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  • 2015 Chevrolet Silverado 2500HD Duramax and 2500HD Vortec - Gas vs. Diesel

2015 Chevrolet Silverado 2500HD Duramax and 2500HD Vortec - Gas vs. Diesel

The Tale of the Two Heavyweights: Exploring gas versus diesel in a heavy-duty

Lee Lovell
Oct 20, 2014
Photographers: Jason Gonderman, Robert Guio
The debate of whether to buy a gasoline or diesel-fueled engine has been going on longer than many readers of this magazine have been alive. And much like politics, people leave these arguments even more convinced that their preferred powertrain is the best and the other is an abomination in the automotive world.
As you can likely tell, this is going to be another one of those stories. It would also be fair to ask what the point of doing another one would be, especially after we just stated you pretty much can't change people's minds on the subject. Well, the truth is, with how refined today's modern gasoline and diesel engines have become, choosing one over the other isn't as easy as it used to be. Mostly, it comes down to what you value most and good old-fashioned money.
To figure out which is better in the world of heavy-duty pickups, we got behind the wheel of two 2015 Chevrolet Silverado 2500HDsone with the gasoline-fed Vortec 6.0L V-8 and the other with the diesel-digesting Duramax 6.6L V-8—and got to work.
Photo 2/12   |   2015 Chevrolet Silverado 2500HD Duramax Rear Three Quarters
Power
Ask diesel enthusiast what they love most about oil-burners, and the answer will likely be power. In the case of these 3/4-ton heavy-duty pickups, we can't blame them here. The 6.6L diesel produces 397 hp compared the 6.0L V-8's 360 hp. However, those numbers only tell half of the story: The Duramax churns out 765 lb-ft of torque, more than double that of the Vortec's 380 lb-ft. When you consider that both trucks weigh in excess of 7,100 pounds, the oil-burner has the clear advantage.
That's not to say the Vortec engine is a slouch. With 90 percent of the available torque delivered as low as 2,000 rpm, the gas V-8 will adequately take care of any driving scenario you give it. That's the problem, though; it's just adequate, and to be brutally honest, it feels like hybrid could likely accelerate faster than this beast. Driving around the streets of Los Angeles, where the ability to merge quickly is a necessity, a mash of the skinny pedal is met with more noise than go, although we'll never complain about having to listen to that naturally aspirated V-8 burble. Admittedly, the big city is not the natural habitat for a 3/4-ton, so this isn't as much of a concern in less-populated areas. Its gas-fed competitors from Ram and Ford are powered by 410 and 385hp V-8s, respectively, so it's fairly easy to imagine what this powertrain could do with more power.
The Duramax, though, seems much better suited for the task of hauling the truck's mass around. Although lag from the turbo is apparent, it spools up relatively quick and the engine's 765 lb-ft is put to work quite nicely. That massive amount of twist, plus the fact that all of it is available at a low 1,600 rpm, is a clear testament to why many prefer diesels. Daily driveability is also improved with a 0-60 mph time of 7.2 seconds. However, it is important to note the GM's crosstown rivals, Ram and Ford, rate their diesels at 865 and 860 lb-ft, respectively. Rumor has it that GM has a significant update in the works for the Duramax to debut soon, so stay tuned, as it is doubtful GM will remain content with being third best.
Photo 6/12   |   2014 Chevrolet Silverado 2500HD Vortec Side View
Capability
Another merit diesel enthusiasts love to boast about is towing capacity. Interestingly, there is no clear winner here, at least as far as the numbers are concerned. Using the SEA J2807 towing standard, Chevrolet rates the ball-hitch towing capacity of both the Duramax and the Vortec models we tested at an even 13,000 pounds. However, when trailering with a fifth-wheel, the Duramax takes a 3,100-pound advantage over the Vortec at 17,100 versus 14,000 pounds.
As far as payload capacity is concerned among our testers, the Duramax wins with a rating of 2,793 pounds. That said, our Vortec tester came with the gaseous option ($9,500) that, when equipped, drops the payload rating to 2,493 pounds—most likely due to the CNG tank that consumes nearly a third of the 6 1/2-foot bed. Order a 2500HD without it, and payload actually jumps to 3,152, besting the Duramax by 359 pounds.
Regardless of whether you're hauling stuff in the bed, on the fifth-wheel, or on the ball hitch, the Duramax certainly has the advantage here, where torque is king. Where gas engines typically take an efficiency hit under a heavy load, the diesel's 765 lb-ft of torque will keep pulling strong under acceleration and when attacking a grade. Because of that efficiency, fuel economy for the Duramax doesn't take as big of a hit when compared to a gas engine. Both came with an integrated trailer-brake controller, but the Duramax also takes the advantage here with a standard exhaust brake. The system closes off the exhaust by use of the variable-geometry, causing backpressure in the exhaust manifold and dynamically slowing down the engine without using the brakes—a serious advantage when trailering a heavy load down a hill.
Photo 10/12   |   2014 Chevrolet Silverado 2500HD Vortec Dash View
Economy
When looking at how economical an engine is, it's purely a number game and one that almost always goes in favor of diesels. Because these are 3/4-ton trucks, you won't find any EPA fuel-economy estimates on the window sticker, and likely for good reason. You can imagine our reactions when our testing on the Vortec yielded 10.3 mpg in a healthy mix of city and highway driving—we anticipated it to be bad, but not that bad. As expected, though, the Duramax is the clear winner here, having achieved 15.3 mpg. Yep, that is about 50 percent better fuel economy than the Vortec. Fuel consumption differences will become even more apparent when hauling a heavy load.
But here is where diesel hits its biggest objection: price. Tick the box for the oil-burner and you will have to hand over $8,395. That can buy a lot of gasoline, even to make up for the loss of fuel economy. But while that may be the biggest argument against diesels, we doubt that has changed many people's minds. After all, it is hard to go back after you've experienced the addicting torque of a diesel.
So, which one is better? Well, it depends. After all, each engine will work great at any challenge thrown its way, and with how refined both engines have now become, you'd likely never be able to distinguish between them from behind the wheel. That is, until you step on the accelerator and discover how different these two beasts they are. At this point, you just need to determine your priorities and how deep your wallet is.
Photo 11/12   |   2014 Chevrolet Silverado 2500HD Vortec Engine View

Break Even Point: 104,938 miles
Based on AAA's current national fuel price averages of $3.43 per gallon of gasoline and $3.80 per gallon of diesel. Silverado 2500HD Vortec V-8 average fuel economy of 10.3 mpg combined, Silverado 2500HD Duramax V-8 average fuel economy of 15.3mpg combined.

2015 Chevrolet Silverado 2500HD Duramax

BASE PRICE $49,325
PRICE AS TESTED $62,925
VEHICLE LAYOUT Front-engine, 4WD, 5-pass, 4-door truck
ENGINE 6.6L/397hp/765–lb-ft turbodiesel Duramax V-8
TRANSMISSION Allison 1000 6-speed automatic
CURB WEIGHT 7680 lbs
0-60 MPH 7.2 sec
QUARTER MILE 15.6 sec @ 86.8 mph
BRAKING, 60-0 MPH 134 ft
TESTED FUEL ECON 15.3 mpg

2015 Chevrolet Silverado 2500HD Vortec

BASE PRICE $42,655
PRICE AS TESTED $58,800
VEHICLE LAYOUT Front-engine, 4WD, 5-pass, 4-door truck
ENGINE 6.0L/360hp/380–lb-ft Vortec V-8
TRANSMISSION Hydra-Matic 6L90 6-speed automatic
CURB WEIGHT 7,184 lbs
0-60 MPH 8.5 sec (est)
QUARTER MILE 16.6 sec @ 83 mph (est)
BRAKING, 60-0 MPH 128 ft (est)
TESTED FUEL ECON 10.3 mpg
Photo 12/12   |   2015 Chevrolet Silverado 2500HD Duramax Front

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