More Power Under the Hood

December 13, 2016 03:02 PM

By Kent Sundling

GM kicks torque and horsepower up a notch with new Duramax engine 

For several years, GM has been working behind the scenes on a new diesel for heavy-duty trucks. In October, the fifth-generation Duramax made its debut at the Texas Motor Speedway. Mr. Truck was on hand to put the new engine through the paces.

When it comes to towing capacity for diesel trucks, GM has lagged behind Ram and Ford in recent years. When towing a 10,000-lb. trailer with the Duramax L5P, you can feel the new power—455 hp—and smoke the tires—910 lb.-ft. of torque. At those numbers, GM jumps to second place for torque ahead of Ram Cummins (900 lb.-ft.) and Ford Power Stroke for horsepower (445 hp). 

The 2017 Duramax has undergone the biggest changes since 2001—new turbocharger, pistons, rods, crankcase, fuel pump and emission systems. The Allison auto transmission was tweaked to work alongside the new power.

On the outside, the new hood with Passive Induction System stands out. As an aftermarket add-on, cold air intakes with better air flow filters have resulted in a slight increase in torque and horsepower. But GM’s new air intake doesn’t increase power—it saves power by cooling the engine when under load. Some of the intake air still comes in through the grill. The hood scoop sucks in the air in a U-turn fashion then it hits a wall where the heavier water in the air collides and exits out of a nipple similar to air filters on tractors. The lighter air completes the U-turn then drops down into the air filter on the passenger side fender. According to GM engineers, this new air intake hood scoop doesn’t suck water into the engine air filter in extreme weather.

The Duramax L5P diesel is 38% quieter compared with 2016 models thanks to shielding in the valve covers and less air coming through the grill. New glow plugs and injectors start the engine faster. 

The DEF fill cap is still under the hood, though it is 7 gal. instead of 5 gal. GM lets the power spin in first gear under load (Ram and Ford diesels torque limit first gear and in some configurations second gear to keep the wheels from spinning with a load). 

The new Duramax allows for B20 diesel, and for the first time you won’t have to prime the pump to start the engine if you run out of fuel or are changing fuel filters. 

To my surprise, GM is happy to remain at the current tow rating of 23,000 lb. for a gooseneck trailer, which keeps them in third behind Ram 3500 at 31,250 lb. and Ford F350 at 32,000 lb. Why get back in the game with more power and not match tow rating? GM says few of their customers tow trailers heavier than 20,000 lb.

Pickups are in the closest race I’ve seen in 50 years. I’m guessing Ram will have the next power increase as their truck sales now beat GM in half-ton and heavy-duty categories. 

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Spell Check

A Minnesota City.3, MN
1/6/2017 07:03 PM

  So why bother to raise the power?, when your not going to be able to pull a heavier load?, selling to the guys who do? I have a 30ft cattle trailer, with '11 Ford 350 dually, diesel pulling it. Haul 14 fat steers, that av. well over 1500# when weigh after a over night stand at sales barn. It has plenty of power at less than 850 pounds & hp of 385 i think it was. I know i'm way over GVW weight for the truck, that's amounts to 36550, it was around 32 when i bought it or less & trailer tow, down in the low 20's. But can easily break the speed limit, with all that power, like to do 75 to 80, loaded. More power equallys more fuel use, & that's not good. I get sleepy at 60, more exciting at higher up..... So new chevy should be able to handle it too, right????


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