy, GM leads the cars in this sample class. However, the engine being underpowered per unit volume displacement compared to the competition has some implications for the future.

Innovation in engine design and performance can lead in several directions. One is to wrest more work out of an engine of comparable size; another is to deliver equivalent work from a smaller engine. The auto industry is calling this second approach down-sizing, or right-sizing, and it is an important approach to delivering better fuel economy while maintaining customer-acceptable performance.

To look at this another way: to deliver equivalent performance to the competition, assuming it stays with its own powertrains, GM will need to use a larger engine. In fact, that’s just what is teed up for next year: a 3.9L engine that will deliver 240hp.

Then the question becomes how that might affect fuel economy. Traditionally, larger engines use more fuel. But GM has slated this engine model (named the 3900 or LZ8) to be the first V6 with Displacement on Demand (DoD)—the feature that deactivates three of the six cylinders under certain driving conditions to reduce fuel consumption. Chrysler uses its version of displacement on demand, or cylinder deactivation, in the Chrysler 300. The initial implementation of the 3900 in the Pontiac G6 will not include DoD, however.

From the GM announcement of the 3900 in October, 2003:

The 3900 is GM Powertrain’s first V-6 engine to use the unique Displacement on Demand (DOD) technology. The Displacement on Demand system was designed to markedly improve the fuel efficiency of six- and eight-cylinder engines without sacrificing performance. The system boosts aggregate fuel economy by between 6 percent and 8 percent.

[Dick] Michalski [chief engineer for 60-degree OHV V-6 engines] said the 3900’s increased displacement fits like glove-in-hand with Displacement on Demand: “A bigger engine is better when you want to maximize the amount of time the engine spends in three-cylinder operation,” he explained.

Typically, increasing an engine’s displacement also increases its fuel consumption—but not so when an engine sports Displacement on Demand. Enlarging the 3900’s displacement by 400 cc actually improves its overall fuel economy because the larger displacement translates to a greater amount of time the engine can operate in its ultra-efficient three-cylinder mode. As it turns out, bigger really is better when using Displacement on Demand.

GM’s argument, thus, is that a bigger engine is better, because it is more powerful when running in 3-cylinder mode, and then it gives a kick when needed in full cylinder operation.

But what if the same capabilities are available in smaller engines with higher performance—or a hybrid?

Earlier this year, Honda announced that it will be implementing cylinder deactivation in the upcoming Accord hybrid.

...Honda President and CEO Takeo Fukui said the Accord gas/electric hybrid equipped with a V-6 engine would deliver a higher level of performance than the 240-horsepower Accord V-6 midsize sedan while delivering fuel economy equivalent to that of a four-cylinder Honda Civic (about 28/37 mpg city/highway) compact sedan.

The car will be the first V-6 application of Honda’s Integrated Motor Assist hybrid technology and the first hybrid vehicle in the world to employ cylinder-deactivation technology. Honda’s system, which it calls Variable Cylinder Management, allows for the deactivation of half of the engine’s cylinders under light torque loads such as highway cruising. All six cylinders would be in use during most acceleration conditions. Cars.com

If Honda hits that performance and fuel economy mark, that will represent a better than 30% increase in fuel economy, with equivalent or better performance.

GM is in a tough spot. The G6 currently has the best fuel economy of the competitive sedans in that class, but it does so by being underpowered compared to all of them. To increase power, GM needs larger engines, the fuel consumption of which it will offset with technologies such as DoD. But at the same time, its competition with smaller, more powerful engines will be delivering hybrid or improved performance models themselves that offer much greater fuel economy side. (Nissan, Honda and Toyota all have announced hybrid versions of their models above.)

So the G6 wins now on fuel economy but loses on performance. In the future it might tie in performance, but it will lose in fuel economy. It seems almost contrary to the prevailing current and projected future customer demand. Right now, more customers value performance; in the future, more customers will (have to) value fuel economy.

Being at odds with the market like that is not a formula for reclaiming market share. GM should be able to do better.