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I Should Have Had a Hemi!

by George on January 23, 2011

The conventional wisdom for the purchase of my wife’s car, a 2006 Chrysler 300 AWD Touring model, was that the “more economical” 3.5 liter V-6 would be more fuel efficient than the larger, more powerful Hemi V-8 engines available in the Hemi C or SRT8 versions. The prevailing wisdom, of course, it what is printed on the new car sticker, courtesy of the EPA.

Unfortunately, that “conventional wisdom” was wrong. Very wrong. The V-6 Chrysler 300 AWD proved to be a fuel-guzzler. In fact, its overall fuel mileage is quite similar to my 2008 Charger SRT8 – generally, about 18 mpg each tankful.

While it seems absurd to claim that a V-6 would consume fuel on par with a 6.1 liter Hemi V-8, you have to consider all of the variables involved in fuel consumption. The rest of the drivetrain, the driver, and environment all have a vote on fuel economy.

For example, the 3.5 liter V-6 came with a 4-speed automatic transmission; the larger Hemi also had an automatic, but it was a 5-speed. So, at highway speeds, the Hemi is barely off idle at 65 mph, but the 3.5 V-6 is, as expected, doing a bit more work with one less gear available. The real problem with the smaller motor comes into play during the slightest of inclines or a stiff headwind.

The V-6 simply lacks the necessary torque at lower engine speeds to keep the transmission in its top gear. The subsequent downshift to third gear requires the engine to run at a much higher speed to maintain momentum on inclines or in headwinds. This consumes a great deal more fuel. By contrast, the 6.1 liter Hemi will loaf along in top gear virtually unperturbed by the presence of wind or hills; the smaller 5.7 liter Hemi would do this with only 4 cylinders by virtue of of its multi-displacement system that shuts off half its cylinders under light load.

But perhaps the single biggest influencing factor in fuel economy is the driver. Since my wife’s throttle inputs are somewhat akin to the kinetic reflex of a startled mule, her fuel mileage results are, at best, disappointing. The jack-rabbit starts and 4,000 rpm upshifts have a cost. By contrast, my velveteen caress of the Charger’s go-pedal illicit forward movement without drama and upshifts typically occur 2,000 rpm sooner. She gets around 17-18 mpg in her V-6; I get 18-19 with the 6.1 liter Hemi.

Still, even when I drive her V-6 silky-smooth and do my utmost to keep it in the highest gear possible, I’m still lucky to get anything more than 23 mpg during mostly highway driving. While the smaller motor ends up eclipsing the Hemi’s 21 mpg average under these same conditions, it requires the same type of concentration you would need to land a jet on the deck of an aircraft carrier.

Had I followed the axiom that states “there is no replacement for displacement” I would have bought the Hemi C. Not only would we have enjoyed more thrust and more perks – we might have paid for those perks through improved fuel economy.

Our error was not necessarily following conventional wisdom about fuel economy. We erred in not questioning it. Caveat emptor!

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