Chevy Duramax LMM Diesel Vs. 6.0L Vortec LY6 Gas Engine- Diesel Vs. Gas

Average441.30 miles / 37.31 gallons = 11.83 mpg

Average511.70 miles / 43.47 gallons= 11.77 mpg

Noise TestThe diesel particulate filter has nearly eliminated visible smoke emissions from the tailpipe, so the main drawback to owning a diesel may be the added noise of the compression-ignition process. The Duramax line of engines has been famous for low noise since it was introduced in the '01 GMT800 trucks, and the new LMM is the quietest version yet. The diesel particulate filter, multiple catalytic converters, and a bazooka tailpipe all play a role in breaking up annoying sound waves.

The only time the diesel was quieter than the gasser was during wide-open-throttle acceleration that caused the 6.0L engine to growl at 89 dB, while just 85 dB were created by the new Duramax LMM. The interior noise of the diesel at idle was only slightly louder than that of the gas truck, but exterior noise at idle was noticeable (just ask the fast-food attendant on the other side of the intercom).

City speeds kept the Vortec engine relatively quiet around 45 mph, where it beat the diesel by a large, 15dB margin. Plus, the diesel had noticeable turbo whine in medium speed conditions (we love it, but you may not). Out on the freeway, the field was fairly even, with the Duramax registering only 1 dB higher on our unscientific equipment. The numbers are so close, you could call it a tie, but we'll trade that single decibel for the extra 244 lb-ft of torque made by the Duramax any day of the week.

Duramax LMM 6.6L TurbodieselInterior at idle: 69 dB45-mph cruise: 84 dB75-mph cruise: 88 dBWide-open throttle: 85 dB

Vortec LY6 6.0L GasolineInterior at idle: 66 dB45-mph cruise: 69 dB75-mph cruise: 87 dBWide-open throttle: 89 dB

Towing Test: Steep Grade at 15-65 mphTo see how the small-block gasser truly stacks up against the Duramax, we hooked up a 9,500-pound trailer Suburban 4x4 combo and attacked a steep grade at an altitude of more than 3,150 feet. We started by rolling along a freeway onramp at 15 mph and timed how long it took to reach the speed limit of 65 mph. Two attempts were made with each truck, and Editor David Kennedy was able to knock almost 3 seconds off the gas truck's first pass by manually shifting the 6L90. We decided not to try and outsmart the Allison transmission because the shifts during the first pass seemed to be right on when the Duramax pulled the grade.

Duramax LMM 6.6L TurbodieselTest 1: 24.8 secondsTest 2: 24.1 seconds

Vortec LY6 6.0L GasolinePass 1: 33.3 secondsPass 2: 30.6 seconds