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

With the introduction of the '07 GMT900 trucks, you can get a 2500HD or 3500HD with an all-new body and interior wrapped around a cleaner and more powerful version of the famous Duramax diesel or a 6.0L small-block gas V-8. What you don't get is the option to buy a big-block gasoline engine or put a manual transmission behind the new Duramax diesel powerplant.

The 6.0L gas engine available in the new 31/44- and 1-ton trucks is rated at 353 hp and 373 lb-ft of torque and uses variable-valve timing along with the new 6L90 six-speed automatic to improve fuel economy. The Duramax LMM is saddled with a bigger EGR system, an intake throttle, catalysts, and a diesel particulate filter but is rated at 365 hp and 660 lb-ft of torque, which is even more than the outgoing LBZ that produced 50 percent more NOX and released 90 percent more soot into the air.

Which one of these modern V-8 engines is the best choice for you? To reveal the differences between the gas and diesel powertrains, we put both trucks on the dyno, ran them down the dragstrip, hooked up a 9,500-pound trailer, weighed them, and logged their fuel mileage while hitting the streets in all driving conditions. We'll report, you decide.

Other than the big difference in price that the Duramax diesel and Allison transmission add, the main distinction between the two powertrain choices can be found in the weight ratings. The 762 pounds of extra payload that can be carried by the Vortec gas truck is the exact difference in the factory curb weights between the two trucks. When it comes to lugging a trailer, the Duramax LMM overcomes its girth and is rated to tow 13,000 pounds using the factory hitch, which is 600 pounds more than the gasser can be counted on to pull.

Other numbers to take note of are the engine displacements. While our Ford test ("Diesel vs. Gas," Jul. '07) compared an unsophisticated 6.8L, V-10 gasser with the brand-new, dual-turbo, 6.4L Power Stroke, in this test, a 6.6L turbodiesel first designed in the late '90s has to battle it out with a high-tech 6.0L small-block with 40 years of GM advancements and a new variable-valve timing system. This should be interesting.

General SpecificationsChevy Silverado 2500HD 4WD,extended cab, shortbed, 4WDBrakesType: Four-wheel disc with ABSFront (in.): 12.8 x 1.5Rear (in.): 12.8 x 1.2

Wheels/TiresWheels: 16-inch steel (standard); 16-inch aluminum, 17-inch aluminum (optional)Tires: LT245/75R16 (standard),LT265/70R17 (optional)

SuspensionFront: Long- and short-arm independent front with torsion barsRear: Solid axle with leaf springs

SteeringSteering ratio: Variable from 13:1 to 15:1Turning circle (extended cab, shortbed): 47.6 feet

Dimensions (extended cab, shortbed)Wheelbase (in.): 143.5Overall length (in.): 230.3Height (in.): 76.8Front track (in.): 68.6Rear track (in.): 66.0Ground clearance (in.): 9.5

Manufacturing LocationsPontiac, MichiganFlint, Michigan

Shoulder room (in.)Front: 65.2Rear: 65.3Hip room (in.)Front: 62.5Rear: 61.8