New Loaded Duramax 6.6L GM Silverado Sierra Cylinder Head LLY

Enhance the performance and reliability of your GM Duramax 6.6L engine with our brand-new loaded 6.6 Duramax LLY cylinder heads, designed specifically for the Silverado and Sierra models. These heavy-duty aftermarket cylinder heads are engineered to meet or exceed OEM specifications, ensuring superior durability and performance, even under the most demanding conditions. Loaded with valves, springs, and retainers, these cylinder heads are ready for seamless installation and built to deliver long-lasting reliability.

Key Features:

• Durable Aftermarket Casting: Our LLY cylinder heads are manufactured with a robust aftermarket casting, providing greater strength and resistance to cracking compared to the factory heads. The thicker casting design is built to withstand high pressure and temperatures, making it ideal for heavy-duty use.
• Loaded with High-Quality Components: These cylinder heads come fully assembled with high-performance valves, springs, and retainers. This setup optimizes airflow and combustion, enhancing overall engine efficiency and power output.
• Precision Engineering: Designed to meet exact specifications, our LLY cylinder heads ensure a perfect fit and reliable performance in GM Duramax 6.6L engines. The precision-machined valve seats and guides offer enhanced durability and optimal sealing, preventing leaks and extending the lifespan of your engine components.
• Application Fit: Specifically designed for GM Silverado and Sierra trucks with the 6.6L Duramax LLY engine, providing a perfect fit and easy installation.
• Core Return Required

Benefits:

• Superior Performance: The thick casting and premium components improve engine performance by promoting better sealing, heat dissipation, and airflow. This results in increased power, fuel efficiency, and reduced emissions.
• Long-Lasting Durability: With reinforced casting and high-strength materials, these cylinder heads are built to last, reducing the need for frequent replacements and repairs.
• Ready for Installation: Our cylinder heads come loaded and assembled, making the installation process quick and efficient. Designed for an exact fit, no modifications are required, allowing you to get your vehicle back on the road with minimal downtime.

Heavy Duty Parts Company – Core Returns Policy

Effective December 17, 2025

At Heavy Duty Parts Company, core returns are essential to our ability to provide high-quality, cost-effective cylinder heads. Returned cores supply critical components—such as keepers, springs, and retainers—that are vital to proper engine performance and allow us to maintain OEM-level quality.

No Upfront Core Charge

Unlike many suppliers, we do not charge a core fee upfront. Instead, we rely on customers to return their used cores within the required timeframe.

Core Return Requirements

• Cores are due within 30 days of the purchase date

• If a core is not returned within 60 days, the product warranty is void

• Unreturned cores will be charged as follows:

  • Cylinder heads under $600: $200 per unreturned core

  • Cylinder heads $600 and above: $400 per unreturned core

Customers needing additional time may contact us to request an extension. Approved extensions will prevent core charges from being applied.

Core Return Process

Cylinder heads are shipped with prepaid core return labels included in packets attached to the outside of each box. If labels are missing, customers should contact us for replacements prior to returning the core.

Core Eligibility

Some cylinder heads do not require a core return. In certain cases, core requirements may be waived at our discretion.

Why Core Returns Matter

• Reused core components help maintain OEM-quality standards

• Core returns allow us to keep pricing competitive

• Recycling cores supports sustainability by reducing waste and conserving resources

This policy applies to all purchases made on or after December 17, 2025.

Send Back All Components

To ensure the quality and integrity of our remanufacturing process, we ask that you return all components that were originally included with your new cylinder head. This includes items such as:

• Rocker arms
• Camshafts (if applicable)
• Any other hardware that came with your purchase

Easy & Free Core Return Process

• Each purchase includes a prepaid core return label in a plastic sleeve on the box.
• Simply pack your core with all included components, attach the label, and drop it off with the carrier—no extra cost to you.
• Returned cores undergo inspection and recycling, ensuring maximum efficiency.

Customer Partnership & Sustainability

By returning your core and its components, you help maintain a reliable supply chain, ensuring we can continue offering top-quality products at the best prices. This process not only benefits your wallet but also contributes to a greener and more efficient automotive industry.

We appreciate your support in keeping our business and the industry running smoothly!

Why Choose Our Duramax 6.6L Cylinder Heads?

Choosing our heavy-duty aftermarket LLY cylinder heads means investing in quality, durability, and performance. Engineered to address common issues with factory heads, such as cracking under pressure, these heads are the perfect upgrade for your Silverado or Sierra. Backed by our commitment to providing premium products, these cylinder heads will keep your engine running smoothly for years to come.

Shipping Information

We ship exclusively to the lower 48 states. Insurance, packaging, and handling are included in the shipping cost to ensure safe and secure delivery.

Warranty Information

Our cylinder heads are backed by a 2-year unlimited mileage parts warranty. The warranty covers parts only and does not include labor or incidental costs. To maintain warranty coverage, the heat tab must remain intact and unaltered.

Contact Us

For more information or assistance, visit our website and explore our extensive selection of high-quality cylinder heads and engine components at Heavy Duty Parts Company.

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Duramax 6.6 LLY