Are you rebuilding or just looking to increase your Duramax's strength? If you are planning on upgrading the power your engine puts out it's a good idea to increase durability and eliminate cracking. Industrial Injection's New Heads for the Duramax LLY are a great place to start because these brand-new GM OE cylinder heads have a reinforced casting to make them more durable and help eliminate cracking. Each head has been pressure tested and comes fully loaded. SOLD AS A PAIR.