LS3 Engine Engineers - Inside Information

In a VETTE exclusive, we introduce you to some of the engineers in charge of the Corvette's LS3 engine components. Part 2: Cylinder heads, head bolts, camshaft, and intake manifold

Christopher R. Phillip Jun 1, 2011 0 Comment(s)
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Head Bolts
Name: Eric Nordling
Title: Design Responsible Engineer
Years with GM: 11

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Other experience: Six years of finite-element analysis prior to GM, eight years as Lead Analysis Engineer for overhead-cam engines, and three years as the Small Block Assembly Sealing and Fastening Design Responsible Engineer

What LS3 parts are you responsible for? Engine fasteners, seals, and joints

What LS7 and LS9 parts are you responsible for? Same

What other Corvette parts have you been involved with in the past? None

Why do you think your LS3 part is the most important part on the engine? What holds your LS3 together can't fail, period. Fasteners that come loose allowing the joint to fail can be catastrophic to the engine, so we use proven design practices and rigorous test schedules to ensure the joint maintains clamp load at all times.

The LS3 head bolts were designed to seal the head gasket under very aggressive driving conditions. The head bolts provide the clamp load required to seal coolant, oil, and combustion gas from leaking out of the engine at the head-to-block interface. To ensure the head gaskets will always survive, we study the engine loads under all ranges of operation and design the head and block structures to the worst-case thermal and pressure loads. We use dyno testing and analytical techniques to predict and apply these conditions to the engine. We also avoid overloading the joint, because too much load can create high stresses in the head and block, and increase bore distortion. In the case of the LS3, the head bolts have been designed and rigorously tested to provide optimum sealing performance while minimizing the stress on the aluminum structure. [This increases] the overall durability of the engine.

All GM head bolts are torque-to-yield. This means the bolts are stretched a little past the yield strength, so when thermal loads relax the joint, the retained load is sufficient. Torque-to-yield fasteners should never be reused, because they are slightly stretched during the assembly process and can't produce the same load or bolt safety factors the second time they are torqued.

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What is a focus area you watch when designing the LS3 part, especially knowing it is for a Corvette engine? The strength of the block in the water jackets adjacent to where the head bolts attach is a critical area for development. Block engineers are consulted to ensure the stress resulting from the bolt loads in this area is correctly managed. Also closely managed is the placement of threads and counter-bore depth to minimize bore distortion while maximizing bulkhead strength. Proper thread engagement on the head bolts minimizes load loss in the joint due to thread relaxation. What are the current trends with your LS3 part? Where is it going? As horsepower and torque increase in the future, new head bolts may be required, but for now there is plenty of room to up-level power in the current LS3 design.

Compare your part to aftermarket parts of the same item. What makes yours better? When working on engines, it's important to know how the structure affects your clamp load. We use small-block heads, gaskets, and blocks to develop the torque-angle strategy—a more precise way of controlling bolt clamp force—in our fastening lab here in Pontiac, Michigan. The torque-angle strategy is unique for each critical fastener, and it really depends on the structure as much as the bolt. Our head bolts are the best, not only because we control the fastener's yield point very closely, but also because the torque-angle strategy we specify ensures that we achieve the right clamp load in the joint without over-stretching the bolt or over-stressing the aluminum structure.

Do you own a Corvette, a classic car, or have a related hobby? I enjoy building and riding custom motorcycles with my father. I like to help my father-in-law work on his vintage-car collection. I helped him work on his '67 Corvette 427 convertible and, more recently, a '59 Impala. I appreciate the historic significance of working on small-block engines and being able to build upon and improve their great reputation by doing all I can to increase their durability.


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