How much horsepower does a 2500HD 6.6 gas have?

The 2500HD with the 6.6-liter gasoline V8 is rated at 401 horsepower. This figure applies to the modern L8T gas engine used in current heavy-duty GM pickups.

The 6.6L V8 gasoline option, introduced for GM’s heavy-duty trucks around model year 2020, is designed to deliver solid on-road speed and capable towing without stepping up to a diesel. For buyers comparing power, the key takeaway is that the gas engine provides strong peak horsepower, while the diesel option emphasizes torque for heavy hauling.

Understanding the 6.6L gas engine in the 2500HD

In the 2500HD, GM’s 6.6-liter gasoline V8, code-named L8T, delivers a strong horsepower figure along with substantial mid-range torque. The official horsepower rating for this engine is 401 hp, with torque rated around 464 lb-ft, making it competitive in the heavy-duty gas segment and a viable alternative to diesels for many buyers.

Horsepower figures by model year

The following figures reflect the contemporary 6.6L gas configuration used in Silverado/Sierra 2500HD models since its introduction:

• 2020–present: 401 horsepower at 5,600 rpm (roughly 464 lb-ft of torque at about 4,000 rpm).

Across model years, the 6.6L gas option has maintained the same horsepower rating, with torque numbers remaining in the same general range. Real-world output can vary slightly with gearing, axle options, and drivetrain configuration.

Gas vs. diesel: a quick horsepower and torque comparison

To put horsepower in perspective for buyers weighing gas versus diesel, here is a concise comparison of the two configurations typically offered on the 2500HD:

• Gasoline 6.6L V8 (L8T): 401 hp and about 464 lb-ft of torque.


• Diesel 6.6L Duramax: around 445 hp and about 910 lb-ft of torque.

While the gas engine delivers strong peak horsepower, the diesel option provides substantially higher torque, which translates to higher towing and hauling capability in many situations. Transmission, axle ratio, and gearing also influence real-world performance for both configurations.

Additional considerations for buyers

Horsepower is only one part of the equation. For heavy-duty trucks, torque, payload capacity, towing capacity, and drivetrain setup are equally important. Prospective buyers should consider how the truck will be used—daily driving vs. heavy towing—and whether fuel economy, maintenance costs, and fuel type (gas vs. diesel) align with their needs.

Summary

The 2500HD’s 6.6-liter gasoline engine offers a robust 401 horsepower, making it a strong choice for buyers who want solid performance from a gas-powered heavy-duty truck. When stacked against the diesel Duramax option, the gas engine trades some torque for higher peak horsepower, while the diesel typically leads in max towing and low-end pulling power. Understanding how you’ll use the truck will help determine which configuration best fits your needs.

Is a gas 2500 better than diesel?

A gas 2500 is not inherently "better" than a diesel; the right choice depends on your needs. Gas is generally more affordable upfront, has lower maintenance costs, and is quieter, making it suitable for general use and lighter towing. Diesel is better for heavy-duty tasks like frequent, heavy towing and hauling, as it offers superior torque and better fuel efficiency under load, even though it has a higher initial purchase price.
 
Choose gas if:

• You need a truck for general use, like daily driving or occasional light towing. 
• You want a lower initial purchase price and less expensive routine maintenance. 
• You prioritize a quieter ride. 

Choose diesel if:

• You frequently tow heavy loads, such as large trailers or construction equipment. 
• Your work requires the long-term durability and high torque of a diesel engine. 
• You drive a lot of miles and can benefit from the diesel's better fuel economy under load, which can lead to long-term savings. 
• You want better resale value in a heavy-duty truck market, especially for work-related use. 

Are 6.6 gas engines reliable?

Yes, the GM 6.6L gas engine is considered reliable, especially due to its robust, overbuilt design that lacks cylinder deactivation, but it can have issues with direct injection carbon buildup on the intake valves and potential oil consumption. It is known for its durability and is expected to last for high mileage if properly maintained. 
Strengths:

• Durability: Features a cast iron block, forged internals, and no cylinder deactivation (Active Fuel Management/Dynamic Fuel Management), which contributes to its long-term reliability. 
• Simple design: It is simpler and has fewer complex emissions systems than a modern diesel engine, which often leads to better reliability. 
• Long-term potential: Designed to be a workhorse engine capable of reaching high mileage, potentially 300,000 miles or more with proper maintenance. 
• Fuel flexibility: Can run on standard 87 octane fuel. 

Potential drawbacks:

• Direct injection carbon buildup: The direct injection system can lead to carbon deposits on the intake valves, which may cause power loss or rough idling over time and require cleaning. 
• Oil consumption: Some owners report that the engine can consume oil, a common issue in large engines, especially when towing, so monitoring and topping off the oil is important. 
• Transmission pairing: Some owners express concerns about the reliability of the 10-speed transmission paired with the engine, citing a separate issue from the engine itself. 

Conclusion:
The 6.6L gas engine is a reliable choice for a heavy-duty truck, especially for those who prioritize long-term durability and simplicity over maximum towing performance. To ensure long life, regular oil changes and awareness of the direct injection carbon buildup are important maintenance considerations.

What is the life expectancy of a 6.6 L V-8 gas engine?

Overall, the average life expectancy of a 6.6 Duramax engine falls around 200,000 miles or 320,000 km, depending on driving behaviours, usage, and how often the engine is maintained.

What is the gas mileage on a Chevy 2500 6.6 gas engine?

A Chevy 2500 with the 6.6L gas engine gets approximately 13 to 16 mpg in mixed driving, but this can vary significantly based on driving conditions and the specific trim level. Some users report lower mileage, especially with heavier loads or after the engine is broken in, while others see slightly better results, especially on the highway.
 
Factors influencing MPG

• Driving conditions: City versus highway driving, speed, and "start and stop" use all affect mileage. 
• Vehicle load: Towing or carrying heavy loads will significantly decrease fuel efficiency. 
• Trim level: Certain trims may have slightly different EPA estimates, though real-world mileage varies. 
• Engine break-in: Early mileage may be lower until the engine is fully broken in. 

Average expected mileage

• Mixed driving: Around 13 to 16 mpg. 
• Highway driving: Closer to 16 to 21 mpg for some trims, but often lower due to the truck's size and weight. 
• Towing: Lower, often in the single digits, depending on the trailer weight and conditions.