6.6 Duramax Vs. 6.6 Gas: Which Chevrolet Silverado Engine Is Best?

The Chevrolet Silverado HD — and its corporate twin in the GMC Sierra HD — can be had with either a standard 6.6-liter gasoline V8, or the optional 6.6-liter Duramax turbo-diesel. Opting for the TD brings a higher price, increased torque output, and superior towing performance. Is the Duramax worth the extra purchase and running costs? For a lot of buyers, the answer is yes. But don't sleep on the gas engine.

Gasoline versus diesel is a choice that heavy-duty pickup buyers have had to make for a long time. That decision has only gotten harder in recent years, with both GM's new 6.6 and Ford's "Godzilla" 7.3-liter rolling out for heavy-duty pickups. Traditionally, diesel powerplants have proven that their extra torque is usually the more capable and preferred option for heavy duty hauling. The question then becomes whether these improved, more powerful gasoline V8s are capable of doing enough to win over diesel-buyers.

At a glance, the Silverado HD's two engine options may look similar, but those similarities end once you get past their displacement and cylinder layout. The standard engine in all 2025 Silverado HDs is GM's L8T gasoline V8. There are no turbochargers, no overhead cams, just 6.6 liters of old-school, naturally aspirated, pushrod V8 muscle — with a nice sprinkling of modern tech, including direct injection. The L8T makes 401 horsepower and 464 pound-feet of torque, with peak torque arriving at 4,000 rpm.

Those looking for more pulling power can opt for the available 6.6-liter Duramax turbo-diesel V8. It makes 470 horsepower, and more importantly, a massive 975 pound-feet of torque at just 1,600 rpm. Just how much will that big jump in torque cost you? The Duramax upgrade from the base gas engine runs a little over $10,000. No matter which engine you choose, it will come mated to a 10-speed automatic Allison transmission.

The primary benefit of spending that extra money is improved towing capacity. When equipped with the Duramax engine, the Silverado HD can tow up to 36,000 pounds — more than double the 17,400-pound maximum towing capacity of the gasoline engine. Even if you aren't planning on pulling 36,000 pounds worth of stuff, the Duramax will be the less stressed and more fuel-efficient choice for towing, thanks to its low-rpm torque. With that said, the gasoline Silverado HD is no slouch for towing.

Whether it's for work or for hauling around weekend toys, the availability of a big diesel engine is the primary reason many buyers choose a heavy-duty pickup truck. And for those buyers, opting for the Silverado HD's Duramax should be an easy choice.

That doesn't mean the gasoline Silverado HD is a bad choice. Not only is it cheaper to buy, but it's easier and cheaper to fuel, with the gas V8 designed to run on good old 87 octane fuel. You also don't have to worry about the diesel exhaust fluid (DEF) required with modern diesel trucks, and will generally be dealing with a less complex powertrain overall.

Whether you opt for the gasoline V8, or the upgrade to the Duramax, you'll get to appreciate a lot of the improvements GM has put into these engines in recent years. It's really just a matter of how much torque you need, and how often you need it for heavy-duty towing.