2015 Gmc Sierra 2500 Denali on 2040-cars

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2018 GMC Acadia with 'Christmas Aero' modification gets in the wind tunnel

Tis the season of "Big" - big cheer, big parties, big bowls of eggnog, big decorations, and when it comes to your family hauler, big drag. Festive drivers who festoon their crossovers, minivans, and SUVs with wreaths, Rudolph noses, fuzzy antlers, and rooftop Christmas trees undo the years of work that car engineers devote to fractional gains in fuel economy. To put numbers to such fuel-guzzling madness, GMC started with a 2018 Acadia, optioned it with the Xmas Aero Package - both Standard and Plus versions - put it in Lockheed-Martin's wind tunnel. The resulting dip in fuel economy results probably won't surprise anyone who's used a roof rack - or, for that matter, their car's air conditioning. However, it might surprise you to find out which seemingly substantial decoration had no effect, and which seemingly innocuous decoration was about twice as bad as running the A/C on its Mr. Freeze setting. Check out the brief video above for the results. And consider placement of that bow carefully.

11 vehicles from Barrett-Jackson Las Vegas worth watching

This weekend will see the world's collector car crowds descend on Las Vegas, NV for one of the biggest shows on Barrett-Jackson's popular auction circuit. There are hundreds of vehicles up for bidding, ranging from a brand-new Lamborghini Aventador to a spattering of Art Deco classics and a huge swath of classic muscle cars.
While it's virtually impossible to assemble an inarguable list of the best cars coming during the three-day, 700-plus vehicle auction, we've sifted through the listings for this year's show - it was a tough assignment, we promise - and assembled a list of what we think will be some of the most interesting lots. We'll admit, it's a bit heavy on American iron, but if you browse BJ's listings, you'll come to a similar conclusion. Still, scroll down for our list of what we think will be the most interesting vehicles at the upcoming auction.

Leaked GM document shows GMC Sierra I6 diesel is more powerful than F-150's

GM told us earlier this year that the 2019 GMC Sierra would be getting a 3.0-liter I6 diesel option, but it never mentioned power or fuel economy figures. Hold the phone though, because a leaked GM Canada document just showed up online that lists out the details we've been waiting for. Originally published by TFL Truck, the 3.0-liter oil-burner supposedly makes 282 horsepower and 450 pound-feet of torque. For those who are counting, that's more than the Ford F-150's 250 horsepower and 440 pound-feet from its 3.0-liter diesel. It soundly bests the 240 horsepower and 420 pound-feet of torque from Ram's 3.0-liter diesel as well. Fuel economy is another story, though. The promotional material states that it will get 28 mpg on the highway, which is 2 mpg short of the F-150's 30 mpg — mind you, it's only capable of that magical 30 mpg figure in rear-wheel drive form. There's another caveat here, too; these are numbers for Canada, so they're not exactly finalized EPA figures. However, we wouldn't expect drastic differences between the two when the American numbers come out. The leaked documents also state the diesel Sierra will be capable of towing 7,800 pounds. That number seems remarkably low when compared to the F-150, which can tow up to 11,400 pounds with its diesel. Extra power and torque would have us assume that GM could get even better numbers than Ford, so we're going to hold our final judgment for official word. A 10-speed automatic will do the shifting on the diesel, just like on the 6.2-liter V8. Since the Chevy Silverado is also expected to get this engine, we can assume the figures would be almost, if not identical, to those we see here. We recently drove the 2019 Sierra and Silverado without the diesel engines, so go check those reviews out if you'd like to know more of our thoughts on the redesigned GM trucks. Related video: