GM Gen III V-8 Cylinder Head Comparison - Gen III Tech

Important: In January, 2004, the depth of the blind, threaded head bolt holes on the Gen III V-8 engine blocks were changed to use the common head bolt, PN 17800568. There was not a new engine block part number issued for this change, so it is difficult to determine what head bolts you will need until you see the existing head bolts in your engine.

"Lost" Power For the sake of mass production, the production Gen III V-8 cylinder heads were designed to fit the smallest-bore Gen III V-8 engines-the 4.8L and 5.3L, 3.780-inch-diameter cylinder bore SUV and truck engines. The displacement difference between the 4.8L and 5.3L engines is created with the stroke. The 4.8L engine uses a 3.27-inch stroke crank, while the 5.3L engine has the common Gen III V-8 3.622-inch stroke crank. Since the 5.7L and 6.0L Gen III V-8 engines have 3.898- and 4.00-inch bores, respectively, this means there is room for larger valves and better valve placement in the larger bores.

Why did GM do this? For every LS1 or LQ9 engine built, there are about two 4.8Ls or 5.3Ls built. The 5.3L is GM's bread and butter, so the heads had to be common to work with all the designs.

Virtually every GM engineer who worked on the Gen III V-8 knows there is power in moving the valve spacing to install bigger intake valves and achieve improved flow into the engine. They also know this change would require a new intake port design, offset rockers, and other changes to accommodate the design, but the power potential is great enough to warrant this work.

Obviously, a cylinder head with all these changes requires considerable work to create and manufacture, but it's possible it might appear in the near future-the multiple-digit power potential is too great for hot rodders to pass up. For those not capable of creating a cylinder head, just know there is power left on the table there!