The Gen IIIs were designed...
The Gen IIIs were designed for manufacturability, so many of the connectors, fittings, and systems are not familiar to hot rodders, which can lead to a frustrating, expensive experience trying to remove an engine. The book "How to Build High Performance Chevy LS1/LS6 V-8s" has one chapter dedicated completely to removing and reinstalling the Gen III engine. It has more than 160 images to show how to remove the Gen III from GM fullsize trucks and SUVs, along with the Corvette, Camaro, and Firebird.
The cylinder heads are the big story on the LS1 Gen III V-8. Not only do they look serious with their symmetrical "cathedral" intake ports, aggressive exhaust ports, small combustion chamber volumes, and slick investment-cast rocker assembly; they make serious power in just about any application with little work.
GM veterans and brothers Ron and Ken Sperry spearheaded the design and development of the heads. With almost 80 years of GM development experience between them, the Sperrys were allowed to lead their teams to develop the best production head design ever. These heads have been used to support normally aspirated 800hp street nasties, 1,000hp centrifugally blown bruisers, and 1,400hp turbo killers. For more details, check out the sidebar on the head specs for more on this great design.
If there is one drawback to the production heads, it's that the engineering team was only allowed to build one head, and it had to fit all the Gen III V-8 engines. This means the valve spacing and chamber shape on the head are for the smallest bore engines: the high-volume 4.8L and 5.3L truck engines. These engines have 3.780-inch/96mm bore diameters. GM did this to minimize tooling expenses and to maximize its initial engineering focus, knowing full well that it was sacrificing real power. This is a good example of the many everyday compromises a large-scale manufacturing company like GM must make to maximize success, but it also highlights an opportunity for the aftermarket and performance enthusiast.
Whether in the engine bay...
Whether in the engine bay or out of a vehicle, the Gen III V-8 is very straightforward to disassemble. For instance, the intake manifold is held on the engine with 10 "nested" bolts. Once unscrewed from the cylinder heads, the intake usually requires slight prying and pops off. No water or oil touches the nylon intake, so this step is completely dry.
The engineering team at GM estimates a set of heads built specifically for the 3.898-inch/99mm, 4-inch/101.6mm, and larger bore spacings would release at least 15 to 25 hp-thinking in terms of the stock engine. A performance engine would obviously see greater gains.
Now, this is no small undertaking. To take full advantage, the intake and exhaust ports would need to be reworked, the rockers and lifters would need to be offset to attain proper valvetrain geometry, and the combustion chamber would need to be considerably altered. Will it happen? More than likely, yes, as the engine has so much groundswell interest and power-producing potential. The question is more when, not if.