Dyno TestAlthough DC Performance specializes in SRT-10 Dodge Rams and Vipers, the staff was happy to take part in our Chevy slugfest. Both trucks were strapped to the same dyno to reveal the true stock horsepower and torque ratings. Chevy rates the gasoline-powered Vortec LY6 engine at 353 hp and 373 lb-ft of torque, and the Duramax LMM is said to make 365 hp and 660 lb-ft of torque at the engine's crankshaft. The gas truck had trouble staying in Fourth gear when the engine was loaded, so the rear-wheel power and torque ratings are a bit lower than expected. It should also be noted that the new 6L90 six-speed automatic in the gasoline truck doesn't have a direct drive speed (Fourth gear has a ratio of 1.15 and Fifth is 0.85), so the gearing may have affected the final numbers. As expected, the Duramax LMM put down a lot more torque on the dyno, making 244 lb-ft more at the rear wheels.
6.6L Duramax LMM Turbodiesel V-8 Max power: 303 hp at 3,200 rpmMax torque: 507 lb-ft at 2,700 rpm
6.0L Vortec LY6 Gasoline V-8Max power: 279 hp at 5,900 rpmMax torque: 263 lb-ft at 4,800 rpm
Drag RacesDuring our final trip to the now closed Los Angeles County Raceway in Palmdale, California, we raced the gas and diesel Chevy GMT900 trucks along with the diesel Jeep Grand Cherokee seen in our Aug. '07 issue.
One look at the numbers below and you'd think the diesel would win at every stoplight, but in the real world, you don't get to use 4WD and tickle the pedals until full boost is achieved. Of course, the gas truck suffers from annoying throttle interference caused by the computer, which can make it feel sluggish anytime it's spinning below 4,500 rpm and the pedal isn't quickly mashed to the floor. When you try to put your foot through the carpet, the 6.0L Vortec gasser feels like a normal, old-fashioned EFI Chevy with no lag before the acceleration begins.
LACR served the greater Los Angeles area for more than 40 years and there is hope that the Antelope Valley Raceway Committee will be able to persuade local municipalities and Los Angeles County to approve a site for a new dragstrip. For the latest information, check out the Web sites www.lacr.net and www.savelacr.com.
MPG TestIt's not easy to get reliable fuel economy figures while driving the streets and freeways of Los Angeles. Unfortunately, depending on the part of town, the time of day, and the number of high-speed police chases, you can spend more time sitting still with the engine idling than traveling miles for each gallon of fuel burned (a condition also known as zero mpg).
Another way of looking at the data we collected here in the City of Angels is that these may be the most real-world numbers you'll read. We commuted to work through the slop, drove to the dyno shop and made full-throttle runs, towed a trailer loaded with a monster Suburban 4x4, and hit the dragstrip for multiple high-speed passes. We were not babying the trucks and assume you won't be keeping a brick under your GM's pedal.
Are these the best mpg numbers you can expect? Heck no. We got 19.12 mpg from the same Duramax LMM truck during our first test (Aug '07) by using cruise control on the highway and averaged 13.68 mpg in almost 825 miles of driving. This time, we averaged 11.83 mpg with a best tank of 14.23 mpg, even while driving steep mountain roads and with plenty of time spent sitting along with the other sheep stuck on the 405 freeway.